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GEO 2010
- Conference date: 07 Mar 2010 - 10 Mar 2010
- Location: Manama, Bahrain
- Published: 07 March 2010
1 - 100 of 457 results
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Feasibility of Detecting Near-Surface Cavities Using Integrated Seismic and GPR Techniques
More LessThe feasibility of directly detecting near-surfaces cavities is challenging due to the complexity of nearsurface
materials and the limited resolution of seismic techniques.
Therefore, Shallow seismic survey has been applied for an area of limestone rocks includes subsurface
cavity at depth about 3 meters under the ground surface. seismic waves have been generated and
acquired with high resolution and good quality characteristics along profiles passing through the cavity
with 1 meter geophone spacing and multi-channels seismograph. During a comprehensive sequence of
data processing and using more sophisticated software for refraction tomography and multi-channel
analysis of surface waves (MASW ) , the cavity has detected at about 3 meters depth and about 30
meters of lateral extension has been clearly identified. Furthermore, the location of the cavity has been
confirmed successfully through the application of GPR surveying profiles along the inspected cave
position. The acquired GPR profiles are processed and filtered to minimize the noise effects. High
amplitude reflections are observed within the profile. These high amplitude reflections are good
indicator to the presence of cavity at a depth of 3 meters from the earth's surface with thickness of
about 8 meters and extend laterally for about 30 meters in the profile direction. It noticed that both of
lateral extension and depth to the top of the cavity have been identified through seismic and GPR data
interpretation. It is concluded that, the integration between two different near surface geophysical
techniques is powerful and helpful way in detecting not only the depth for the subsurface features but
also in determining their lateral dimensions.
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Interpreted Strike-Slip Fault Elements in the 1st Eocene Reservoir of Wafra Field, PNZ Kuwait
Authors Nader M. Eloutefi, John Smith and Fahd Al-khaldiThe Wafra field lies in the northwest part of Kuwait/ Saudi Arabia partitioned Neutral Zone (PNZ) and
the 1st Eocene is the shallowest reservoir in the field. The structure of Wafra consists of two parallel
anticlines, trending northwest - southeast. It is proposed that these anticlines are cut by northeast -
southwest elements (strike slip faults). Accordingly, structural compartmentalization has been created
due to horizontal and vertical displacements, with some rotation in the horizontal plane especially in
the southern area of the field. These elements are believed to play an important roll in the
development of structures in PNZ.
This structural domain represents the direct response to two major elements: the extension of Red Sea
to the west, and the compression of Zagros crush zone to the east.
Regionally, many observations have been detected suggesting the occurrence of these elements. These
observations are: Landsat images of Kuwait and Saudi Arabia, sinuosity of the Kuwait coast line, and
structural offset of oil fields in PNZ area i.e. Wafra, South Fawaris & Humma.
So far, micro-scanner image data has proved to be one of the best methods to provide evidence for
the presence of these elements. Abrupt changes in bedding dip attitude, deviation azimuth, and facies
plus the occurrence of intensive fractures are the main evidence for these elements (strike-slip faults).
Structure and pressure maps have been integrated with image data to verify the regional distribution
of these strike slip faults in Wafra area. Current seismic data has insufficient quality to provide support
for these interpretations.
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A Simple Technique for Estimation of Reservoir Permeability from Seismic Reflection Data Based from Biot’s Theorem
Relationships among elastic parameters and rock properties, and ultimate reservoir parameters have
been established in continuum mechanics and rock physics. Therefore, it should be possible to estimate
reservoir permeability from the seismic data. We used Biot's solution of wave equation in an elastic
porous medium and the approximations of Turgut-Yamamoto to allow an establishment of a linear
relationship between attenuation coefficient or amplitude ratio as a function of the inverse of the
square of frequency. The slope of this function includes the permeability. It can be shown that this
technique agrees to the measurement of the permeability of a porous medium from seismic
waveforms. We examined this technique to estimate the reservoir permeability by using synthetic
seismogram data. The result show that has an error less than 5 %, it means that the study of
permeability estimation from surface seismic data is possible by using an accurate calibration step. The
procedure is tested on 3D seismic data over part of Duri field in central Sumatra, Indonesia. The
simplicity of the theoretical approach requires the introduction of an empirical calibration factor that is
provided by well SM#A in the area. This factor is then implemented to estimate the permeability with
seismic data on the field; it gives a permeability map of the study area. A key result of the study is
that permeability estimation with surface seismic data are possible but requires calibration. A
confirmation and validation of this procedure will be subject to future work.
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Neural Permeability Prediction of Heterogeneous Gas Sand Reservoirs
Authors Gharib M. Hamada and Moustafa ElshafeiAnalysis of heterogeneous gas sand reservoirs is one of the most difficult problems. These reservoirs
usually produced from multiple layers with different permeability and complex formation, which is often
enhanced by natural fracturing. Therefore, using new well logging techniques like NMR or a
combination of NMR and conventional open hole logs, as well as developing new interpretation
methodologies are essential for improved reservoir characterization. Nuclear magnetic resonance
(NMR) logs differ from conventional neutron, density, sonic and resistivity logs because the NMR
measurements provide mainly lithology independent detailed porosity and offer a good evaluation of
the hydrocarbon potential. NMR logs can also be used to determine formation permeability and
capillary pressure.
This paper concentrates on permeability estimation from NMR logging parameters. Three models used
to derive permeability from NMR are Kenyon model, Coates-Timer model and Bulk Gas Magnetic
Resonance model. These models have their advantages and limitations depending on the nature of
reservoir properties. This paper discusses permeability derived from Bulk Gas Magnetic Resonance
Model and introduces neural network model to derive formation permeability using data from NMR and
other open hole log data. The permeability results of neural network model and other models were
validated by core permeability for the studied wells.
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Quantitative Characterisation of Intertidal to Supratidal Sediments of the Abu Dhabi Coastline
Authors Stephen Lokier, Alice Knaf and Thomas SteuberThe Abu Dhabi coastline provides an ideal setting for the study of sedimentary systems inferred to be
directly analogous to those which deposited many of the regions Mesozoic petroleum reservoirs.
Improved understanding of these complex depositional environments, supported by quantitative
sedimentological data, is essential to the development of accurate depositional models and reliable
simulations for carbonate reservoirs.
The arid southern shore of the Arabian Gulf has an extremely low-angle ramp geometry. The coast is
locally protected from open marine conditions by a number of peninsulas and offshore shoals and
islands. Sedimentary processes in the supratidal zone are dominated by the precipitation of evaporite
minerals in the shallow sub-surface. A broad carbonate-evaporite intertidal setting, characterised by
complex depositional facies geometries, passes off-shore, into a subtidal carbonate depositional environment.
The coastline of the United Arab Emirates is currently undergoing massive infrastructure development
at an unprecedented scale, with huge dredging and island-building projects changing the sedimentary
dynamics of the coast beyond recognition. The impending loss of many of the natural coastal systems
gives further impetus to the need for accurately recording these sedimentary environments before they
are eradicated by the anthropogenic overprint.
This study employs a range of analytical techniques to investigate and characterise the surface.
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Characterization of Ahmadi Reservoir of Bahrain Field with DFN Model Using Transient Well Testing
Authors Ammar A. Shaban, Thierry Le Maux and Laurent GhilardiniThe Ab formation of the Ahmadi group in is one of the most difficult reservoirs to produce in Bahrain
Field. It has tight matrix with low permeability and complex fracture system makes it difficult to
produce. Hence, the understanding of such fractured systems is essential for modeling and improving
the production and ultimate recovery from this reservoir. To help with that, Discrete Fractured Network
(DFN) modeling has been used to characterize this fractured reservoir. If integrated with other data
from the field, DFN can provide more representative fractured models. Transient Pressure Welltesting,
a widely known applied reservoir characterization technique, can be used to validate the suggested DFN models.
This paper presents the work that incorporates a sensitivity analysis study used to test and investigate
the parameters that have a direct effect on the curve signature of the transient pressure welltest
analysis and their interpretations.
Different customized DFN models were built and simulated to obtain the pressure measurements under
different scenarios. Various pressure derivative curves were generated and compared to investigate
the sensitivity of fracture parameters on the signature responses.
The study concludes with actual field cases from the Ab fractured reservoir.
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Depositional Environment and Sequence Stratigraphy of the Neocomian Fahliyan Formation in the North Dezful Embayment, SW Iran
Authors Mostafa Sabouhi, Davood Jahani, Farid Taati Qurayem and Ali AminzadehFahliyan Formation (Neocomian) is one of the important hydrocarbon reservoirs of khami group in
south west of Iran. This Formation has 332m thickness in type section and mainly consist of carbonate
rocks. In this study,the Fahliyan Formation was investigated in subsurface section of AZN#B Well in
the north Dezful Embayment(with281m thickness). Lower boundary of Fahliyan Formation with Garau
Formation is continuous and the upper contact with Gadvan formation is conformable According to this
study 13 carbonate microfacies and one shaily facies were recognized which are grouped into four
facies associations micro facies group). These facies associations present platform to basin depositional
setting and are nominated as : A (Tidal-flat), B (Lagoon), C (Bar) and D (Open marine).
Based on available data set including cutting samples,thin sections and well log analysis, it seems the
Fahliyan Formation was deposited in a Carbonate shelf setting and the studied profile indicates the
shallowest part of the platform.Vertical succession of microfacies and relative depth changes of the
Fahliyan Formation led to identification of two third-order depositional sequence. The first sequence
includes HST only and the TST is in the Garau Formation. The upper boundary of this sequence is a
type 2 (SB2). The second sequence includes TST and HST,and upper boundary with The Gadvan
Formation is type 1 sequence boundary (SB1).
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Magnifying the Numerical Aspects of Convection-Dispersion Equation by Selecting Different Methods and Grid Sizes
More LessVirtually all reservoir simulators obtain solutions to fluid flow equations, usually nonlinear partialdifferential
equations, by, making discrete approximations to derivatives.1 Whether finite-difference or
finite-element methods are used, these approximations always introduce truncation errors that often
can distort the accuracy and stability of the solution. The truncation error is often referred to as
numerical dispersion because, to lowest order, it can be represented as a second spatial derivative
term,2 added to any true dispersion term in the problem.
Distortion of numerical solution is most significant in the simulation of EOR processes3 where sharp
displacement, concentration, and/or temperature fronts are an important part of the efficiency of the
processes, and artificial smearing as a result of numerical dispersion can render the simulation meaningless.
At this paper to investigate the effect of solution method on Numerical Dispersion two computer
programs that the first one is based on method of Finite Difference and the second is based on method
of Line-Explicit are written in MATLAB Software. Also at this paper stability of 9 cases that are included
various time and distance weighting for each method are discussed. In continue the effect of grid sizes
(Δx) on smearing and oscillation is investigated by selecting various values for Δx. The results indicate
that by using the method of Line-Explicit as solution method for general difference equation (equation
(32)), numerical dispersion will be minimized. Also, it is showed that cases of 7, 8, and 9 have
minimum numerical dispersion. At the last part of the paper, as it can be seen from Figures.37-54
decreasing the grid sizes, reduces the numerical dispersion.
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Deposition of Retrogradational Carbonate Grainstone Shoals and Subsequent Basal Barrier (Sole Seal) Development by Deposition and Diagenesis - Lower Cretaceous Ratawi Oolite Reservoir (Minagish Formation) Wafra Field, PNZ-Kuwait
Authors Osama M. El-Gendi, John Weston and Bader Al-OtaibiThe Wafra field is located in the Partitioned Neutral Zone (PNZ) between Kuwait and Saudi Arabia and
has been producing medium oil from the Ratawi Oolite Limestone reservoir since 1956.
The Wafra Ratawi is an example of a detached rimmed shelf carbonate shoal depositional system
deposited on a paleo-high in the Late Cretaceous. The depositional architecture was analyzed for major
depositional controls and to explain the existence of a sole seal (Basal Barrier) that restricted early
water encroachment and contributed greatly to the productivity of the reservoir.
The carbonate platform is made up of allochem Oolitic limestone shoals (grainstones) during relative
sea level stagnation in an overall transgressive retrogradation shoal system with shallowing upward
sequences. The reservoir is structurally trapped on three sides and stratigraphically trapped on one
side where tighter, off-shoal deeper marine carbonate wackestones and mudstones provide the
necessary reservoir seal.
As the leeward and windward carbonate grainstone shoals developed, a tighter carbonate mudstone
was deposited by reduced circulation of nutrients and aeration, and increased excessive heat, resulting
in a low stand system tract (LST) lagoonal facies. The retrogradation of these grainstone shoals with
intervening lagoonal facies resulted in a continuous development of a tighter facies across the field,
enhancing a substantially facies-driven sole-seal to the reservoir called the Basal Barrier. Diagenetic
cementation of the Basal Barrier (possibly due to Neomorphism or re-crystallization of pre-existing
carbonate fines) further reduced the sole seal permeability restricting bottom aquifer support, resulting
in lower water production for much of the production life.
As transgression continued, the grainstone forming carbonate factory was over-whelmed and drowned
by a rapid rise in sea level during the transegressive system tract (TST), and tighter, deeper marine
carbonates capped the main reservoir grainstone shoals. Complete entrapment came with continued
transgression during the highstand system tract (HST) and deposition of tight deeper marine
argillaceous carbonates grading to calcareous shales at the top forming the cap rock to the reservoir.
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Characterisation and Genesis of Oils from Unconventional Reservoirs of Ahmedabad Block, Cambay Basin, India
Authors Neelam Niranjan, Leena John, Anita Sharma and Anil GuptaCambay Basin is endowed with hydrocarbon accumulations in multiple reservoirs of different ages. In
Ahmedabad block reservoirs within Kalol Formation can be identified on conventional logs whereas
reservoir rocks in Cambay Shale are predominantly shaly and unconventional in nature with no
identifiable reservoir manifestations on well logs in fields like Sanand, Jhalora, Wadu and Indrora. The
problem of identification and quantitative evaluation of such unconventional reservoirs is being
addressed by high resolution Resistivity Imaging Tool. Identification of hydrocarbon zones is an
arduous task in such reservoirs but at the same time source of hydrocarbons is also a relevant issue.
The present work is to see if these reservoirs are self sourced or have migrated hydrocarbons.
Oils from unconventional shale reservoirs, developed in Chhatral Member of Younger Cambay shale in
Sanand field in Ahmedabad block have been characterized and correlated with oils from other
reservoirs. Source rock identification and characterization has been carried out from these and nearby
wells using pyrolysis, isotopic and biomarker studies.
It has been found that oils in these unconventional reservoirs are genetically similar to the oils in
conventional reservoirs from the same and nearby wells. The source rock is either absent in these
shales or not mature enough to generate hydrocarbons indicating that hydrocarbons from more mature
Cambay Shale or Olpad have migrated to these locales and is not in-situ generated.
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New Siliceous Microfossils in Permo-Carboniferous Rocks: Extraction, Origin, Application
Authors Holger Cremer, Oscar A. Abbink, Linda Garming, Elisa Guasti and Roel VerreusselLate Carboniferous to Middle Permian rocks resting on the Base Permian Unconformity in the
Netherlands are of great economic significance. The Rotliegend rock sequences contain the most
important gas reservoirs of the Netherlands, the Slochteren sanstones. However, the Rotliegend
reservoir rocks are typically barren of any fossils, including palynomophs, which hampers stratigraphic
control and correlation of these rocks. In a recent attempt of re-evaluation the barrenness of the
Rotliegend, siliceous microfossils, referred to as biogenic silica particles (BSPs), in considerable
morphological diversity could be extracted from these rocks. We applied a three-step approach to
prepare BSP-containing microscopic slides from Rotliegend samples: (1) pre-flotation treatments
aiming at the removal of large particles, organic matter, carbonate and clay, (2) repeated flotation
steps in order to extract and concentrate BSPs, and (3) slide preparation using Naphrax™ as mounting
medium. Many of the newly discovered siliceous microfossils resemble plant stones, so-called
phytoliths, tiny silica bodies of various shape and size that are incorporated as structural elements in
the roots, stems, and leafs of modern plants. Major plant groups like the gymnosperms, lycopods and
ferns existed already by the end of the Devonian which might imply that these early land plants have
also formed phytoliths in their tissues. The here reported BSPs constitute only the second evidence of
phytolith-like siliceous microfossils from the Paleozoic. The newly extracted microfossils may provide a
tool for subdividing and correlating Rotliegend rock successions. In order to test this hypothesis, Permo
-Carboniferous rocks from various wells in the Netherlands were studied. Biogenic silica particles
(BSPs) could be extracted from all studied wells and lithostratigraphic units.
