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3rd EAGE North African/Mediterranean Petroleum and Geosciences Conference and Exhibition
- Conference date: 26 Feb 2007 - 28 Feb 2007
- Location: Tripoli, Libya
- ISBN: 978-90-73781-42-9
- Published: 26 February 2007
61 - 80 of 100 results
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Determining Reservoir Connectivity in Producing Fields – Examples from Eastern Canada and the Gulf of Mexico
Authors M.L. Sweet, P. Vrolijk, L.T. Sumpter, J.W. Snedden, R. Myers, B. James, E. Meurer and A. MosolaMaximizing recovery from oil and gas fields requires an understanding of the initial distribution of fluid contacts that may vary between segments of the field. It also requires an understanding of which geologic elements affect connections between wells as the field is produced. We have developed a technique, Reservoir Connectivity Analysis (RCA), for rigorously defining differences in fluid contact elevation and relating these contact differences to geologic elements with the goal of identifying pre-production, reservoir compartments. This technique has been applied to more than a dozen ExxonMobil fields in depositional environments ranging from aeolian to deepwater and in structures that range from simple folds to complexly folded and faulted structures. Some of these studies have led to successful predictions of contacts in previously undrilled compartments of mature fields. In other cases, we have found that as the field is produced these geologic features affect production by limiting drainage area and pressure support. In addition to geologic features that control contact elevation over geologic timescales, we have observed other features that may be transmissible over geologic time, but that affect connectivity as the field is produced.
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3D Seismic Data Attribute Analysis for Predicting Wara Reservoir Qualities in the Al-Khafji Field, Middle East
Authors K. Chakraborty, S.L Nimmagadda and M. Al-HajeriReservoir property such as porosity, its lateral variations and areal extensions can be predicted from seismic attribute data, if they are appropriately calibrated and integrated by vertical seismic profiling (VSP) and petrophysical data. Objectives of the present study are to explore Wara reservoir qualities and their spatial distribution and examine its stratigraphic trapping mechanism by 3D seismic imaging. Gross porosities and sand volumes have been computed and mapped at well locations and seismic crossings. Seismic attributes calibrated at well locations, have been mapped all along and across the seismic grid covering the entire Al-Khafji field area. Cross plotting between seismic attribute values and well driven-porosities has facilitated to derive a correlation function and estimate of porosity attributes. Porosity estimation using seismic attributes of their seismic locations provide good confidence and its confidence is better improved at well locations thus describing reservoir properties between wells and away from wells. Porosity maps derived from well-data combined with calibrated seismic amplitudes and computed sand volume maps, predict sand bodies and their lateral extensions, particularly in the eastern part of Al-Khafji oil field, which open up additional exploration areas for Wara reserve accretion in the Gulf of Kuwait.
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Constraining Reservoir Models by their Diagenetic Overprints - Impact on Reservoir Connectivity
Authors R. Labourdette, A. Meyer, M. Sudrie, F. Walgenwitz and C. JavauxDolomitic formations constitute one of the most important reservoirs in the Middle East Region. The complex diagenetic history which prevails in these reservoirs impacts on the final static and dynamic reservoir properties. Therefore in order to optimise the current production of reservoirs and future field development plans, it is mandatory to: •understand the type, impact and timing of the main diagenetic phases at all scales from regional understanding to the fine-scale reservoir heterogeneities in order to constrain geometry, •and develop approaches to effectively incorporate the most significant ones into the static reservoir model. Dolomitization is one of the most crucial diagenetic phases since it strongly constrains the permeability architecture of the field. Detailed diagenetic studies suggest that various types of genetic dolomite types exist, including evaporative, mixed evolved sea-water - freshwater and late thermobaric dolomites. The modelling approach is geologically-driven and based on the relationships between dolomite type, stratigraphic position, palaeogeographic position, depositional facies, and proximity to fault/fracture zones. The results are then quality controlled to ensure coherency with the conceptual models. The outcome of this modelling workflow is fed into a dynamic simulator to assess the potential impact on field behaviour, production profiles and well productivities.
