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GEO 2010
- Conference date: 07 Mar 2010 - 10 Mar 2010
- Location: Manama, Bahrain
- Published: 07 March 2010
61 - 80 of 457 results
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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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