However, the total BSP abundance in the single samples considerably varies. A total of 22 BSPs with
significant morphological differences could be hitherto identified. BSP assemblages in the Rotliegend
are currently examined to determine how they can provide information on stratigraphy. The examined
BSP-based biostratigraphic approaches include first and last occurrence dates and variability in the
down-core abundance patterns. If the stratigraphic importance of BSPs could be confirmed in the
ongoing studies, BSPs will provide a new tool for subdividing and correlating the mostly barren
Rotliegend sequences.
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Application of Soft Computing in Lithology Prediction: A Case Study from Marun Field
Authors Sayyid Reza Asadullahpour and Bahram HabibniaThis paper focuses on prediction of lithology, especially shale intervals. Shale is very significant in
zonation, layering, formation damage and well logs. Neural clustering network (NCN), neural patternrecognition
network (NPRN), feed-forward back-propagation network (FBN), fuzzy clustering means
(FCM) and adaptive neuro-fuzzy inference system (ANFIS) are used. They are tried on three wells in
carbonate reservoirs of Marun field, however results are discussed for Well # 222 with 811 utilized
data of raw log reading.
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Correlation and Integration of Seismic Velocities, Rock Properties, and Pore Structure in from Outcrop of Wasia Group Rocks in the U.a.E
An earlier geological and petrophysical investigation of the Lower Cretaceous, Wasia Group in the UAE
found potential correlations between seismic velocities (Vp and Vs) and fracture density, except for a
group of rock samples that deviates from the general trends. The aim of this study is to better
understand the previous results to improve characterization and correlation of the geology and rock
properties of the exposed rock.
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Integrated Geophysical Investigation of Al Hiyar Area, Eastern Abu Dhabi: Implications for Structure of the Frontal Fold Belts of Oman Mountains
Authors Saif A. Al Mesaabi, Ammar H. El Husseiny, Ahmed A. Hassan and Mohamed AliGravity, magnetic and seismic surveys were conducted in Al Hiyar area, eastern Abu Dhabi, located on
the border between the United Arab Emirates (UAE) and Oman on the western edge of the northern
Oman mountains as part of a study to determine the subsurface structures and sedimentary sequences
of the area. The interpretation of these new data was integrated with a new interpretation of
reprocessed commercial seismic reflection profiles recorded close to the area.
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Structural and Tectonic History of the Sedimentary Basin in Northern Iraq and the Kurdistan Region
More LessThe aim of this study is to address the main aspects of the structural and tectonic evolution of the
sedimentary basin in northern Iraq and identifies all the sedimentary cycles in details from the Late
Triassic period to Pliocene.
The second part tackles the Geohistory modelling of all the encountered source rocks in the basin and
evaluates their maturation history and expulsion of hydrocarbons.
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Challenges Associated with Exploring the Cretaceous Rudist Basin-Margin Buildups of the Arabian Basin
More LessRudist buildups were described from many horizons within the Cretaceous strata of the Arabian Basin.
The most prominent among these were described from the Shuiaba Formation (Aptian) in the major
oilfields of the Arabian Gulf region. They were documented also from the Mauddud Formation (Aptian)
in the eastern offshore areas of Saudi Arabia and southeast Iraq and from the Mishrif Formation
(Albian-Cenomanian) in the southern Arabian Gulf and southern Iraq (e.g. Majnoon field). More varied
buildups were found in the Upper Cretaceous carbonates of the Simsima Formation (Maastrichtian) in
Oman and the UAE, the Hartha Formation (Campanian) in central and west Iraq and from Wadi Sir
Formation (Turonian) in Jordan.
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North Oman Fault Geometries in Outcrops, Analogues and Sub-Surface
Authors Pascal D. Richard and Mohammed Al-KindyNorth Oman offers a rare opportunity for making outcrop observations of faults developed in
formations that are also the producing reservoirs in the sub-surface. It is possible to look in great
detail at fault geometries and associated fault damage zones, both in map view and cross sections.
From these observations it is possible to establish the geometrical rules that will help to build static
models and interpret faults on seismic. It is also possible to illustrate the impact of the simplifications
which are inherent to the static modelling process and assess whether they are acceptable or not to
define the most suitable modelling strategy.
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Spatially Enabled Decision-Making with GEMS Using the First Integrated Data Model
More LessGEMS/Fastrack is an application used by prospect evaluators and portfolio analysts to assess the
volumetric potential of subsurface resources and to manage their portfolios.
The HC volumes calculated in Fastrack are used to report udSFR and dSFR volumes (undiscovered- and
discovered Scope-For-Recovery, respectively) and Business Case volumes, the latter being an
important prospect-ranking criterion to determine which prospects will be matured.
All computation results are stored in an Oracle database that makes use of an integrated data model
meaning that the same database holds the coordinates of the target and prospect outlines as well as
the non-spatial data, i.e. all other data. The integrated data model imposes a common key between
the spatial and non-spatial data. This enables easy checking of consistency between the spatial and
non-spatial data and allows for spatial querying of the database through a Geographical Information
System (GIS). Apart from volumes, reservoir input parameters such as GOC, OWC, GWC and length of
oil and/or gas column are also available. These parameters are not only used to rank the prospects but
also to quality control the data.
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3D Microanalysis of Geological Samples with Nanofocus Computed Tomography
Authors Gerhard Zacher, Jens Lübbehüsen, Oliver Brunke and Thomas MayerDuring the last decade, Computed Tomography (CT) has progressed to higher resolution and faster
reconstruction of the 3D-volume. Most recently it even allows a three-dimensional look inside of
geological samples with submicron resolution. This allows sophisticated analysis of hydraulic
parameters like porosity and permeability or volumetric information about distribution and quantitative
content of specific minerals providing important information for petrophysicists.
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Remote Sensing-in-Aid to Geo-Scientists
Authors Siddiq H. Al Balushi, Issa S. Quseimi and Ahmed S. TabookOver the years the use of Remote Sensing (RS) in Petroleum Development Oman (PDO) has evolved
from being seen as providing general surface information images for seismic and engineering planning
activities to an essential and cost effective tool to support many other added value E&P activities. With
the increase in the number of Satellites and their spatial resolution and different type of sensors;
accurate and detailed images can be acquired at a lower cost; this opened up new applications for Oil
industries including high accuracy surface deformation monitoring. Satellite images /data and Aerial
photos are used to provide overview of the regional geological setting, pre-and post plan 2D and 3D
seismic surveys, engineering construction activities, selection of exploration well sites, monitoring
environmental impact and pipeline transfer of hydrocarbons.
This paper demonstrate the varied application used in oil and gas activities including Surface
Deformation Monitoring and Enhanced Oil Recovery (EOR) projects in support of reservoir surveillance
and geological modelling.
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Fast Appraisal and Maturation of Heterogeneous Carbonate Fields in a Shuaiba Stratigraphic Play, North Oman
We present two case studies discussing the synergy between appraisal and maturation activities of a
heterogeneous carbonate play in North Oman. Key aspects are the effects of the complex geology on
how quickly new fields can be brought on stream after discovery.
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Variations in Formation Water Salinity and Its Bearing from Oil API in a Shallow Heavy Oil Bearing Sandstone Reservoir in Ratqa Field, North Kuwait
Authors Kawthar I. Sultan, Arshad Aziz, Sawsan Al-Zanki and Abdul Ridha Al-AshwakThe extensively drilled, Lower Fars Formation of Miocene age, hosting heavy oil in the Ratqa Field of
North Kuwait, comprises alternations of fluvial to estuarine channel sands and associated overbank
shales, ranging in depth from 260 feet in the South to 550 feet in the North, capped by a shale,
considered the regional top seal. The formation thickness ranges from 750 feet in the South to 900
feet in the North. The sands are disposed along a relatively gently sloping SW-NE structural monocline,
without any observable structural or stratigraphic entrapment. Large variations in formation water
salinities have been observed from well testing and from log derived estimations. Presence of very low
salinity water at shallow depths of 200-300 feet and enormous increase in the salinity with depth, at
places, indicates possible contamination of formation water having over 100,000 ppm as NaCl
concentration, with a relatively fresh water.
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Detailed Compositional Modeling of Gas Injection Pilot in Giant Carbonate Reservoir in the Middle-East
Authors Tawfiq A. Obeida, Adrian Gibson, Bikram Baruah and Hussain Al HashemiThe objective of this paper is to address the main challenges that have been encountered in the
simulation study when using local grid refine (LGR) within upscaled models. The challenges are mainly
due to the unreliability of populating the fine grids with reservoir properties and attributes.
Dynamic modeling of a pilot is an important task to predict fluid flow and reservoir behavior which is a
major step of pilot design. Dynamic models usually have many limitations when it comes to geological
description due to upscaling of fine-grid static model.
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Sea-Level and Paleoproductivity Changes Recorded in Early Paleogene Deposits in Jordan: Events for Regional Correlation
Authors Elisa Guasti and Oscar A. AbbinkThe importance of hydrocarbon in the Middle East is well known. However there are still areas where
the exploration potential is not fully developed yet, such as in Jordan.
The Paleocene-Eocene depositional record in the Middle East and North Africa is dominated by
hemipelagic marls that form important seals for petroleum accumulations in certain areas, and by
shallow water limestones which represent good reservoirs, such as the Wafra field between Kuwait and
Saudi Arabia.
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Characterization of the Hercynian Unconformity, for Prospect Evaluation, Saudi Arabia
Authors Sulaiman L. Al-Sulami and Mohammed AmeenThe Hercynian unconformity in the Arabian plate (Late Devonian to Early Carboniferous) impacts the
hydrocarbon resources and therefore is an essential aspect of prospect evaluation and field
development. We conducted a regional characterization of the unconformity using an integrated,
multidisciplinary method, including borehole images, dipmeters, open-hole logs, cores, seismic data,
VSP, inorganic geochemistry and palynology. The study included 13 key wells with over 14,000 ft of
borehole images (across the unconformity) and several hundred Km of seismic sections across key
prospects and traps.
The study shows the unconformity is manifested in distinct modes in terms of:
1. Unconformity facies: including conglomerate/breccia, paleosols, and disturbed zones due to soft
sediments deformation.
2. Angular discordance: including change in dip azimuth, or dip angle, or both.
3. Occurrence of tectonic faults.
The above aspects of unconformity modes offer different hydrocarbon configurations. These include
positive configurations that facilitate a sealing effect, potential reservoirs, or potential paths for
hydrocarbon migration. In addition they include negative configurations that result in losses of
potential resources, through weathering and erosion, of potential source rocks and reservoir rocks.
Case studies of these configurations from mainland Saudi Arabia are presented and discussed in this paper.
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Jurassic and Cretaceous Carbonate Geology and Stratigraphic Plays in the Rub’Al Khali Basin, Kingdom of Saudi Arabia
Authors Craig Harvey, Abdul-Hameed Azzouni and Henk DrosteThe South Rub ‘al Khali Company Ltd is an Incorporated Joint Venture between Shell Saudi Ventures
Limited (50%) and Saudi Arabian Oil Company (50%) and was set up in order to explore for nonassociated
gas in the South Rub ‘al Khali Basin as part of the Natural Gas Initiative in the Kingdom of Saudi Arabia.
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Sweet Success in Sour Arab Reservoirs - How Successful Coring Improved Data Integration
Authors Andreas Briner, Abdul-Hameed Azzouni, Conxita Taberner and Brent WignallThe South Rub' al Khali Company Ltd. (SRAK) is an Incorporated Joint Venture between Shell and
Saudi Aramco and is engaged in exploring for non-associated gas and liquids in parts of the South Rub'
al Khali Basin. The licence area contains significant quantities of ultra-sour gas in the Jurassic Arab Formation reservoir.
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The Role of Non-Seismic Methods in ear-Surface Solutions: Applications of Seismic-Gravity Joint Inversion and Redatuming in South Rub Al-Khali, Saudi Arabia
Onshore seismic data from the Middle East are adversely affected by near surface and intermediate
depth velocity anomalies. The correct estimate of the near-surface velocity field is fundamental to
obtain reliable seismic images. Conventional velocity model building workflows based on refracted
arrivals (i.e. First Breaks - FB) fail to appropriately reconstruct the shallow velocity complexities in the
presence of large velocity inversions, sharp lateral velocity changes and noisy FB. In such cases, the
integration of seismic with additional geophysical measurements (i.e. gravity-EM) can solve the shallow
velocity modeling problem. Simultaneous Joint Inversion (JI) is an elegant and analytic method to
address geophysical data integration. It is implemented in this paper for velocity model building in
South Rub Al-Khali by taking advantage of the availability of high-resolution gravity data coincident
with the seismic acquisition. The analyzed 2D seismic lines are sampling different near-surface geologic
conditions such as dunes, sub-cropping carbonates and karsts. This corresponds to various degrees of
complexity in the near surface velocity field and related distortions introduced in the seismic image
when a conventional “statics” approach is used. An alternative approach to statics solutions is then
explored by simultaneous JI of FB and gravity data residuals for the shallow velocity and density fields.
Pre-stack wave-equation redatuming (WED) is then used to model and remove the effects of complex
velocity patterns from the seismic data. Various degrees of improvement are obtained with the
discussed workflow depending on the severity of the near-surface velocity complexities and shallow
geologic conditions. The analysis of the results allows to identify specific roles for non-seismic methods
for the solution of near surface problems in land seismic data processing.
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Paleozoic Clastic Systems, Reservoir Quality, and Play Mapping in the Rub’ Al Khali Basin, Kingdom of Saudi Arabia
Authors Michael Hulver, Abdul-Hameed Azzouni and Craig HarveyThe South Rub ‘al Khali Company Ltd (SRAK) is an Incorporated Joint Venture between Shell Saudi
Ventures Limited (50%) and Saudi Arabian Oil Company (50%), and was set up in order to explore for
non-associated gas in the South Rub ‘al Khali Basin as part of the Natural Gas Initiative in the Kingdom
of Saudi Arabia.
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Joining the Dots: Cretaceous Prospectivity in the South Rub ‘Al Khali Basin, Saudi Arabia
Authors Michael Moir, Henk Droste, Craig Harvey and Andrew WeedonThe South Rub ‘al Khali Company Ltd is an Incorporated Joint Venture between Shell Saudi Ventures
Limited (50%) and Saudi Arabian Oil Company (50%) and was set up in order to explore for nonassociated
gas in the South Rub ‘al Khali Basin as part of the Natural Gas Initiative in the Kingdom of Saudi Arabia.
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Listening to the Right Thing: The Integration of Low Frequency Seismic Data with Other Geophysical Methods as a Frontier Exploration Tool in the South Rub ‘Al Khali Basin
Authors Colin Nunweek, Michael Hulver and Pieter van MastrigtThe South Rub ‘al Khali Company Ltd is an Incorporated Joint Venture between Shell Saudi Ventures
Limited (50%) and Saudi Arabian Oil Company (50%) and was set up in order to explore for nonassociated
gas in the South Rub ‘al Khali Basin as part of the Natural Gas Initiative in the Kingdom of
Saudi Arabia.
Following an initial three well exploration drilling campaign in SRAK’s Contract Area 2 (CA2), SRAK
embarked on a second major phase of 2D seismic acquisition. Low frequency seismic data has been
acquired on all new 2D seismic lines via an embedded recording set-up. This has resulted in the largest
combined PSTM / LF exploration data sets acquired to date.
One of the key challenges facing low frequency seismic as an effective exploration tool is the lack of
signal depth discrimination. This presentation will focus on the combination of low frequency seismic
with conventional seismic products in order to constrain the depth of the low frequency signal and how
combining these workflows with geologic models has led to the identification of a potentially new
hydrocarbon play in the southern Rub ‘al Khali Basin.
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Where Is My Sand Wedge? Part 1: Exploring for Stratigraphic Trapping Potential in the Unayzah Group, South Rub' Al Khali Basin
Authors Geoff Pike, Craig Harvey, Michael Hulver, Ashraf Khalil and Pieter van MastrigtThe South Rub ‘al Khali Company Ltd is an Incorporated Joint Venture between Shell Saudi Ventures
Limited (50%) and Saudi Arabian Oil Company (50%) and was set up in order to explore for nonassociated
gas in the South Rub ‘al Khali Basin as part of the Natural Gas Initiative in the Kingdom of
Saudi Arabia.