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Geologic Modeling and History Matching of Production Fields Using an Integrated Geologic/Engineering Approach (RETR)
Authors L.H. Landis, B.A. Proett, J.J. Lawrence and C.J. LyttleThe Reservoir Evaluation Time Reduction (RETR) methodology was developed to improve the process of building reservoir simulation models and reduce the time required to establish the technical basis for business decisions. This integrated history matching process was tested on four producing fields of varying stratigraphic complexity, number of wells, and depositional environment. These tests demonstrated that using the RETR process offers several advantages over the traditional approach.
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Optimal Reservoir Management and Field Rejuvenation – Key Geoscience Technologies and Trends
By K. RudolphThe objective of this discussion is to provide a broad overview of Integrated Reservoir Management, using examples from fields around the world. Reservoir management can be viewed as a three component learning system. The first component is reservoir characterization based on the analysis and interpretation of fundamental geoscience and engineering data. The second is quantification of the subsurface via a geologic model, reservoir simulation, and facility model, providing the basis for future depletion plans. The third stage of learning follows production start up as we collect production surveillance data to evaluate the accuracy of the geologic interpretation and development plan. This repeated cycle of interpretation, modeling, and production feedback drives continuous improvement of the subsurface model and depletion plan, maximizing value from both new and mature fields, and cost-effectively recovering more oil and gas
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Qualitative Characterization of Silurian
Authors R. Perona, J. Dessay, J.L. Algibez, J.M. Gonzalez Muñoz, M. Sweed and J.J. MartinIn most prospects drilled the Upper Ordovician Mamuniyat formation is the main target, being the Tanezzuft formation the covering seal of the petroleum system. In this case a prompt identification from Mudlogging data of its basal member (“Hot Shale”) would be helpful for: - Correlation while drilling. - Anticipate the top of possible reservoir for opearional purposes.
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A New Workflow for Better 4D Seismic Interpretation
More Less4D seismic images are often replete with artifacts of the time-lapse methodology, unrelated to actual changes in properties within the reservoir. These artifacts introduce uncertainty into the interpretation of flow fronts and pressurization and can greatly diminish the value of the 4D data. In many cases the artifacts originate from seismic signal and noise which cannot be, but, ideally should be exactly repeated from one survey to the next. Practical limitations of seismic acquisition and processing technology inherently limit data repeatability. Current 4D workflows rely heavily upon seismic repeatability. Current workflows utilize subtraction of data (or images) from repeated surveys to localize changes in properties to the time interval between surveys. These subtraction-based methodologies therefore assume that repeated signal and noise will subtract to zero provided subsurface properties have not changed over time. One can relax repeatability requirements by direct inversion for the changes in properties between two surveys. This new 4D workflow avoids subtraction altogether and can greatly reduce artifacts and uncertainty in the resulting images. Improvement is particularly evident for time-lapse relative to the pre-production conditions of the reservoir. These pre-production properties have frequently been recorded through a legacy seismic survey with particularly poor repeatability.
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Contributions of the Seismic 3D in the Interpretation and Comprehension of Geometry of the Paleovallees of the Ordovician
By S.S. SaibMany studies treat of deposits and processes of Ordovician paléovallées within the Illizi basin. Their limits and their extensions remain difficult to understind. These deposits are characterized by a short and glacial episode, which are responsible on the formation of irregular incisions in Ordovician. This results in depressions filled by the deposits of the various units of the upper Ordovician (IV-3/IV2/IV-1). They can reach 300m depths and rest on the various units under unclaimed of Ordovician, or on Cambrian unit II, even directly on the Précambrien base. Their widths are variable 1 with 3Km. Two types of orientations have summers met NW SE and WNW - ESE in the Illizi basin. The acquisition of 3D seismic in the study area, not only makes it possible to include/understand their geometry, their orientation but also to delimit them with precision. The seismic interpretations, combined with the geological data (ground, well, cores etc....) allow to have another design of these paléovalées, as well as the oil potential which is associated.
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Imaging Vertical Boundaries Using Duplex Wave Migration
By B.H. LinkConventional 3D anisotropic prestack depth migration provides accurate structural boundary information for events with dips from 0 to about 70 degrees. For vertical or near vertical events conventional methods rely on turning wave technology that will only be accurate if the recording aperture is very large and the depth model is known to a very high degree of accuracy. Also, the energy to perform this imaging methodology will only be recorded if the velocity depth model is characterized by significant vertical velocity heterogeneity. Duplex Wave Migration is a newly developed technology that is capable of imaging only vertical events (plus or minus 20 degrees) and it does not require either a large recording aperture or any specific a velocity model that must have strong vertical velocity heterogeneity. It is planned that this paper will provide the first examples of the use of this technology on North African data.