To date exploration for a working Palaeozoic petroleum system has proven reservoir in 4-way
structural dip closure and the presence of mature source rock. The search for gas is focused on the
subtle, off-structure stratigraphic potential of the Unayzah Group, and in particular the Nuayyim
Formation and/or Jawb Member sandstones.
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Where Is My Sand Wedge? Part 2: Lessons from Srak’S First Stratigraphic Trap Test in the South Rub' Al Khali Basin
Authors Geoff Pike, Craig Harvey, Michael Hulver, Ashraf Khalil and Pieter van MastrigtThe South Rub ‘al Khali Company Ltd is an Incorporated Joint Venture between Shell Saudi Ventures
Limited (50%) and Saudi Arabian Oil Company (50%) and was set up in order to explore for nonassociated
gas in the South Rub ‘al Khali Basin as part of the Natural Gas Initiative in the Kingdom of Saudi Arabia.
SRAK’s Unayzah Stratigraphic Play exploration has resulted in the identification, de-risking and drilling
of a number of stratigraphic traps in the South Rub Al-Khali Basin. Such traps rely on Nuayyim
Formation (Unayzah A Reservoir Unit) and Jawb Member (Unayzah B Reservoir Unit) targets that
developed preferentially off-structure. Exploration for these stratigraphic traps is generally difficult as
even good quality 3D seismic data cannot resolve subtle facies changes and faults that may be
fundamental trapping components. On 2D seismic, such problems are enhanced and exploration
therefore relies much more heavily on good geological models coupled with geophysical or geochemical
direct hydrocarbon indicators (DHI’s). SRAK tested the largest known stratigraphic trap in its acreage
with its sixth well. Critical to the evaluation and de-risking were a sound geological model from
analogues in the Saudi Aramco Reserved Area, an up-dip calibration well and a world class, 600 km
low frequency seismic (LF) dataset to de-risk the trap.
The presentation will discuss the lessons from the current drilling campaign including an update to the
geological model for the Unayzah Group for the southern Rub ‘al Khali Basin. The application of low
frequency seismic techniques to de-risking has been tested by the drill-bit for both conventional and
unconventional traps and this new technology will be discussed.
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“Brighter than the Moon” - Illuminating the Hydrocarbon Prospectivity in the South Rub' Al Khali Basin
More LessThe South Rub Al-Khali Company Ltd is an Incorporated Joint Venture between Shell Saudi Ventures
Limited (50%) and Saudi Arabian Oil Company (50%) and was set up in order to explore for nonassociated
gas in the South Rub ‘al Khali Basin as part of the Natural Gas Initiative in the Kingdom of Saudi Arabia.
In order to achieve its objectives within the timeframe of the First Exploration Period, a play-based
rather than prospect-based exploration strategy had been devised during the start-up of the Venture to
maximise the chances of identifying working hydrocarbon systems and to optimally position the
Company for a Second Exploration Period.
This encompassed a two pronged approach pursuing pre-Khuff Formation sweet gas prospectivity in
SRAK’s Contract Area 2 in Southwest Saudi Arabia and Khuff and Arab Formation sour gas
prospectivity in SRAK’s Contract Area 1 in Southeast Saudi Arabia. A concerted Technology effort was
made to help polarize drilling opportunities.
As SRAK’s First Exploration Period is drawing to a close in mid-2010, this paper will summarise the
exploration results, review how the exploration strategy evolved through time in response to early
exploration results and distill learnings applicable to similar frontier exploration ventures elsewhere.
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West Esh El Mallaha Concession Fields, Pre- and Syn-Rift Multi-Oil-Bearing Reservoirs as a Structural and Stratigraphic Model in the Eastern Desert Onshore Southern Gulf of Suez Rift Province, Egypt
More LessThe Gulf of Suez is a failed extensional rift basin. Rifting initiated during Early Miocene time and
reached its peak at the end of Burdigalian. Three major fault trends are observed in the Gulf of Suez;
rift parallel or clysmic. North oblique and rift orthogonal cross elements. The Gulf of Suez rift is divided
into three dip provinces separated by two transfer zones. Each dip province has its own geologic
characteristics which makes the hydrocarbon trapping mechanisms are different from one province to
another. The southern province is dominated by SW dipping pre-rift sequences and characterized from
the central and northern parts by more severe extension, faults are more frequent, smaller structural
block size, thicker sand reservoir accumulations during in the Miocene syn-rift sequences, thinner prerift
sequences and well developed Miocene salt diapers. As a result, the southern GOS province is more
favorable for Miocene and Pre-Miocene (including the Basement rocks) hydrocarbon traps. West Esh El
Mallaha concession has oil production from three separate structural closures (Tanan-Tawoos, Rabeh
and East Rabeh). Its total area is 52 km square with 45 wells have been drilled in the concession.
The structural style of West Esh El Mallaha fields are dominated by tilted fault blocks bounded by NWSE
oriented normal, down to the northeast faults and dissected by oblique and orthogonal faults.
Reservoirs range in age from Cretaceous to Miocene.
The first commercial hydrocarbon in West Esh El Mallaha concession was discovered by Coplex in 1997
from Rabeh field. The discovered oil was placed on production on February 1998. Currently, the West
Esh El Mallaha concession fields are operating by LUKOIL/ESHPETCO joint venture company. The
concession cumulative oil production as of June, 2009 is 27.5 MMB, of which 90% is produced from Pre
-Miocene Nubia and Matulla Fms and the remaining 10% from the Miocene reservoirs Nukhul and Rudeis.
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Sequence Stratigraphic Analysis of the Ratawi Shale Formation: Implications for Reservoir Distribution and Exploration Potential in Kuwait
Authors Saifullah K.Tanoli and Mohammad Dawwas Al-AjmiThe Ratawi Shale Formation is first Cretaceous dominantly clastic unit which overlies a thick carbonate
succession in Kuwait. The formation is divisible into three informal zones; the lower one consisting of
mainly shale with limestone interbeds. This part was deposited under transgressive conditions in
shallow marine to offshore environments. An MFS is recognized near the top of this zone which follows
a variable thickness, usually thin, highstand interval due to incision during the overlying lowstand. The
middle zone of the formation consists of better sandstone facies. It was deposited in fluvial to estuarine
environments representing sedimentation in incised valleys in western part and in nearshore to shallow
marine environments eastward. This zone makes the lowstand deposition and completes one 3rd order
cycle of deposition. The overlying upper zone consists of shale with local thin sandstone, siltstone and
limestone interbeds and is interpreted as deposited under transgressive conditions with or without a
recognizable highstand before its termination by the overlying Pre-Zubair late Valanginian unconformity.
High frequency sequences and important related surfaces such as regressive surface of marine erosion
(RSME), subaerial unconformity (SU) or subaerial exposure surface (SES), subaerial erosion surface
(SERS), shoreline ravinement (SR) or transgressive surface (TS), flooding surface (FS) and possible
existence of basal surface of forced regression (BSFR) were identified and described from the cores.
The RSME is usually sharp and wavy separating the underlying offshore muddier facies from the
overlying shoreface sandier facies. The sequence boundary is marked by exposed surface locally
represented by rooted interfluves and in other areas by the weathered horizons and still in others by
incised fluvial surface. The transgressive surface or shoreline ravinement in one case lies at the base of
tidally influenced channel but usually makes a thin burrowed horizon with the fining and deepening
upward trend. The reservoir facies are variably associated with the falling stage systems tract (e.g.
shoreface sandstone above the RSME), with the lowstand systems tract (e.g. fluvial to estuarine
sandstones) and locally with the transgressive systems tract (e.g. tidal channel above SR). An insight
of the sequence stratigraphic set up along with paleoenvironmental regime is crucial for identification
and distribution of reservoir facies in this formation.
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Early and Charge Related Diagenetic Controls from Rock Types (Arab C and D Reservoirs, South Rub' Al Khali Basin, Saudi Arabia)
The South Rub ‘al Khali Company Ltd (SRAK) is an Incorporated Joint Venture between Shell Saudi
Ventures Limited (50%) and Saudi Arabian Oil Company (50%) and was set up in order to explore for
non-associated gas in the South Rub ‘al Khali Basin as part of the Natural Gas Initiative in the Kingdom of Saudi Arabia.
The Arab C and D reservoirs in the Kidan Field of the South Rub ’al Khali Basin have recently been the
targets of a well drilled by the SRAK Venture. A total of 350 ft continuous core was obtained to
characterize reservoir properties and interpret key processes controlling their distribution across the
field. Depositional environments and early diagenetic patterns provided the template for burial and
charge-related modification of rock properties. Distinct reservoir rock types have been differentiated
based on petrographic observations, core porosity, core permeability and MICP (mercury injection
capillary pressure) data.
This presentation focuses on the results of the detailed diagenetic and geochemical study that allows
the interpretation of the key processes controlling the differentiated rock types in Arab C dolostone
units and Arab D ooid grainstone units. Dolostone reservoir properties in the Arab C are mainly
controlled by the presence/absence of late calcite and / or late anhydrite plugging of intercrystalline
porosity. The key diagenetic processes recorded in rock types from Arab D grainstones are: early
cementation, compaction, burial cementation (including calcite, fluorite and anhydrite), late leaching
and late charge-related cementation (calcite and saddle dolomite).
The rock types are mostly stratigraphically defined units, in spite of the recorded complexity of
diagenetic processes, associated diagenetic products and pore size distributions. The stratigraphic
arrangement of the rock types in the studied core responds to depositional and early diagenetic
controls. The late diagenetic products follow the early diagenetic template, nevertheless understanding
the impact of late diagenesis has proven key to predict the rock properties across the field and
construct new reservoir models.
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Wavelet Consistency Assessment for Quantitative Interpretation - A Case Study from Northeastern Saudi Arabia
Authors Ming-Ren Hong, Mohammed Alfaraj, Jinsong Wang and James RiceAn onshore exploration 3D survey located in Northeastern Saudi Arabia and covering an area of
approximately 6300 square kilometers was acquired in 2003. There are two existing oil fields with
Upper Jurassic, carbonate reservoirs controlled by four-way closures, located within the survey.
Current exploration activity, away from these fields, is concentrating on stratigraphic plays involving up
-dip truncation of regional trends with the hydrocarbon seals being created by dolomitization and
cementation within the reservoir.
A multi-well feasibility study confirmed that porosity changes within the reservoir at these seal
boundaries could be seen using acoustic impedance inversion. One important question on the use of
seismic inversion over this large of an area was the wavelet stability. The inversion software used in
the project employed a multi-well, multi-trace approach that allowed for very detailed, thorough and
semi-automated procedures for conducting a wavelet study.
This paper will present the results from wavelet stability tests including analysis of seismic data only by
means of a Markov chain Monte Carlo (MCMC) simulation technique. This is followed by scenarios with
different combinations of single and multiple wells and seismic data, with varying number of traces
around each well used in the calibration and wavelet extraction. The final wavelet determined in the
inversion analysis was then cross-checked among the various techniques. This thorough procedure
confirmed that the wavelet was zero phase and SEG negative polarity, and that it was reasonably
stable throughout the survey.
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Shaybah 3D Amplitude Inversion with Interbed Multiple Modeling
Authors Ming-Ren Hong, Harun Mohd Noor and Mahmoud HedefaAmplitude inversion has been used routinely throughout the industry to help assess the reservoir
quality and derive reservoir properties such as porosity. In cases where interbed multiple
contaminations interfere with the primary reflectivity, the inversion results are questionable unless
interbed multiples can be simulated in the inversion procedure.
In this paper, we demonstrate the use of zero-offset modeling, to simulate interbed multiples,
observed in a 3D seismic dataset, acquired over the Shaybah oil field. We identified the interval from
which interbed multiples were generated and produced a reasonable 3D impedance model for use in
the field’s development drilling program.
A “layer-stripping” type modeling approach was used to identify the interval from which the interbed
multiples were generated. Three key geologic intervals between the surface and the base of the
reservoir were identified as candidates for the starting layer from which the interbed multiples were
modeled. To begin, the shallowest formation of the three was designated as the starting layer.
Synthetic traces with primary and interbed multiple reflections were generated and compared with the
measured seismic data. This procedure was repeated for the deeper two consecutive formations. At the
conclusion of this modeling exercise, it was determined that using the shallowest formation as the
starting layer produced the best match between the synthetic and measured seismic data.
The inversion algorithm used a model-based method where the starting model was generated by
interpolating known log impedances between existing well control based on the interpreted seismic
time horizons. The initial model was then optimized by iteratively updating the impedance to minimize
the error between the synthetic, generated from the model, and the seismic. The final inversion results
were evaluated by matching the measured 3D seismic data to the impedance logs at the wells.
Comparison of seismic and inverted impedance volumes showed that the top of the reservoir was more
clearly defined by the impedance volume; whereas the 3D seismic signature for the top of the reservoir
is poorly defined due to the presence of the multiple interference.
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Exploration Campaign Drilling for Low-Relief Channel-Sand Prospects, South Central Oman
Authors Recep A. Kazdal, Cees van Eden and Lanette MarchaDuring 2009/10, PDO Exploration is executing a ‘peephole’ exploration/appraisal campaign for 2
prospects in the vicinity of a field which was developed using several grid drilling campaigns since
1990. The Field, discovered in 1986, is a low relief anticline (approximately 45m relief and 100 km2
closure) located in central Oman. The oil is produced from the Permian Upper Gharif channel sands,
deposited within a predominantly muddy floodplain and hence with a relatively low net/gross of some
30%. The oil is 24o API with a viscosity of 45cP. Experience, gained during the appraisal and early
development stages of the field, is being brought to bear on the exploration and appraisal of its
satellites. The initial field development was based on the drilling of high-angle, deviated wells aimed at
maximising the chance of finding the fluvial channels. This achieved a low rate of success at a high
drilling cost. A new strategy of drilling multiple, low-cost, vertical wells (peepholes) was implemented.
The economics of this campaign drilling could tolerate the expected low success rate, eventually
improving understanding of the reservoir distribution patterns and reducing uncertainty in targeting
productive sands. The first peephole campaign in the field started in 2001. Twenty wells were drilled
with a success rate of 60%. The ensuing second campaign drilled another 12 wells with a success rate
of 66 %. Both campaigns resulted in a substantial production increase and met both the economic and
geological success criteria. Using this field development as an analogue, 12 wells have been
incorporated on the Exploration drilling sequence to appraise the first satellite prospect. A further 10
wells are planned on a second prospect in 2010. This paper will share the results and learnings of the
first drilling campaign. The first campaign well proved an oil bearing zone with a much higher net/gross
than the historical exploration well.
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Utilising New GIS Tools in Petroleum Exploration and Production
Authors Joerg Mattner and Rajasekar GanesanChallenges for the petroleum industry increase continuously; the “easy” reservoirs have been
discovered and are produced today. New technologies and increasing sophistication, both in the data
display, evaluation and interpretation are utilised to home in on new prospects and increased production.
We show petroleum geoscience studies in which GIS was fundamental in bringing together varied data
sets on multiple scales to accomplish an integrated and result oriented analysis. New tools allow
geoscientists who are not GIS experts to efficiently analyse and interpret a wide range of data e.g. well
data, present-day and paleo-fault leakage and cross-flow probability, reservoir compartmentalisation,
fracture sweet spots, facies distribution and depositional direction. Regional paleo-stress and structural
maps are used to guide and constrain these interpretations.
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Hydrocarbon Charge and Reservoir Pressure History of the Carbonate Stringer Play in South Oman - Implications for Pre-Drill Pore Pressure Risking
Authors Paul N. Taylor, Afifa Al Harrasi, Cees van Eden and Mohammed Al GhammariThe Ara Stringer Play in the South Oman Salt Basin contains sour oil and gas fields reservoired in
carbonate slabs encased within salt. Hydrocarbons occur in a depth range of 2.5 km to 5.5 km with
reservoir pressures ranging from hydrostatic (10-11 kPa/m) to near-lithostatic (22 kPa/m) gradients.
Similarly, in-situ hydrocarbon fluid densities vary widely, from 3 kPa/m to 8 kPa/m. Such variability in
reservoir pressure and fluid density present a challenge for the design of safe and cost-effective drilling
and completion strategies. Of particular concern is the combination of dry gas and hard overpressure,
which could lead to well head pressures of up to 100 MPa (14,500 psi) at 5km. To address this
uncertainty we have completed an integration of reservoir pressure data, seismic data, fluid PVT data
and geochemical data to allow the construction of a model for the risking of likely pressure regime and
hydrocarbon fluid types pre-drill.
Previous work has shown that stringers which have pore pressures close to a hydrostatic gradient
today, should have been highly overpressured prior to a “deflation” event in the geologic past. Our
observations on the hydrocarbon fluid characteristics support a scenario in which gas-condensate
accumulations have originated from a palaeo oil phase within overpressured reservoirs. These oil
accumulations were subsequently depressurised to allow separation and segregation of a gas phase.
In the event that a “deflated” stringer is re-pressurised due to further burial, the saturation pressure of
the mixture will be exceeded once again and the two-phase accumulation will revert back to a single
phase oil column. Therefore highly overpressured gas reservoirs are only expected when the oil and
gas phases are physically isolated prior to re-burial. Structural separation of the oil and gas legs of a
palaeo-accumulation in the Ara Stringer Play has been observed.
The consequence of a phase separation / segregation model of gas occurrence is that the density of
the segregated gas-condensate fluid is dependent upon the reservoir pressure (depth) at the time of
deflation to hydrostatic conditions. There is, therefore, a strong depth dependency to the predicted
fluid character, with in-situ density increasing with depth. This knowledge can be used to optimise
engineering decisions, rather than relying on the “worst-case scenario” of lowest density fluid
properties and highest reservoir pressures observed within the play.
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Offshore Cyprus - A Future Hydrocarbon Player
By Per H. SembOffshore Cyprus, located in the eastern Mediterranean close to the already proven hydrocarbon
provinces offshore Egypt and Israel covers a huge unexplored area. This area has recently drawn a lot
of attention from the oil and gas industry after arranging its first license round in 2007 and from the
news of the very encouraging lower Miocene gas discoveries in offshore Israel.
The Cyprus Ministry recently announced they are ready to launch its 2nd license round around Q4 ’09 -
Q1 ’10 after completion of the first round which resulted in award of one block to the American
company Noble Energy Inc. In the 2nd round all open blocks will be offered, in total 12 blocks, each
with size of 4-6000 sq km which sums up to more than 70,000 sq km of unexplored acreage.
The offshore blocks are covered by more than 19,000 line km of newly acquired 2D seismic and 750 sq
km 3D seismic data. About 12,500 line km of the 2D data was acquired in 2008/2009 with a dual
sensor streamer technology which especially enhances the lower frequencies (also enhancing the
higher frequencies) which is crucial for penetration and imaging of the pre Messinian structures. The
recent acquired 2D seismic reveals a full set of new potential plays offshore Cyprus. In the thick pre
Messinian sediment package in the Levant basin a lot more details are seen and more of the deeper
low frequent structures are reveled giving a better understanding of the potential plays. The enormous
Eratosthenes structure located south of Cyprus which origin has been subject to a lot of discussion is
now revealing a lot more of its structural elements, supporting the idea of the structure as a potential
hydrocarbon source/reservoir. The western offshore and the Herodotus Basin is in general complex
with a lot of thrusting and faulting were several big 4-way closure structures have been identified
together with a set of interesting pre Missinian fault blocks. Several hydrocarbon indicators as flat
spots, amplitude anomalies and gas chimneys identified both in the pre and post Messinian sediments
further enhance the hydrocarbon potential in offshore Cyprus.
Based on the promising structures and elements identified in the seismic data and the recent Dalit and
Tamar discoveries (0.5 and 5Tcf of gas) in offshore Israel, offshore Cyprus is expected to receive a lot
of attention from the oil and gas industry with regards to the second license round and will be an
important player in the future search for hydrocarbons.
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Tectonic Escape (Indentation) in Central Saudi Arabia, Possibility and Exploration Potential
Authors Mesbah H. Khalil, Muzaiyen E. Muzaiyen, Khalid M. Hmoud and Luay B. IsmailTectonic analysis indicates a high possibility of tectonic escape structures in central Saudi Arabia which
could bear significant hydrocarbon exploration potential. This study aims to introduce a new tectonic
model that explains several surface and subsurface newly mapped structures in central Saudi Arabia.
Potential fields, seismic and surface geology data are integrated to accomplish this study.
Basement terrane analysis of the Arabian shield and its eastern continuation beneath the sedimentary
basin indicates the general north-south orientation with differences in width and composition. It shows
that the maximum crust thickness is in the middle of the outcroping shield with a promontory
extending 200km toward east in subsurface (Central Arabian Arch) where Triassic (Khuff) marine
carbonates overlay the basement directly. The crust shows gradual thinning eastward from this
promontory till the offshore Arabian Gulf. Some terranes show wedging-out and others show narrowing
against the eastern side of the basement outcrops. This pattern suggests the tectonic escape of the
wedging out and narrowing terranes against the competent Afif terrane since the InfraCambrian
accretion of Arabia. The terrane accretion occurred by westerly driven terranes collided against the
thick promontory of the Afif terrane causing dispersion toward south and north through east-west
accommodation zones. Long segments of unusual east-west surface structures (faults and strike of
strata) over the boundaries of the subsurface basement promontory from north and south are thought
to be a dragging of the dispersed terrane fragments at the promontory boundaries. West of these eastwest
zones, deformation is concentrated at the north-south terranes with curved hard link transfer
zones. This InfraCambrian tectonic setting is believed to have been reactivated during Phanerozoic
tectonic phases to express its escape tectonics pattern further-up till outcrops. Re-distribution of the
Phanerozoic stresses at that inherited basement fabric controlled the geometry of the sub-basins and
their filling during extension phases. It controlled also the preferable locations of structural positive
inversion during compression phases to form the fault related fold traps. This approach explains the
diversity of structural styles in the sedimentary cover (compression, transpression, and transtension)
which formed simultaneously during Late Cretaceous compression but with different directions.
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Dual Sensor Seismic Examples from Around the Middle East
Authors Mark Spencer-Jones and Per H. SembNew dual-sensor streamer 2D data have been compared to legacy conventional streamer data
throughout the Middle East (Cyprus, Egypt, Lebanon, Libya, and Saudi Arabia) to analyze the
differences and quantify the improvements in seismic resolution. A comparison of PSTM stacks after
processing through the same flow of the vintage hydrophone data and the up-going pressure field (Pup)
showed in general a higher signal-to-noise ratio and better resolution of the P-up image. Spectral
analyses quantified the amplitude versus frequency level and showed a significant increase of low and
high frequencies. The low frequency enhancement was particularly significant deeper in the sections
with spectacular penetration below the highly reflective Messinian Salt/Mansiyah Formation layers.
The dual-sensor streamer measures the pressure wave field using hydrophones and simultaneously the
vertical component of the particle velocity using motion sensors, overcoming the limitations of
hydrophone-only acquisition systems. Its unique ability to de-ghost signals and to optimize data
quality, not just for one target depth, but for all depths shallow to deep, promises to significantly
improve our customer’s exploration success ratio, well targeting and recovery efficiency. Besides data
quality improvements, the streamer is operationally efficient because it records in one pass, with one
streamer depth, in seas no other system can handle. The technical benefits of this step change are
seen in three key areas: - Enhanced resolution of the final seismic image - Better penetration revealing
deeper targets - Improved operational efficiency. The first two points result from the increased
bandwidth at both low and high frequencies due to removal of the receiver ghost. The third point
results from the ability to tow deeper, which is operationally attractive as weather and operational
noise are minimal and the streamers are better behaved.
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Considerations for Cableless System Development and Deployment on High Production Vibroseis Operations
Authors Robert G. Heath, John Giles and Vlad MayerNext generation cableless land acquisition systems are now in use on seismic crews in various
countries. Such recorders overcome many of the perceived shortcomings of earlier devices which may
have limited uptake for certain applications.
These new systems are characterised by improved levels of source control integration, a wider variety
of remote unit timing capabilities, abilities to perform remote control of ground stations as well as data
QC/status return, and much improved data harvesting techniques.
This paper reviews these newest source control and recorder technologies, and describes how both
passive and active acquisition in Middle East environments can benefit.
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New Insights from Hydrocarbon Prospectivity - Moroccan and Nova Scotian Conjugate Margins
Authors Hamish Wilson and Matt LuheshiEmerging plays in Brazil, Ghana and Morocco have triggered interest in searching for analogue plays in
conjugate margins. Using paired margins is a powerful way to evaluate basins in search of overlooked
plays. Insights gained from the Rockall, Porcupine and Orphan have been used to evaluate systems
and plan exploration programmes.
Interest in Morocco and NS has been triggered by licence activity. Using data/maps across the margin
is vital in understanding the critical synrift and early postrift play systems. The paper is based on work
undertaken for OETR in Halifax and studies completed on the Moroccan margin. Both margins show
that when integrated into play analyses there is potential for significant volumes of hydrocarbons. The
use of conjugate margin analysis is critical in developing models for de-risking hydrocarbon prospectivity.
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Remaining Exploration Potential of the Paleozoic Section in Abu Dhabi
More LessThe pre-Khuff principal reservoir, Unayzah formation consists mainly of distal braid plain sandstones
with minor aeolian deposits. Facies controls on reservoir quality are weak. Quartz cement, Illite and
compaction are the main causes of reductions in reservoir quality in the Unayzah. Quartz cementation
tends to be most severe in the cleanest, coarsest sandstones and near certain fractures.
Paleozoic seals are provided by the Basal Khuff Clastics, tight basal Khuff carbonate and Middle Khuff
Anhydrite. The base Khuff carbonate seal does not appear to be regional extensive, but localised and
potentially prospect specific. However, there are insufficient data to accurately define the seal for the
Unayzah hydrocarbon accumulations.
The main challenge that faced the Paleozoic source evaluation and basin building was the presence of
few deep well penetrations. Therefore, much of the unknown source and tectonic information were
derived from the surrounding countries. This comes from understanding the regional tectonics and
depositional trends of the southeastern Arabian plate, which helped extrapolate the source trends into
the Abu Dhabi area.
The Silurian source rocks basin modeling was constructed to define the timing of hydrocarbon charge
from this source rocks. Also, the objective of this modeling was to gain an understanding of how the
Paleozoic hydrocarbon system works and, specifically, comparing the timing of hydrocarbon charge
with the timing of fields structural growth history. The basin modeling work of the Silurian Hot Shale
source rocks started by building an extensive database, which includes the information related to
source rock distribution, heat flow of the basin and the construction of the stratigraphic and the
lithological models. Additional inputs such as tectonic events and estimating the magnitude of the
removed section, during the erosional events, were added.
The current maturation modeling indicated that oil from Silurian source rocks was generated early in
the basin history and was widespread by the Late Triassic (220 Ma). Significant gas was present by
Lower Cretaceous (140 Ma) and dominated the hydrocarbon system by Middle Cretaceous (110 Ma).
Significant high mature gas was generated in the early Tertiary (50 Ma). At present-day, charge is still
active in the north of Abu Dhabi.
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Petrophysical Properties Evaluation of Tight Gas Sand Reservoirs Using Integrated Data of NMR, Density Logs and Scal
More LessMany tight formations are extremely complex, producing from multiple layers with different
permeability that is often enhanced by natural fracturing. The complicity of these reservoirs is
attributed to a) Low porosity and low permeability reservoir and b) The presence of certain clay
minerals like illite, kaolin and micas in poress. Evaluation of tight gas sand reservoirs represents
difficult problems. Determination of petrophysical properties using only conventional logs very
complicated. Nuclear magnetic resonance (NMR) logs differ from conventional neutron and density
porosity logs, NMR signal amplitude provides detailed porosity free from lithology effects and
radioactive sources and relaxation times give other petrophysical parameters such as permeability,
capillary pressure, the distribution of pore sizes and hydrocarbon identification. Using of NMR in
individual bases or in combination with density log and SCAL data provide better determination of
petrophysical properties of s tight gas sand reservoirs.
This paper concentrates on determination of three petrophysical parameters of tight gas sand
reservoirs: First, Determination of detailed NMR porosity in combination with density porosity,DMR. It
is found that DMR porosity method is a gas corrected porosity, and independent facies porosity model,
Second NMR permeability, KBGMR; it is based on the dynamic concept of gas movement and bulk gas
volume in the invaded zone. It is concluded that KBGMR is facies independent technique and this is the
most important value of this technique and Third Capillary pressure derived from relaxation time T2
distribution and then it could be used for formation saturation measurements especially in the
transition zone. It is found that the assumptions of capillary pressure approximation from T2
distribution can be applied in gas wells as well with some consideration due to gas and mud filtrate effects.
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Co-Krigged Porosity Modeling Exhibits Better Results than Conventional Regression Analysis and Multiattribute Transform Porosity Models
Authors Amjad Hussain and Aamir RasheedReservoir heterogeneity characterization is always a real challenge for the sub-surface professionals.
Although there is no direct way to assess the true heterogeneity, still certain models can imitate the
important features of variability. The spatial distribution of reservoir properties can be determined by
stepping through a workflow which starts where standard workstation seismic and geologic
interpretation ends. In order to obtain the most accurate and detailed results, one must design a
multidisciplinary workflow that quantitatively integrates all the relevant sub surface data. This paper
demonstrates the enhanced results of regression analysis and the multi-attribute transforms which are
used for porosity prediction in one of the areas in Middle Indus Basin. The co-kriging method used in
geostatistics has been applied to derive a combined effect of both the techniques. The dataset used for
this study consists of the available well data including VSP & the petrophysical logs, a 3D seismic
volume consisting both reflectivity & Inversion data for attribute extraction. A conventional regression
analysis using the single polynomial function incorporating the AI & the well porosities were used to
extrapolate the average porosities away from the known control points. We then applied the multiattribute
transform using various seismic attributes and the well data. A cross-validation of porosity
with the significant seismic attributes was done through neural networking. The results were then
applied to derive initial porosity map. Both the results were integrated using co-kriging approach which
involved creation & comparison of different variograms to get the enhanced version of porosity model.
The co-kriged porosity maps showed a better delineation of good porosity zones as compared to initial
porosity maps.
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Gas Log Monitoring - Challenges and Uncertainties in Gas Injection Pilot in Carbonate Reservoir - A Case Study in UAE
Authors Mostafa Amin, Omar Al Jeelani and Halima Al MansouriThe field under study is Lower Cretaceous anticline carbonate reservoir in onshore Abu Dhabi, UAE. It
is characterized by well developed porosity but low to moderate permeability, occasionally, with high
permeability streaks. The field structure is highly faulted; consequently, many reservoir layers are
juxtaposed due to faulting which have a significant role in the reservoir’s performance. Pressure
maintenance is supported by peripheral water injection. Two gas injection pilot projects are underway
to investigate the benefits of gas injection above MMP (Minimum Miscibility Pressure) in the low
permeability reservoirs.
As part of the field development a peripheral water injection scheme is in place, and two gas injection
pilots were commissioned for injection in the entire reservoir.
The purpose of this work is to:
- present an overview on the implemented strategy for log monitoring in sense of the logging types,
logging timing and the interpretation techniques;
- summarize specific actions taken to gather log data;
- discuss and evaluate the field observations; and
- address the challenges and uncertainties of monitoring process.
The results of the monitoring observations in this work are being incorporated into simulation studies
for a conclusive assessment of the pilots.
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Remote Control: Well Control - Production and Drilling
By Amit MehtaAs processor speeds double and triple machines are becoming smarter to guide human actions vs. the
other way. The key to enable machine dictating human actions resides in ability of humans to ensure
machines have all the necessary data no matter where it resides in corporate systems to guide its
actions. Moblize has come up with a mechanism where each machine with a CPU can be exposed as a
web service not only talk directly to data residing in corporate databases but also to machines in its
vicinity for most up to date information. On this basis, we can today enable unmanned platforms in
production to control chokes. How does it work? Based on input the machines receive from nearby
disparate flow meters on accumulates volumes/flow rates (on a wireless or wired network) and data
from corporate database (historical), the machine can present human with a holistic picture. For
example, imagine an event flow rate is high but storage is an issue, so we should turn the choke by
say 1/64th of an inch in close position to reduce flow rate. The human can then review the result and
according to the over secure web connection manually change the choke positions from Integrated
Operations Center with a click of button vs. a personnel going on a boat to the physical platform and
doing the same, which creates concerns on safety and increases costs. So essentially, we have a two
way mechanism where our software can take machine language and output it as web service or take
web service and input it as machine language. It also provides humans the ability to write small
snippets of code which can be houses anywhere on a network and depending on variety of sensor
inputs like pressure/temp/flow rates automate the control of choke without human intervention if desired.
Drilling: The same concept is being exploited in the drilling arena, where clients can virtually use our
software to control top drives, flow rate of mud, steer drill, and many new concepts we are trying to
pilot and test. Our software has a proprietary mechanism to talk in machine language to the top drives,
in this case, and expose them as an internet service and render them as a smart service. The user
based on variety of inputs from the top drive and other relevant sources (data sources) could control
the top drive or other machines from integrated center remotely.
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New Generation Seismic (NGS) Acquisition with a Land Seismic Super Crew
Authors Said Mahrooqi, Said Abri, Saeed Yarubi, Awadh Yahyai and Paul MathenyIn 2008, Petroleum Development Oman implemented New Generation Seismic to fulfil technical
objectives while taking into account economical and efficiencies factors. The technical objectives are to
obtain properly sampled and wide azimuth (WAZ) seismic for both shallow and deep objectives in
support of current and future exploration and development projects. The sampling requirements to
meet these objectives translate into receiver grids of 12.5 to 25m in-line by 200m maximum cross-line
and full source VP grids no less than 400 VP/km2 (for example 50x50 m or 25x100 m). The WAZ
requirement is to provide a minimum offset in all azimuths of at least the depth to deepest perceived
target (typically 4km or greater). When combined, these sampling and width requirements result in
New Generation Seismic with a fold exceeding 4000 in 25x25m bins suitable for full Common Offset
Vector processing and full azimuth interpretation and quantification of azimuthally varying seismic
attributes. Further, full top to bottom and high quality imaging is realized for both very shallow and
very deep targets.
In order to efficiently acquire large areas, 10000+ km2, with over 400 VP/km2 two super crews were
introduced. One super crew with a capacity of 25,000 channels (12 Geophone per station), and 16
vibrators, and the other with 16,500 channels (also 12 Geophones) and 16 vibrators. These super
crews enable efficient operations with block widths in the range of 30+ km (a 30% efficiency
improvement), and also fully productize dual methods of short sweep length simultaneous sourcing
using both slip-sweep and distance separation (a 300% productivity improvement). In addition, the
super crews now operate 24 hours per day (another 50% productivity improvement) and are equipped
with the latest high channel count and high productivity SN428 recording system and VE464 vibrator
electronics. While the throughput of these super-crews is approximately a factor 6 improved, the
number of people needed in the field is a much more modest increase of approximately 50%.
As fully implemented in 2008, these super crews are consistently meeting PDO expectations and are
setting world record productivity numbers. Daily average VP rates exceeding 13000 are common.
Considering PDO’s minimum VP density of 400 VP/km2 these productivity numbers translate into an
average production of 30+ km2 surface area per day per crew.
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Miqrat Formation (Cambrian) a Challenging, Tight Gas Play in Prograding Sheetflood Sands, Sultanate of Oman
Authors John Aitken, Fryberger G. Steven, Uzma Mohiuddin, Abdullah Al-Hakmani and Bernard BeslyThe Miqrat Formation (middle Cambrian, Haima Supergroup) of North Oman is an identified deep, tight
(low permeability) gas reservoir that was deposited in an arid to semi-arid continental setting,
consequently it is biostratigraphically barren. It is dominated by finely interbedded, red-brown shales
intercalated with argillaceous and feldspathic/micaceous very fine- to fine-grained sandstones and
siltstones. These were deposited in alluvial and playa/lacustrine to sabkha environments with minor
aeolian intervals. The formation offers a variety of geological and well engineering challenges, largely
related to its depositional setting and age.
Facies relationships were controlled by a spectrum of sedimentary processes operating at different
scales. Important constraints, at a basin scale, are wet/dry climate cycles within a framework of
varying sedimentation rates and accommodation space. Developing accurate subsurface depositional
models is hampered by poor seismic resolution and a lack of reliable correlation events to constrain
palaeogeographic reconstructions and tie these to field-scale depositional models. With limited well
control, absence of biostratigraphic markers and non-unique wireline log characteristics, correlation of
similar-appearing sheetflood sands may be erroneous as these may correlate with time equivalent
flood margin or muddy playa deposits. The identification of correlatable markers is, therefore,
significant. Pilot studies applying chemostratigraphy suggest that this technique may prove to be a
useful tool for subdividing the Miqrat Formation.
Regional and in-field Miqrat well data, integrated with outcrop studies, provide the main input into
geological models and the basis for play maps and static reservoir modelling. However, many
challenges exist, especially for early appraisal activities. These include reservoir productivity
identification and “sweet-spotting”; assessment of gas mobility during drilling; petrophysical evaluation
(saturation/mobile phase identification). Additionally, the role of fractures needs to be understood in
achieving commercial rates, whilst fraccing and testing require innovative solutions to provide optimal
stimulation and reservoir assessment, respectively. Project attractiveness may rely on improvements in
seismic imaging, improved play models, better prediction of reservoir quality/fracture networks,
together with a better understanding of charge history and improved offtake rates.
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The Upper Triassic Minjur Formation: A New Bio- and Sequence Stratigraphic Framework and Its Implications for Hydrocarbon Prospectivity
Authors Neil S. Jones and Nigel P. HookerThe Upper Triassic (Norian to Rhaetian) Minjur Formation is a siliciclastic succession present at surface
and also in the subsurface across large parts of central and southern Saudi Arabia. Until recently its
stratigraphy and sedimentology have been poorly understood and it has largely been ignored as a
target for hydrocarbon exploration. A recent study by the Area Exploration Department of Saudi
Aramco built a regional bio- and sequence stratigraphic framework to support regional exploration
efforts in Central Arabia and better understand its prospectivity. This study utilizes core and cuttings
data from 26 wells, combined with wireline logs from an additional 100 wells. It should be noted that
all 600 ft of available Minjur Formation core in Saudi Arabia was studied.
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Geology Meets Petrophysics: from Example of a Process-Based Rock Type Methodology for a Khuff Reservoir, North Oman
Carbonate reservoirs are inherently heterogeneous as result of being deposited in laterally variable
settings with subsequent overprint of complex and substantial diagenetic processes. The Upper Khuff
carbonate reservoir, deposited on a large carbonate/evaporitic ramp (Late Permian - Early Triassic), is
a prime example for such reservoir quality variability dictated by its intrinsic carbonate nature.
A Rock Type (RT) “process-based” geological-petrophysical approach has been applied to a Upper Khuff
reservoir in North Oman in order to improve the reservoir characterization and the understanding of its
heterogeneity, and ultimately to derive representative static and dynamic models. This approach is
based on the integration of sedimentological/petrographic core observations and the analysis of
petrophysical properties in wells.
A core-based Rock Type scheme was defined based on Porosity/Permeability from CCA, pore type
identification and sedimentological observation on thin sections. Each RT was linked to the original
depositional facies and the subsequent diagenetic processes (cementation, dissolution, dolomitization,
anhydrite precipitation). Pore throat distribution and capillary pressure curves were also used to
calibrate the classification scheme. RTs with enhanced properties correspond to two classes:
dolomitized oolitic-skeletal Grainstones and Thrombolites (with intercrystalline, interparticle/mouldic
and vuggy porosity) and oolitic/peloidal/skeletal Grainstones and Packstones (with mouldic,
interparticle and vuggy porosity).
A Neural Network approach was used to implement this RT scheme to all wells, and its results were
calibrated to cores. An electro-facies log was obtained by combining Gamma Ray, Porosity and BVSxo
logs. This results in a ‘Depositional Facies’ log, comprising: Bioconstructed facies, Grainstones (well
and poorly sorted), Packstones to Mudstones and Argillaceous Mudstone. The ‘Lithology’ log was
generated from the Gamma Ray, Neutron/Density and PE logs to distinguish amongst Limestone,
Dolostone, Anhydrite and Argillaceous Mudstone. The final RT log was generated by merging
‘Depositional Facies’ and ‘Lithology’ logs.
‘Depositional Facies’ and ‘Lithology’ logs were used to build 3D Facies properties (Depositional Facies
and Lithology). The latter were directly merged to generate RT models. Porosity and Permeability were
modelled conditioned to RTs which resulted in more realistic distributions.
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Evaluation of Petroleum Generation Potential in Qom - Ardestan Structural Zone in GIS Environment by Fuzzy Method
Authors Marjan Roosta, Nader Fathianpour and Jalil SadouniDue to concentration of petroleum potentiality studies in south and southwest of Iran, It is necessary
to evaluate the potential of other areas especially some parts of Central Iran which have thick
sedimentary strata and sometimes organic matter potentiality (e.g. Qom, Shemshak formations) and
exploitation possibility from this huge resources to be matter of interest of economic administrators of
the country. Compilation and analysis of all information in a suitable environment and exploration
moulding will lead to assessment of satisfactory petroleum zones for further studies. Therefore, in Qom
- Ardestan Area which bearing high amount of petroleum and gas is explored in here. After studying
the geology of this area, segregation of the area anticlines as trap layer, faults as migration layer and
the whole Qom formation and its prospect member (C3) as reservoir rock took place. In organic
geochemistry discussion, considering three dimensional thermal model, vitrinite reflectance values, and
total organic carbon in different wells in the area, we derived the maturity and geochemical layers. The
result of these researches is preparing 9 information layers including geochemical, geological, maturity,
and structural layers. These layers were integrated by a knowledge based fuzzy method. Modeling
based on this method was made using 22 educational points. The out put was settlement of 100% of
drilled wells in area with high potential in this model. The areas with high potential for further
exploration drilling are defined in the studied area.
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Exploration for Hydrocarbons in a Half-Billion-Year-Old Chert, the Athel Story Continues
In 1989 and 1995, two oil fields were was discovered in South Oman in Athel ‘Silicilyte’ reservoirs,
comprising Proterozoic to Early Cambrian chert slabs encased in Ara salt. The reservoir units have good
porosity but very low permeability and only flow light oil if massively fracc’ed.
When discovered it was thought that the chert layers might be present throughout the region but with
limited drilling success in the 1990’s it became clear that the reservoir was more restricted in
occurrence. A plethora of possible models exist for the origin of the chert and, therefore, it’s distribution.
The play requires that a porous slab of laminated chert be encased in salt, charged with light oil and
that overpressure is maintained. The permeability must be sufficient to maintain long-term flow after
fracc’ing. These constraints together with the reservoir, seal and charge distribution maps help define
the play sweet spot. In order to identify and evaluate likely prospects, high quality 3D seismic is
needed and an extensive seismic acquisition, reprocessing and analysis program is in progress in PDO’s
Block 6. Re-mapping and prospect analysis is being used to update the lead and prospect portfolio and
help de-risk the play. The play-based approach provides a balanced geological and geophysical derisking
scheme with the intent of providing drill worthy opportunities by 2011. This paper presents a
new reservoir distribution model based on integration of previous work, regional well and seismic data
analysis, study of global chert analogues and outcrops in Oman.
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Portfolio Rejuvenation in a Mature Hydrocarbon Province, Sultanate of Oman
The Sultanate of Oman has seen over 50 years of exploration and over 40 years of oil production. The
petroleum systems span over 800 Million years of geological rock record, and over 40 plays have been
identified. It comes as no surprise that most of the structural plays are heavily creamed. PDO
exploration has continued to be successful in this mature but prolific hydrocarbon basin, by sustained
effort and focus on rejuvenating the portfolio. Significant potential remains in stratigraphic traps, deep
plays and unconventional hydrocarbon systems. Technology and play based exploration are seen as
key enablers to deliver this potential.
3D Seismic capabilities within PDO are undergoing a revolution at the moment. An aggressive
exploration campaign acquiring over 8000 km2 of high quality 3D seismic to unlock the potential of pre
-salt and intra-salt plays is underway. The step change in seismic imaging quality combined with new
quantitative interpretation methods are essential components not just in salt related plays but also in
delineating stratigraphic traps within the shallower plays. Alternative delineation methods considered
are also novel drilling techniques and non-seismic geophysical techniques.
New technologies, in combination with regional play based evaluation, have resulted in the
identification and high grading of several attractive new play segments: 1) a thrust faulted play
segment within the yet to be proven pre-salt play, 2) a northwards extension of the prolific intra salt
Stringer play, 3) an extension of the challenging intra-salt Athel silicilyte play, and 4) a stratigraphic
play segment within the Gharif.
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The Usefulness of Light Hydrocarbons in Classifying Oman Oils
Authors Mohamed R. Al Ghammari and Paul N. TaylorIn order to improve the understanding of the origin of light oils, which have low biomarker
concentrations, Petroleum Development Oman (PDO) developed a new classification tool based on the
distribution of light hydrocarbons (LHC). This tool proved useful for identifying mixing patterns
between light oil/condensate and normal medium and low gravity oils. The database for this study
consists of 71 non-biodegraded normal oil/condensate samples from various oil families and sub-oil
families of Oman. All oils/condensates were first classified using C15+ compositions. Various plots and
parameters based on light hydrocarbons composition (LHC) were collected from literature and used in
this study. It is found that the published LHC parameters are very useful tools in classifying Oman oils
(e.g. Schaefer parameters, Halpern correlation parameters). In addition to the published parameters,
Principal Component Analysis was performed on these samples using the C7 composition (22DMP
through to Toluene). Two useful parameters were successfully extracted from the statistical evaluation
that can distinguish between various oil families. These are Total DMCPs/n-C7 and (22DMP+24DMP+11DMCP)/ECP.
Most of the LHC parameters were able to distinguish between four oil families; Huqf, Athel, Q and
Mesozoic (Natih+Tuwaiq) oil families. Each oil family is characterised by a unique LHC distribution.
Huqf oils are generally characterised by higher paraffins and lower cycloalkanes than the rest of the oil
families. Q oils are characterised by higher branched alkanes than the rest of the oil families. Mesozoic
oils (Natih+Tuwaiq) are characterised by higher cycloalkanes than Huqf and Q oils. Apparently, most of
the Natih oils have Tuwaiq input and no single oil sample has been found for pure Natih oil. Therefore,
most of the plots cluster them together. However, one parameter 22DMP+24DMP+11DMCP/ECP was
found to be able to tentatively distinguish between the two oils, Tuwaiq pure oils and Natih/Tuwaiq
mixed oils. Both Natih and Tuwaiq oils are characterised by higher cycloalkanes than Huqf and Q oils.
Only one sample of apparently pure Silurian ‘Safiq’ oil was available for C7 composition. The
composition of this oil was different from the published characteristics of Silurian oils elsewhere in
Arabia. We are not able to determine whether our single oil sample is representative for Silurian oils in Oman.
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The Land-Streamer Acquisition System to Map the Sand Dune Base
Authors Hashim Almalki, Tariq Alkhalifa, Ramzy M. AlZayer and Abdulrhman AlaneziComplex near-surface structure is a major problem in land seismic data. This is more critical when
acquisition takes place over Sand dune surfaces, where the base of the Sand acts like a trap for energy
and depending on its shape can considerably distort conventionally acquired seismic data. Estimating
the base of the Sand Dune surface can help model the Sand dune and reduce its harmful influence on
conventional seismic data. Among the current methods to do so is drilling upholes and using
conventional seismic data to apply static correction. Both methods have their cost and limitations. For
upholes, the cost factor and its inability of upholes to provide continuous model is well realized.
Meanwhile, conventional seismic data lack the resolution necessary to obtain accurate modeling of the
Sand basement. We develop a method to estimate the Sand base from Land streamer seismic
acquisition that is developed and geared to Sand surfaces. Land streamer acquisition not only provides
a more efficient data acquisition system than the conventional spiked geophone approuch, but in our
case the land streamer provided better quality data, with broader frequency bandwidth. Such data
enabled us to do proper near surface velocity estimation that resulted in velocities that are very close
to those measured using uphole methods. This fact is demonstrated on a couple of lines acquired near
upholes, and the agreement between the seismic velocities and the upholes is high.
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Improved Structural Understanding of a Complex Anticline through Advanced Seismic Processing: A Case Study from Northern Iraq
Authors Jürgen Hoffmann, Øyvind Engen, Nils Bang, Jens-Petter Nørgård and Olaus Andreas HarstadThe Tawke anticline is situated in the Kurdistan region of Northern Iraq in the folded zone of the
Zagros fold and thrust belt. The region is characterized by folded Cenozoic carbonates and foreland
basin siliciclastics, with considerable differences in mechanical properties. Rough terrain, narrow
structures and strong velocity contrasts pose significant challenges to seismic imaging in the area.
In 2006, DNO completed the first ever 3D seismic survey in Iraq with the objective of determining the
subsurface structure of the Tawke oil field discovered in 2005. Since then, the seismic data have been
processed 3 times with progressively more advanced techniques to meet geologists’ and reservoir
engineers’ demands for resolution and accuracy.
The first processing involved elevation statics and a fast-track time migration. The main purpose of this
dataset was to perform early volume calculations and well planning. Despite several successful wells,
the data showed clear limitations in imaging of complex thrust structures.
The second processing project was initiated in 2007 using anisotropic prestack time migration based on
the AutoImager velocity model building. This semi-automated method used the initially preprocessed
data as input and provided significantly improved imaging of steeply dipping interfaces and faults. The
key improvement factor was the AutoImager iterative migration velocity analysis producing a
consistent seismic velocity model with anisotropy correction.
Seismic modelling and depth conversion tests were conducted in 2008 using 2D image ray tracing
techniques. Results showed significant ray path bending because of strong lateral velocity contrasts
between Cenozoic carbonates and siliciclastics. This implies that time migration images are inaccurate
and conventional depth conversion by vertical stretching is not applicable. To solve these problems, the
Tawke 3D data were reprocessed using prestack depth migration (PSDM) which migrates seismic
events to their correct positions provided that the velocity model is correct. The PSDM results show
better agreement between seismic events, well logs and VSP data and are consistent with the wider
and gentler top reservoir geometry as predicted by ray trace modelling. Following the startup of Tawke
oil export on 1 June 2009, the PSDM data are used for reservoir management and infill well planning.
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Adaptive Surface Waves Attenuation from Wide-Azimuth Land Data
Authors David Le Meur, Nigel Benjamin, Teo Wah Hong, Tom Van Dijk and Paul MathenyAttenuation of Surface Waves is the first show stopper that is faced in land data processing. However,
the characteristics of Surface Waves, Groundroll and Guided Waves, can be extracted from the input
data themselves to feed a cascaded adaptive filtering in order to remove these troublesome noises.
This approach is done in the FX domain to model the signal and noise. The part of the model
corresponding to the noise is then subtracted from the data using a least squares approach. The
benefit of such an approach is to wipe-out the Surface waves recorded on raw surface seismic data.
This constitutes a technical breakthrough for many difficult areas especially for modern surveys with
Wide-Azimuth acquisition.
The first issues that should be addressed in land processing are the attenuation of Groundroll (GR) and
Guided Waves (GW). Both are Surface Waves recorded on a vertical geophone and are the result of
interfering P and SV waves that travel along or near the ground surface. GR is characterized by low
velocity, low frequency and high amplitude and can be strongly dispersive and aliased. GW are visible
on records as repeated linear arrivals on the longer offsets due to multiple refractions and/or converted
refractions. GW are generated by some specific sub-surface geological conditions such as fast-slow-fast
velocity interfaces at depth and these pollute the long offsets of data with high amplitudes, fast
velocity and higher frequency linear noises than GR but with weaker dispersion. A cascaded application
of an adaptive noise attenuation taking into account the GR and GW characteristics can fully benefit
Wide-Azimuth acquisition and will have a major impact on the S/N ratio and stack response. More of
the acquired data can be utilized to create the stack (e.g. incidence angle might be increased from
25/30° to 40/45°) and this has many positive benefits such as increased accuracy of velocity
interpretation, multiple attenuation, increase in S/N ratio and improved stack response. This paper
focuses on a data driven approach that performs 3D cascaded adaptive filtering of aliased and
dispersive Surface Waves at their true spatial coordinates (AGORA GR & GW) and will be described
using both Narrow and Wide-Azimuth land data examples.
Acknowledgements
We would like to thank Petroleum Development of Oman and CGGVeritas for their permission to
publish this paper.
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Prediction of Apparent Cohesion, Angle of Internal Friction and Poisson's Ratio of Various Types of Rocks Using Laboratory Measured Unconfined (Uniaxial) Compressive Strength
Authors Musaed Al-Awad and Bandar Al-AnaziThe evaluation of Mohr-Coulomb failure criterion as well as other mechanical properties for reservoir
rocks is essential for well planning, development and characterization of oil and gas reservoirs. This is
because the understanding of the rock-stress relationship can solve many reservoir problems and avoid
cost of remedial work. For example, a Mohr-Coulomb failure criterion may be used for borehole
instability analysis, water injection design, hydraulic fracturing design, production optimization
techniques, compaction and sand production prediction, etc.
A Mohr-Coulomb failure criterion is a function of the apparent cohesion and the angle of internal
friction The evaluation of these two parameters requires testing of many rock samples using an
expensive and time-consuming triaxial testing set-up.
In this study, a correlation between the apparent cohesion and the unconfined (uniaxial) compressive
strength was developed. It is based on laboratory data of more than 282 rock samples of different
types obtained from the literature.
The correlation coefficient of the developed correlation equals to 0.88. Verification of the developed
correlation using data from other references has shown an average error of estimation less than 10%.
Unfortunately, some odd predictions were also notices and can be attributed to measurement errors.
Therefore, the Mohr-Coulomb failure criterion’s parameters as well as Poisson’s ratio can be estimated
using the developed correlation based on fast and cheap measurements of the unconfined (uniaxial)
compressive strength.
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Impact of South Oman Salt-Halokinesis from Fault Interpretation
Authors Mohammed H. Al-Kindy and Pascal D. RichardSince Precambrian, Oman region has been influenced by many tectonic regimes that resulted in
different structural styles. The type and amount of tectonics vary significantly across Oman. As a
result, a number of structural domains can be easily defined in south, central and north Oman. The
presence and thickness variation of the underlying Ara salt is one of the key parameters used to define
these domains. In places where salt is absent or very thin, the effect and timing of far field regional
tectonics can be clearly demonstrated (e.g. Lekhwair High). However, in areas where the salt is very
thick, the impact of far field regional stresses is often difficult to distinguish from the local effect of salt
withdrawal and salt dissolution.
In south Oman, salt halokinesis has dominated the deformation style and orientation of local stresses
in Palaeozoic times. This resulted into a tortuous framework of salt domes, ridges and depression
which have influenced any younger deformation events. Initially, sediments were deposited in local
depo-centres (e.g. named as pods) and simultaneous differential loading and salt dissolution is
interpreted to have been the main driving mechanisms of the deformation. It is important to note that
the deformation is happening without external regional far field driving stress regime. The final pod
geometries is directly controlled by sediment supply, space accommodation and initial salt thicknesses.
With ongoing thinning of the salt, the pods grounded progressively. Loci of depo-centres migrated
following the salt availability. The most typical structures formed during this time are turtle-back
anticlines, with extensional faults dipping away from the centre of the anticline. Surrounding these
turtle back anticlines, narrow collapse graben structures have developed above salt ridges/domes
(thick salt area) as a result of salt removal. Across South Oman, a number of depression at the present
surface topography formed above the deep thicker salt area, indicating that salt removal is still
continuous today.
The presentation will concentrate on the early Palaeozoic halokinesis. We will illustrate the regional
structural models with a series of key observations as well as demonstrate how the structural model
can be used to help seismic fault interpretation, especially in area of poor seismic quality.
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Drilling the Longest Horizontal Well in the History of Kuwait Using State of the Art Technologies
The Minagish field, in West Kuwait, is a North-South trending asymmetrical anticline, dipping from east
to west with hydrocarbons contained in six major reservoirs ranging in age from Early Jurassic to Late
Cretaceous. Mishrif is a tight, fractured carbonate reservoir of Upper Cretaceous age developed in a
shallow marine deposition environment. The observed porosity in the upper reservoir layers ranges
between 10-30%. The permeability measured from vertical wells is less than 17 milli Darcy. The
second Mishrif layer is a fairly high porous peloidal packstone to grainstone sequence, composed of
several mechanical sub-layers, mostly fractured and vuggy at the upper 15 feet “dual porosity
system”. Production from this particular layer is related to the degree of fracture clustering, corridors
and open faults which enhancing the permeability of the layer, thereby making it a good potential for
horizontal well placement.
A high geological risk in horizontal drilling is coming from the formation dip uncertainties, which were
expected to vary between 2.5-3 deg upward up to 4-5 deg downward, with an intensity increase close
to the highly faulted areas. Due to the well complexity and uncertainties expected in real time drilling,
the LWD tools selection for the lateral section were based on providing in real time solutions from deep
directional measurements and inversion from the distance to boundary tool primarily and the formation
dip information, fractures and faults identification from the resistivity images. In addition, other tools
selected provide the basic petrophysical measurements such as Gamma Ray, Resistivity and Density-
Porosity logs.
The company achieved a landmark in horizontal drilling with its third Mishrif horizontal well. The
horizontal section at a length of 5312 feet was geo-steered in the sweet spot of the upper- most part
of the Mishrif layer 2 (about 5-10 feet thick) using the most advanced technologies and high-resolution
Q-seismic data.
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Introducing a Priori Information in Non-Linear Slope Tomography: An Application to Minagish Seismic Survey
Slope tomography allows velocity model estimation from locally coherent events. These events can be
picked in the migrated prestack depth or time domains, and then de-migrated into the observation
space-time domain, providing us with kinematic invariant data. When locally coherent events are
picked directly in the observation space-time domain, the kinematic invariants carry the exact
acquisition geometry.
Kinematic invariants describe locally coherent events by their position and slopes in the un-migrated
prestack time domain. Non-linear 3D slope tomography based on the concept of kinematic invariants
provides a powerful tool for velocity model building. Several iterations of residual move-out (RMO)
picking, prestack depth migration and velocity updates are avoided, unlike conventional approaches
based on a linear update where residual depth errors have to be re-picked several times.
Because kinematic invariants do not relate to a particular depth velocity model, a priori information can
be easily inserted into the initial tomography velocity model to assess different geological assumptions.
This capability is illustrated on land Minagish dataset in Kuwait for which RMO has been picked from
prestack time migrated gathers. Tomography and imaging results have been produced for two different
a priori velocity models. A first model was built by 1D Dix inversion of time migration velocities while
the second model was built using velocity information from wells. The updated “wells” model
successfully combines two velocity components: the a priori high vertical resolution component that
cannot be resolved by tomography and a lower vertical resolution component that maximizes the stack
power of the depth migrated seismic data.
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Reduction of Noise Effects from Low Frequency Passive Seismic Data
Authors Brad Artman, Tung Nguyen, Marc Lambert, Stefan M. Schmalholz and Erik H. SaengerAnthropogenic noise effects have always been a great concern for passive seismic because they are
usually strong and difficult to remove. The problem is addressed by analysis of 2D (time-space)
attribute sections derived from the recorded data. On the attribute sections transient noise appears as
isolated points or distinctive linear trends and therefore can be suppressed by common filtering
techniques. We applied the approach on a passive seismic data set from a survey line at an oil and gas
field in Voitsdorf, Austria. The data set is noisy and the presence of hydrocarbon reservoirs could not
be convincingly indicated by conventional analysis techniques. Attribute sections, after being filtered to
reduce noise effects show a good agreement between reservoir locations and high amplitude trends on
the sections. A modelling study reveals that the anomalies observed on the attribute sections match
well with attribute values computed
from synthetic data.
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Imaging Conditions for Time-Reverse Modeling
Authors Brad Artman, Ben Witten and Igor PodladtchikovActive seismic processing is concerned with two-way travel times, down and up, through the
subsurface. In contrast, passive seismic methods are predicated on 3+ travel paths in the case of
interferometry, and one-way travel path wave fields in the case of source location. Secondary sources
and diffractions maintain the same kinematics as primary sources and can also be imaged in the
context of source location. We present the chain of time-reverse modeling, image space wave-field
decomposition, and various imaging conditions as a migration-like algorithm to locate subsurface
sources in passive data and diffractors in active data. The presented imaging conditions respond
differently to source mechanism radiation patterns which interpreted in combination provide more
information than simply location. Passive data examples are developed with surface acquisition
geometry.
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Independent Simultaneous Sweeping in Libya - Full-Scale Implementation and New Developments
At the 2008 and 2009 SEG conventions (Howe et al 2008 and 2009) we reported on a proof of concept
and initial production results of a new acquisition technique called ISS (Independent Simultaneous Sweeping).
This paper describes the successful full scale implementation of this method in Libya after it has been
in use for more than one year acquiring a very large exploration land 3D survey for a project with a
seismic commitment in excess of 13,000 sq.kms. We will describe the advantages of this method,
some of the challenges imposed by this new way of working and some developments being evaluated.
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Reducing Noise in 3D Seismic Data While Preserving Structural Detail
Authors Saleh Al-Dossary and Yuchun WangWe present a new data adaptive method for smoothing 3D post-stacked seismic attributes. The
method can reduce random noise while preserving the structure without prior computation of the
structure orientation. It works as follows: within a neighborhood sub-window, we smooth the data
along a set of pre-defined orientations; the best result is then selected as output. This best orientation
often approximates to the true structure orientation embedded in the data; therefore, the embedded
structure is preserved. The selection rule for the “best” orientation depends on the data type and
purpose of maneuver; it can be minimum deviation, and maximum, minimum or absolute-maximum
summation. The scheme can be further combined with median, alpha-trim, symmetric near neighbor,
or edge preserving filters. A stop mechanism can be built-in when best orientations cannot be
determined. Our results show that it is an effective way to reduce random noise, eliminate footprint
and to enhance coherence and curvature attributes. It can also be applied to seismic amplitude to
enhance auto-picking of horizons, first arrivals, or refraction events.
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FMI Sedimentological Interpretation, Western Desert, Egypt - An Approach for High Resolution Facies Reservoir Anatomy
Authors Elie G. Haddad and Mohsen Abdel FattahBahariya Formation in Western Desert Egypt is one of the major complex oil bearing reservoirs in
Egypt. Many discoveries have revealed the high oil potentialities of this formation.
Detailed sedimentological interpretation was performed over the imaged highly complicated and
inconsistent reservoir interval for Abu Roash “G” Member and Bahariya Formation in two drilled wells,
North Western Desert of Egypt.
Twenty lithofacies types were defined from the images of the two investigated wells. Individual
lithofacies were defined based on detailed description of sedimentary structures from the image logs.
The sand lithofacies of the Bahariya Formation and dolomite of Abu Roash “G” member were assigned
pay values. The identified electrofacies are calibrated with the cored intervals in one of the two wells.
The Bahariya Formation in the studied two wells is interpreted as a tidal flat deposits and characterized
by the following subenvironment: barrier bars, tidal channel and tidal flat muds. The Abu Roash “G”
member is considered as a subtidal carbonates and characterized by the presence of frequent
secondary dolomite.
Correlation based mainly on the data gained from FMI sedimentological facies analysis and
interpretation has been carried out to through light on the lateral facies changes and consequently to
solve many problems related to the reservoir complexity. The missing of some facies associations
confirms the presence of faulting.
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Improved Understanding of the Athel Silicilyte through the Fara Formation: A Co-Eval Pre-Cambrian Analogue in the Sultanate of Oman
The Athel silicilyte represents a unique type of reservoir in the Sultanate of Oman with only two fields
currently on production in the South Oman Salt basin under pressure depletion schemes. The next
development for one of these fields will incorporate miscible gas injection where sweep efficiency,
injectivity and rapid gas breakthrough are key uncertainties. Since the development of the field, the
lack of an identified depositional analogue has limited the understanding of rock property distribution,
the prediction of facies and potential reservoir extent that all impact these key uncertainties. However,
examination of the Pre-Cambrian Fara Formation in Wadi Bani Awf provides a potential analogue for
sediments with similar lithologies and age of deposition. Characterization of the Fara Formation and the
extent to which it can be directly applied to the subsurface is the focus of our current research.
The screening of the Fara Formation as an analogue has involved detailed measuring of stratigraphic
sections, acquisition of spectral gamma ray, petrography, bulk mineralogy and stable isotope analysis.
Initial results indicate the Fara Formation and the Athel silicilyte were both deposited in an enclosed
basin, starved of clastic input, under reducing conditions and below storm wave base. Both formations
display laminated silicified sediments that indicate seasonality, deposition by traction and suspension
and occurrence of microbial mats. Slumping and fine-grained turbidites are a commonality and reflect
margin instability likely associated to ongoing tectonism. Petrographic and field examinations indicate
dolomite cementation predated silicification and at least two phases of silicification have taken place in
the Fara Formation. This has implications for the silica precipitation model. The large component of
volcaniclastic material in the Fara Formation suggests that volcanic activity and basin configuration
were key factors in the development of the Athel silicilyte during the Late Pre-Cambrian of the
Sultanate of Oman. Unlike the Athel however, the Fara formation also shows a large proportion of
carbonate and a diversity of lithofacies including fore-reef talus deposits, debris flows, turbidites, and
redeposited laminated microbial boundstones that has not been recognized to date in the subsurface.
This paper presents early results and potential implications for exploration and production of the Athel
silicilyte.
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Estimation of Reservoir Properties from Seismic Attributes and Well Log Data Using Artificial Neural Networks
Porosity, permeability are key factors to build a 3D geological model for a reservoir. The best method
to get these properties would be to measure them on core samples in the laboratory. However, this
method is costly and time consuming, and usually only a few out of all wells are cored and even then
only a small portion of the well. To fill the gap in the vertical scale, geologists generally use a statistical
approach, such as linear or non-linear multiple regressions to correlate reservoir properties with the
continuously recorded well log data. Recently, geoscientists have utilized Artificial Intelligence (AI),
especially Neural Networks (ANNs), to predict reservoir properties. This talk reports a comparative
study of two types of neural networks, a Multiple-Layer Perception MLP, with back propagation neural
network, and a General Regression Neural Network GRNN. The viability of these techniques are
demonstrated on well log data and seismic attributes from sand stone reservoir in south of Algeria.
This study utilizes the basic logs including gamma ray GR, interval transit time DT, shale volume VSH,
bulk density RHOB, deep later log LLD and corrected porosity NPHI and five attributes( instantaneous
frequency, instantaneous phase, RMS amplitude, half energy and Arc length) to predict porosity,
permeability and lithofacies in cored and uncored wells. The agreement between the core data and the
predicted values by neural networks demonstrate a successful implementation and validation of the
network’s ability to map a complex non-linear relationship between well logs and permeability and
porosity. Also the results show that the application of the General Regression Neural Network GRNN
gives a relatively better performance than the Multiple-Layer Perception MLP.
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Challenges and Strategies for Near-Surface Modeling for Static Corrections
More LessUnderstanding the geology is vital in modeling the near-surface. The geophysical implications are
rapidly varying vertical and lateral velocities, complete with velocity inversions. Modeling strategies
include elevation correction with sand dune term, and use of refraction statics and tomography. The
modeling challenges include shingling, acquisition geometry, long wavelength and imaging of complex
structures.
Shingling is a near-surface generated en-echelon effect due to shallow inversions, outcropping
refractors, multiple fast thin refractors, or interference. Shingling creates medium and long wavelength
anomalies due to poor definition of the layer velocity field. Strategies for model building include picking
a consistent refractor and averaging all shallow layers as a single weathering layer.
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Memory Cross-Dipole Sonic Tool and Novel Deployment Techniques
Authors Peter J. Williams, Terry Mayor, Dan Long and David EcclesCross-dipole sonic data has broad applications in geophysical, petrophysical and geomechanical
studies. The advent of the small-diameter memory cross-dipole tool improves operational efficiency in
a broad range of well types. The tool combines monopole and cross-dipole acquisition capabilities. It
extends the availability of high-quality cross-dipole data to slim and/or high dogleg wells, and reduces
acquisition risk in high angle wells and wells drilled through formations prone to borehole bridging. In
spite of the tool’s small size and weight, its novel design provides data quality that matches that of
previous generation tools. It is deployed with or without a wireline, and is not constrained by wireline
data transmission rates because data is recorded to internal memory. Deploying the tool inside drill
pipe on the well shuttle facilitates access into highly deviated wells and past bad hole conditions. This
versatility makes cross-dipole data available in a far wider range of wells than has previously been possible.
Operations have been conducted in diverse logging environments around the world, covering a range
of borehole sizes and formation velocities. Comparisons with standard cross-dipole tools have
demonstrated benefits in respect of well access. The data has been used in velocity calibration,
amplitude variation with offset, shear seismic interpretation, anisotropy, Stoneley permeability, rock
strength, and hydraulic fracture design.
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Using Geomechanical and Fluid Flow Models to Predict Hydrocarbon Accumulation Zones
Authors Mykhaylo Dovbnich, Dmytro V. Rudakov and Alexandr BobylovLocation and redistribution of oil and gas deposits resulted by geologically long seepage of liquid and
gaseous hydrocarbons are determined significantly by the stress-deformed state of the Earth in upper
strata of 3-5 km thickness. Lithostatic and tectonic components make a decisive contribution to the
total stress field, with the tectonics effect changing stress essentially. So that accounting for the stress
anomalies of tectonic origin using geomechanical and fluid flow models enables characterizing
reservoirs and determining accumulation zones of hydrocarbons more precise and reliable.
The proposed approach to estimate palaeotectonic stresses within the framework of the elastic medium
theory includes the successive stages: (1) creation of the 3D structure velocity models of sedimentary
deposits using the seismic prospecting data; (2) estimation of boundary conditions to calculate tectonic
stresses by modeling of point displacements on layer boundaries due to long time deformations of the
sedimentary cover; (3) development and identification of 3D geomechanical models based on FEM
algorithms to calculate the tensor of tectonic and lithostatic stresses; (4) hydrodynamic evaluation and
contouring of hydrocarbon accumulation zones.
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Heuristic Model of Hydrocarbon Reservoir Related Microtremors
More LessA number of surveys over different oil and gas fields throughout the world have reported the presence
of spectral anomalies in the passive seismic wavefield (between about 1 Hz and 6 Hz), with a high
degree of correlation to the location of hydrocarbon reservoirs. If these microtremors originate from
the reservoirs, they can be used as a reservoir indicator and for reservoir characterization. A
preliminary model is presented to explain the potential source mechanism of microtremors generating
the spectral anomalies. Poroelastic effects due to wave induced fluid flow and oscillations of different
fluid phases are significant processes in the low-frequency range which can modify the earth’s
omnipresent seismic background spectrum. These processes only occur in partially saturated rocks. We
assume that hydrocarbon reservoirs are partially saturated whereas the surrounding rocks are fully
saturated. Real data observations are in general agreement with this conceptual model.
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Using Spectral Attributes to Detect Seismic Tremor Sources - A Synthetic Study
Authors Marc Lambert, Erik H. Saenger and Stefan M. SchmalholzA method is presented to detect subsurface seismic tremor sources by analyzing surface data. Spectral
attributes of the recorded seismic wave-field at low frequencies are used to map the surface projection
of the sources. We illustrate the concept on a synthetic data-set generated with a homogenous forward
model and show how spectral attributes can be used for detecting locations of seismic tremor sources.
In a second part we apply the method to an example of hydrocarbon reservoir related tremors. The
results show that increased complexity of the subsurface seismic properties and/or the presence of
several tremor sources can strongly complicate the interpretation. In addition, the presence of
dominant surface noise may mask the signals emitted by the subsurface tremor sources and make it
impossible to detect them at the surface without additional processing. F-K filtering is successfully
applied to noise-contaminated data and retrieves masked anomalies. Care has to be taken for using a
proper data-set and proper processing parameters in order to avoid artifacts introduced by the F-K
filter. Although we discuss an application for possible hydrocarbon reservoir related tremors, we
believe that the methods can also be applied to any other type of seismic tremor signal.
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An Advanced Airborne Geophysical Approach for Exploration of Petroleum Resources
By John JosephRecent advances in mapping technologies coupled with the emerging needs of the exploration industry
to precisely characterize the sub-surface systems, have led to the resurgence in interest for gravity
and magnetic methods in oil and natural gas exploration. These methods are typically used in frontier
areas to carry out reconnaissance surveys, to identify new and prospective basins as well as to explore
more seismically challenging areas. An integrated approach combining gravity, magnetics and seismic
along with other geological data is becoming the modern/latest approach for oil and gas explores to
push the envelope and venture into new frontier environments. Traditionally the potential field (Gravity
and magnetic) measurements are time consuming. But the need for acquisition of large gravity and
magnetic data sets at a greater speed has renewed the demands for precise airborne measurement
system, which has unlimited accessibility over any terrain conditions such as coastal areas covering
both land and shallow sea, over remote deserts, marshy lands, thick forests and icy lands etc.
Significance of airborne geophysical approaches have increased with major advances in satellite
positioning technology such as GPS and GLONASS, which enables the determination of 3-D position of
the moving platform (aircraft) with greater accuracy. UTS Geophysics utilizes the latest version of
airborne gravity systems called TAGS (Turnkey Airborne Gravity System) on a fixed wing geophysical
survey aircraft, which is already equipped with a magnetic acquisition system as well as radar and
laser altimeters. Prior to offering the services of this new system, a pre-purchase test of the gravity
meter was undertaken. The system performance was tested mainly in three different ways, (a)
repeatability along predefined survey flight lines, (b) crossover errors and (c) comparison with ground
data. The results provided a high level of confidence in offering this multi-system airborne geophysical
approach to the petroleum industry. A detailed discussion on the system details and test survey results
will be presented.
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Arabian Plate Sequence Stratigraphy: 10 Years On
Authors Michael Simmons, Stephen Cain, David Casey, Roger Davies, Alexis Godet, Peter Sharland and Owen SutcliffeAlmost 10 years have passed since Sharland et al. (2001) published Arabian Plate Sequence
Stratigraphy. This work correlated 63 maximum flooding surfaces across Arabia and, for the first time,
placed the complex lithostratigraphy of the Middle East into a sequence stratigraphic framework. We
will illustrate that:
- Since its publication we have developed the sequence stratigraphic model by further investigations in
the Middle East coupled with an analysis of the validity of the sequence stratigraphic model worldwide.
We now know that with some minor modifications, the Arabian Plate Sequences can be seen globally
and are thus eustatically driven. We have also been able to further develop the model with additional surfaces.
- It is interesting to speculate on the causes this eustasy throughout the Phanerozoic. The pace and
amplitude of the changes points strongly to a glacio-eustatic origin for our sequences this is supported
by a growing body of direct and proxy evidence that points to a coincidence of climatic fluctuation and
eustasy, suggesting that melting and creation of ephemeral polar ice may be a causal mechanism,
even in what is commonly regarded as a “greenhouse” times.
- A robust 3rd order sequence stratigraphic model for the Arabian Plate is a valuable tool for region
correlation and mapping, and the recognition of exploration analogues, as well as placing existing
reservoirs and source rocks in regional context.
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Controls from the Hydrocarbon Entrapment in Burgan and Wara Formations in Kuwait Offshore
Authors Fida Hussain, Riyasat Husain, Abdul Aziz H. Sajer and Ahmad Al-KandaryKuwait Offshore lies to the east of Kuwait with an aerial extent of about 10,000 Km2. It is not
comprehensively explored and only a few wells have been drilled to explore Cretaceous structural
prospects. The objective of the study is to bring out the depositional environments, distribution of
lithofacies and their control on hydrocarbon entrapment for Burgan and Wara Formations.
Burgan Formation of Lower to Middle Albian age is a thick clastic sequence, which is deposited in a
fluvial to marginal marine environment. The formation is broadly divided into two major sand packages
separated by a major shale unit. The lower sand package corresponds to lowstand systems tract while
the upper package corresponds to the highstand systems tract as well as lowstand clastics of the
overlying sequence. In upper Burgan, the fluvial and tidal sands that filled incised valleys are prolific oil
producers in the onshore. Reservoir quality deteriorates in the seaward direction as the valley systems
thin and become mud prone. Wara Formation of Cenomanian age is also a clastic sequence and
comprises of sandstone with interbedded shales deposited in an inner to middle shelf environment. The
formation corresponds to highstand systems tract of the sequence initiated in Upper Burgan. The thin
sandstone beds in Wara Formation are also known commercial producers in onshore.
Prospectivity analysis of the Burgan and Wara formations in Offshore Kuwait has indicated that
hydrocarbon occurrences are controlled by temporal and spatial variations of lithofacies. The study has
indicated that the Kuwait Bay appears to be the most prospective for exploration of these reservoirs in
terms of development of favourable lithofacies associations occurring in favourable structural setting.
High resolution sequence stratigraphy and depositional modeling is key to exploration of these
formations.
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Seismic Source Parameters Optimization in Shallow Water Area Offshore Abu Dhabi, U.A.E
Authors Tomohide Ishiyama, Derrick Painter, Kamel Belaid and Tamer SalehSeismic source parameters are one of the important specifications for a seismic survey. Conventional
thinking is that larger sources produce higher energy, and thereby improve data quality.
In shallow water areas offshore Abu Dhabi, U.A.E, OBC seismic survey is commonly acquired with airgun
array as the primary seismic source. However, the source size is limited due to operational
constraints such as shallow water depth and scattered production facilities. Although several seismic
surveys have been acquired in the region, the impact of source size on data quality is still open for
discussion. In this regards, a 2D-2C OBC pilot seismic survey was acquired in a shallow water area in
the region.
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Simultaneous Acquisition of Near Surface Geophysical Data
By Tom NicolsThis paper seeks to define the problems and solutions developed to enable the simultaneous
deployment and use of multiple geophysics instrumentation from a common platform using the GEEP
technology (Geophysical Exploration Equipment Platform) developed by Geomatrix Earth Science.
For the purposes of this paper the Geophysical boundary is set at the first 100M.
It may be argued that for basic Geophysical exploration tasks such as foundation studies that a single
geophysical tool might suffice. However when addressing more challenging tasks such as
Archaeological research, UXO detection, Karst location, waste location, mineral mapping etc it soon
becomes clear that more than one geophysical tool is not only desirable but is essential to a valid
survey outcome.
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Deepwater West Coast India - Pre-Basalt and Other Mesozoic Petroleum Plays
Authors Glyn Roberts, Charles Harmer, Ken Rutherford and Colin O‘BrienTo date, the main deep (>400m water depth) offshore exploration efforts offshore India has
concentrated on the East Coast where a number of large discoveries have recently been made in the
Krishna Godvari and other basins.
Now attention is turning to the deep offshore area of the West Coast of India where outside the
petroliferous (shallow water) province of the Mumbai High, exploration to date has been frontier in
nature with very few wells drilled.
Using recently re-processed seismic data (from a 12,000 km regional 2D seismic survey collected for
the DGH in 2002) we show how the application of modern seismic techniques (Radon Demultipe, PSTM
and PSDM) has upgraded the petroleum potential of the area - showing plays both in the Tertiary and
in the deeper Mesozoic section where a potential petroleum province can now be recognised below the
Deccan basalts. Our interpretation of this dataset shows that this Mesozoic province extends over
200km offshore and into waterdepths of up to 3500m - covering a large number of open blocks in
Indian territorial waters.
The paper draws on the geology of wells drilled in the Seychelles (and also refers to those in the Kutch
Graben) in order to build up a stratigraphic framework for the Mesozoic off the West Coast of India. It
is illustrated with numerous seismic examples (including data in depth)showing the petroleum potential
of the Mesozoic.
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The Applicability of Gravity Gradiometry as from Exploration Tool in East Dubai, U.A.E
Authors John Alfred P. Protacio, Jonathan Watson, Frank van Kleef and Georgeta PopaThe east of the Emirate of Dubai is dominated by the geologically complex western thrust front of the
northern Omani Mountains. This deformation front is the boundary between the western foredeep basin
and the eastern Omani fold-and-thrust belt.
Complex geology makes conventional exploration challenging. The reservoir (Thamama Group)
structures are thrusted anticlines with the overlying Tertiary units showing large-scale thrusting as well.
The Lower Cretaceous Thamama Group limestone is one of the main hydrocarbon reservoirs in the
Middle East. It forms a major hydrocarbon-producing reservoir in the U.A.E., Iraq, Bahrain and Oman
and has a high hydrocarbon potential in southeast Iraq, offshore Oman and offshore northeast Saudi Arabia.
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Application of C7 Hydrocarbons Technique to Geochemical Evaluation of Asmari and Bangestan Reservoir Oils in Marun Oilfield
Authors Farid Tezheh and Bahram AlizadehThe purpose of this study was to examine the potential of C7 light hydrocarbons as biomarkers for
petroleum exploration to geochemical evaluation of Asmari and Bangestan Reservoir Oils in Marun
oilfield. The Oils from Asmari and Bangestan reservoirs with a variable δ13C‰ ratio -27.10 to -
26.77‰ PDB, and Pristane/Phytane ratio from 0.78 to 0.91 shows the source rock of this oils should
be marine Marl-carbonate. The isomeric parameters of C7 included single-branched and multiplebranched
heptanes and isomeric pairs, such as nC7/Methylcyclohexane ratio vs. Toluene/nC7 ratio, 2-
MH+2, 3-DMP vs. 3-MH+2, 4-DMP, n-Heptane ratio vs. iso-Heptane ratio. The ratios for
nC7/Methylcyclohexane and Toluene/nC7 ranged from 1.5 to 1.8 and 0.53 to 1.23, respectively. The n-
Heptane value and iso-Heptane value ranged from 30.5 to 39.3 and 1.55 to 1.95 respectively and the
iso-alkanes (3RP), cyclopentanes (5RP), cyclohexanes (6RP) ratios ranged from 20 to 47.5%, 10 to
15% and 41 to 70% respectively. The use of this technique as a qualitative tool shows that all the oils
from the Asmari and Bangestan Reservoirs were Super mature, free of biodegradation and generated
from marine Marl-carbonate source.
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Minjur Sandstone Revisited: New Advances in Sequence Stratigraphy and Modeling in the Khashm-Al-Khalta Reference Area (Central Saudi Arabia)
Authors Benoît H. Issautier, Yves-Michel Le Nindre, Abdullah Memesh and Saleh DiniIn connection with the issues of CO2 geological storage in complex reservoirs, the Minjur Sandstone, in
outcrop in Central Saudi Arabia, was selected as a case study for modeling and simulating the spatial
distribution of sand bodies in a fluvial-deltaic system. As a first step, detailed sedimentologic mapping,
sequence stratigraphy and 3D geological modeling were performed in the area of inlet/outlet maximum
activity of the deltaic system.
Compared to the reference studies by Vaslet et al.(1983) and Le Nindre et al., (1987, 1990), the
vertical and lateral variations around the type section were studied in detail, and interpreted with
greater accuracy in terms of depositional features and sequence stratigraphy. This new survey was
specifically designed to collect 3D information for numerical modeling.
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3D Localized Prestack Depth Migration from Workstations
Authors Xiaomin Zhao, Jianming Sheng, Ying Hu and Chengbin PengWe have recently developed a localized prestack depth migration workflow based on proprietary
technology that is equivalent to Gaussian Beam migration. This workflow enables the 3D prestack
seismic depth imaging of a target volume within a few hours or even minutes. The work flow can be
performed on a single workstation or a cluster of compute nodes, and the quality of the results is very
good, consistently better than Kirchhoff, WEM, and beam migrations. In contrast to conventional
workflows that typically require weeks or even months for an updated prestack seismic depth
migration volume to be produced, the new toolkit provides a near real-time solution to prestack depth
imaging. The migration works for both isotropic and anisotropic velocity models (VTI and TTI), and
handles data acquired with narrow or wide azimuth acquisition geometries. Real data examples are
presented here to demonstrate the new workflow.
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Accurate Conversion between Offset Image Gathers and Angle Image Gathers
Authors Jianming Sheng and Chengbin PengMost migration methods produce either common-offset-gathers (COG) or common-angle-gathers
(CAG) gathers. But none produce both, that is until now. We have developed an accurate and efficient
method that converts common offset image gathers to common angle image gathers, or vice versa.
The practical uses of the method are for velocity analysis or AVO studies using existing commercial
toolkits.
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Non-Hyperbolic Reflection Tomography for Better Imaging and Interpretation
Authors Zhaobo Meng and Chengbin PengIn this abstract we will demonstrate that the application of non-hyperbolic reflection tomography can
produce a 3D subsurface velocity model that is smooth for prestack depth migration and at the same
time geological for accurate subsurface pore pressure prediction and lithology interpretation. Our nonhyperbolic
reflection tomography workflow is very different from the conventional reflection
tomography workflow: no automatic volume picking of residual moveout is used. Instead a set of
prestack events are interpreted on prestack seismic image volumes. The prestack events carry detailed
moveout information that is more accurate than a single parameter fit to the common image gathers.
In addition the prestack events carry structure dip information that is needed for accurate 3D ray
tracing offset by offset. Examples will be given for both compaction driven and lithology controlled
geological environments.
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Gaussian Beam De-Migration and Re-Migration
Authors Jianming Sheng and Chengbin PengIn this abstract we will present a theoretical framework for demigration of seismic image data under
the frame work of Gaussian Beam theory. The underlying methodology has no dip limitation and
handles multi-valued arrivals well. The practical use of this technology is to perform prestack
demigration of existing image volumes (CIG gathers) followed by prestack depth remigration using a
replacement velocity and/or anisotropy model. The result is a fast, accurate, and cost effective way to
improved seismic imaging as compared to proprietary reprocessing from field tapes.
Ross Hill published seminal works in common offset Gaussian Beam prestack depth migration (Hill,
1991 and 2001). Chevron has been largely the only beneficiary of the Gaussian beam technology. To
the best of our knowledge there have been no published work on Gaussian beam prestack demigration.
For example, in prestack demigration, one can start with an individual common offset image volume
(Kirchhoff migration volume, Gaussian beam migration volume, or fast beam migration volume). The
single fold image is demigrated to reconstruct the corresponding input unmigrated seismic data. In
Gaussian Beam prestack demigration, we actually reconstruct the individual beams used as input to
the original Gaussian Beam migration. The individual beams are then synthesized to form an
unmigrated seismic volume.
There are many uses of Gausian Beam prestack demigration technology. For example, it can be used
as a fast forward modeling tool to generate synthetic data for migration and inversion. Another use of
this technology is to perform prestack demigration of existing image data, followed by prestack depth
(re)migration with a replacement velocity and/or anisotropy model. This is a faster, more accurate and
cost effective way of seismic imaging over proprietary reprocessing from field tapes. Both synthetic
and field data examples of this will be shown.
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Plays and Prospectivity Offshore Lebanon, Syria and Cyprus: New Insights from Depth Imaged Seismic Data
Authors Glyn Roberts, Charles Harmer and Dave PeaceThis paper illustrates the nature of the Levantine Basin and adjacent areas based on an analysis of
modern seismic data. It shows that the Basin is comprised of a substantial thickness (> 10,000
metres) of Mesozoic to Cenozoic sediments above a rifted terrain of probably Triassic- Lower Jurassic age.
Depth imaged sections are used to show the nature of the Basin including its relationship to the
Eratosthenes Seamount and the Larnaca Thrust Zone.
Depth imaged sections (with Time Migration comparisons) are also used to illustrate some of the
numerous plays seen in the area. These consist of:
1)Jurassic and older: faulted structures, rollovers and basin margin plays.
2)Upper Jurassic to Middle Cretaceous: mounds, reefs, progrades, drape structures,
structural/stratigraphic plays and unconformity plays.
3)Middle Cretaceous to Paleogene: anticlines, fault blocks, rollovers, mounds, drapes,
structural/stratigraphic plays and basin margin pinch-outs.
4)Sub-Salt (with salt as the seal) and Intra-Salt (Messinian): pinchouts, bright spots, channels and mounds.
5)Post Salt (Pliocene to Recent): channels and mounds.
Depth imaging of the seismic data is shown to aid the evaluation of many of these plays and to
highlight the prospectivity of offshore Lebanon, Syria and Cyprus.
Reference will also be made to both the ongoing and future bid rounds; and to some of the issues
involved in producing velocity models for Pre Stack Depth Migration including the subsequent time
conversion of depth migrated data.
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Undepleted Pockets of Gas Detected Using Coupled Modeling of Subsidence and Reservoir Depletion Processes
More LessAn important cause of subsidence is the withdrawal of large volumes of natural gas, oil and water from
hydrocarbon reservoirs. Every point of depletion in the subsurface causes a subsidence bowl with a
radius corresponding to the depth of the depletion point. The depletion of a large volume in the
subsurface leads to a subsidence bowl of which the shape and the size are directly related to the
subsurface properties and processes. Besides the amount of hydrocarbons produced and the geometry
of the reservoir, relevant features include the subsurface elasticity profile, the compaction coefficient
and the strength of the aquifer.
Surface subsidence measurements (e.g. Interferometric Synthetic Aperture Radar (InSAR), leveling
measurements, or GPS) can be used to better quantify the subsurface parameters and processes.
Simple inversion approaches do not usually provide a sensible solution due to non-uniqueness of the
solution and the sensitivity of the inverse problem to small fluctuations in the data. We have developed
a time-integrated inversion scheme for resolving the spatial and temporal reservoir pressure drop from
surface subsidence observations. This inversion procedure is unique because it utilizes all the available
prior knowledge including the uncertainty and the correlations within it. Elements of this prior
knowledge are the geological model, the reservoir model, the sealing properties of faults, and the acquifer activity.
We have applied our inversion method to a highly compartmentalized reservoir in the Netherlands
where we used the observed surface subsidence (leveling), the geological model, the reservoir model,
and the prior knowledge about possibly sealing faults, to obtain insight into undepleted pockets of
natural gas in the reservoir. We used prior models which complied with the measured flux and pressure
measurements of the production profile. With these data, we were able to better quantify the amount
of compaction in the different compartments in the reservoir and the pressure depletion causing it.
The approach followed is essentially a two-step approach: the history match is the first step, and the
inversion of subsidence measurement the second. The risk of this approach is that not the complete
solution space is being searched. We are currently also developing an approach in which the inversion
of production data and subsidence measurements are integrated.
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The Levantine Basin - Prospectivity in a Frontier Basin
Authors Thore Sortemos, Caroline J. Lowrey, Cecilie Skiple and Mark TrayfootThe prolific Nile Delta to the south is an active petroleum province, but exploration activity in the deep
water Levantine Basin offshore Cyprus, Israel and Lebanon has been limited. However, the recent deep
water subsalt gas discoveries offshore Israel, the announced 2nd licensing round offshore Cyprus in
2009 and the planned 1st licensing round offshore Lebanon has spurred a significant increase in
industry interest in the area.
The Levantine Basin is bound to the east by the Levantine margin, to the north by the Latakia Ridge
and to the west by the Erastosthenes Seamount and is interpreted as a Mesozoic transform rift graben.
Our interpretation and the Tamar discovery indicate that much of the pre-Messinian sedimentary
package in the Levantine probably consists of Oligocene to Miocene successions, rather than the Early
Cretaceous/Senonian successions suggested previously.
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Komombo: A New Oil Province in Upper Egypt
Authors Mohamed Fathy, Leonardo Salvadori, Glyn Roberts and Moussa Abu GoudaThe paper discusses some of the geological and geophysical work performed in Centurion’s Block 2
concession area in Upper Egypt; and which lead to the discovery of the Al Baraka field in 2007 -
leading to the opening up of a new petroleum province in the Mesozoic rift basins of Upper Egypt.
The Komombo Block-2 Concession is located on the west bank of the Nile River, about 570 km SSE of
Cairo, and about 260 km east of the Red Sea. It was part of a larger former Repsol concession which
was relinquished in 2001 after the drilling of five wells.
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Reservoir Connectivity and Fluid Uncertainty Analysis Using Fast Geostatistical Seismic Inversion
Authors Ashley M. Francis and Graham HicksStochastic seismic inversion (Haas and Dubrule, 1994; Francis, 2006) enables the uncertainty in
seismic inversion to be explored. Additional information in the well logs is statistically exploited in
accordance with the variogram model. Each stochastic seismic inversion realisation has a spatial
constraint imposed by a variogram, is conditional to the well and stratigraphic horizon data and is
conditional to the seismic data within the bandwidth of the wavelet. Using a frequency domain fast
stochastic seismic inversion algorithm a sufficiently large number of stochastic realisations enables
probability and 3D connectivity volumes corresponding to lithology or fluid indicators to be generated.
Two applications of 3D Connectivity analysis of stochastic seismic inversion realisations are presented.
In the first example using post-stack seismic inversion impedance realisations, the acoustic impedance
is classified by sand and shale discriminators (Francis, 1997). The sand indicator is used to process
each realisation using 3D connectivity to identify geobodies. By selecting realisations containing
geobodies which are consistent with known connectivity criteria between wells, these realisations can
be used as candidates for constraining geostatistical modelling.
In the second example, pre-stack seismic inversion results and a rock physics analysis are used to
identify hydrocarbon fluid effects from the seismic response. Pre-stack inversion using Extended Elastic
Impedance (Whitcombe et al, 2002) is used to generate a large number of joint stochastic impedance
realisation pairs. Based on the rock physics analysis the EEI impedance realisation pairs are rotated to
obtain pairs of optimal fluid and lithology predictor realisations. The rotated realisation pairs are used
to evaluate the probability of new well targets being partially depleted by existing production, to
estimate sand volumetric uncertainty and to perform a risk analysis of a proposed horizontal well trajectory.
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Processing Methods for Extracting Subsurface Information from Ambient Seismic Noise
Authors Barbara Schechinger, Alexander V. Goertz and Marc LambertThe ambient seismic wave field carries information about the subsurface in the vicinity of the recording
site. It also carries a lot of less useful information about anthropogenic activities nearby. Potentially
interesting variations in the naturally occurring seismic background wave field happen at extremely low
power spectral density levels (typically between -120 to -180 dB [w.r.t. 1 m/s]), and is oftentimes
masked by noise of anthropogenic origin. In addition, the spatial, temporal and frequency-domain
variability of cultural noise often exceeds the variations of the natural background wave field. It is
therefore critical to remove any influence of cultural noise from the records before an attempt can be
made at analyzing the ambient seismic noise level with respect to any meaningful signatures of
subsurface variations. Here, we present methods to characterize the ambient seismic wave field
recorded with broadband seismometers and propose methods for extracting subsurface-related
information. The analysis includes the characterization of spectral signatures of different types of
sources (both anthropogenic and natural origin), as well as spectral signatures that are indicative of
the subsurface underneath the recording site. The characterization also drives the selection of certain
noise-removal techniques. Due to the typically small amplitude of these subsurface-related variations,
it is critical to remove as much of the surface energy as possible, and to correct for near surface effects
in the recorded data. Analysis of the cleaned data then allows looking for special attributes that may
carry subsurface information. A possibly important tool for achieving these goals is the ratio between
vertical and horizontal components (V/H) in the frequency domain. In this domain, the receiver terms
contain information about the shallow subsurface, but sometimes also information about fluid content
in the deeper subsurface. Both pieces of information can be of use in practical applications. For
illustration, we present examples from low-frequency passive seismic (LFPS) surveys with particularly
strong anthropogenic noise contaminations. We show that, despite remnant contamination of the
records by anthropogenic noise, we observe statistically significant variations of spectral attributes that
can be used for subsurface characterization.
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Seismic Repeatability - Is There a Limit?
The results of a 13-day seismic monitoring experiment are presented. It consists in 2 permanent
piezoelectric sources, one cemented in depth and the other attached to a surface concrete pad and 28
sensors, 14 at the surface and 14 cemented below the weathering zone.
To enhance the signal-to-noise ratio, continuous averaging of the individual SP records is performed
providing an average daily SP. 4D attributes are measured on these daily averages. The best
repeatability is obtained when both sources and sensors are buried with time and amplitude variations
of 6 μs and 0.5% respectively. This extremely high precision level is far above what can be expected
from the most accurate surface acquisition methods currently available.
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Reservoir Facies and Sequence Stratigraphy of the Khasib Formation in Selected Fields from Central Iraq
More LessThe bioturbated chalky limestones of the Khasib Formation (Upper Turonian - Lower Coniacian) furnish
an extensive reservoir rock of several oil fields in central Iraq including: Tikrit, Balad, Samarah, and
East Baghdad oil fields. Investigation of these rocks by means of microfacies analysis and electrofacies
correlation as well as sequence stratigraphic analysis indicate that it had being deposited in a ramp
setting sloping east- southeastwards forming part of the Arabian passive margin.
The inner ramp is characterized by a bioclastic packstone of a carbonate bank with green shale
intercalations of peri-bank sediments. The middle ramp which dominate the Khasib Formation section
is consist of white- beige, porous, bioturbated, chalky and dolomitic bioclastic wackestone. Bioclasts
includes; shelf faunal debris with variable mixture of benthic and planktonic forams. Intensive
Thalasionodes and Palaeophycus bioturbations significantly contributed to the high porosity of this part.
The outer ramp is consists of intercalations of boiturbated bioclastic chalky limestone and basinal
argillaceous limestone. The latter is characterized by the occurrence of planctonic forams, calcispheres,
dwarf rotalids and sponge spicules.
The Khasib section represents a third order cycle with lower sequence boundary of type one separating
Khasib sequence from the underlaying LST of the Kifl Formation. The TST is consist of thin and basinal
facies. The HST is the thickest and represented by the bioturbated chalky limestone of the middle ramp
facies. The maximum flooding surface is idicated by a thin horizon dominated by intensive Paleophycus
bioturbation within the middle ramp facies. The boundary with the overlaying Tanuma Formation is of
type two and represented by the transition to the LST of the next cycle.
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