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Palaeozoic Sequence Development and Stacking Patterns - A Tale of Moving Continents and Changing Climates
Authors P. Spaak, D. Middleton and S. MurfittSeveral prolific Palaeozoic petroleum systems are present in North Africa and the Middle East. The stacking patterns and trends of the Palaeozoic hydrocarbon-bearing successions of this vast area show trends and similarities that can be contributed to climatic and tectonic events. Several of these events and their impact on the sedimentary record will be discussed.
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Review of Recent Satellite Image Analyses of the Ghadames Basin (Libya) and the Tassili Region of S Algeria
Authors R.N. Diggens and J.N. DiggensThe Ghadames Basin is a prolific hydrocarbon province with a complex and long petroleum geology history. An integrated approach to understanding its regional structure is essential for exploration success in the region. The remote sensing analysis of Earth Observation (EO) data for the surface expression of sub surface structures is a very cost-effective method for a refinement of the interpretation of sub-surface data for the geometry, interaction, timing and distribution of structures, lithologies and sedimentary features. This study is based on new work carried out on several different types of satellite imagery at different resolutions. A major analysis of the EO data was also undertaken in order to better understand the Late Ordovician glaciogenic deposits in the region with a view to using them as direct analogues to assist in the interpretation of the equivalent horizons in the subsurface data. The Late Ordovician sediments appear to be a channelised, reworked, sheet complex containing associated sedimentary features, which are consistent with having been deposited in a fluvial to marine regime coeval within a glaciation environment. The outcrops show evidence for multiple phases of glaciation, with older sediments being eroded and reworked by subsequent glacial forces.
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Hydrodynamism Implication in Exploration: Triassic Sandstones Reservoirs (Tagi Fm.)in Southern Tunisia
By A. MaazaouiThe main purpose of this technique was to help understand the complex flow patterns synthesis of Triassic sandstones reservoirs, main hydrocarbon producer in Southern Tunisia. Compilation and mapping of chemical analysis of available formation water, static pressure, total dissolved solids with possible classification and potential level distribution at top TAGI formation was accomplished. The obtained results provide the basic information to understanding the relationship between recharge and discharge zones, origin and causes of variation in chemical composition and genetic water types of these subsurface waters. Therefore for better assessment of possible and additional hydrocarbon accumulation It was essential to integrate the above results with facies distribution, tectonic events, fluids attributes and their hydrodynamic effects on entrapments and highlight the most likely trends of additional hydrocarbon accumulation (exploration leads). This study can assist moreover to understand and to may explain why we have inefficiently drilled wells, by using fluids migration paths in respect to hydrocarbon draining area and perhaps to allow outlining the remaining prospective plays for accurate drilling. In other hand, this method may increase the successful ratio of drilling if we have regular and sufficient chemical formation water analyses.
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Maturity Modelling and Hydrocarbon Charge In South-Western Berkine Basin, Eastern Algeria
Authors M. Arab and R. SoulaliThe South-western Berkine basin is a depression bordered by two structural trends (Rhoure- Nouss and Gassi- Touil- Nezla) associated to important gas and oil fields whose Triassic and upper Silurian reservoirs are sourced from Silurian hot shale. These radioactive shales, at the base of the Silurian formation, are dated Llandovery. They are 10-60m thick in the structural zones and up to 80m in the Marfeg trough. The organic matter is marine type II. The organic richness is fair to good, the TOC values range from 2 to 8%. The maturity level decreased from the Marfeg trough (dry gas window) to the flanks (Rhourde-Nouss- Hassi-Touareg) (oil window).
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Trap and Petroleum Models of Gara Gara South Fields Illizi Basin South East Sahara, Algeria
By M.D. MebbaniThe Illizi basin is one of the most potential and mature basins in Algeria where many oil and gas were discovered since 1950s. Among these, Gara Gara South Fields located in the center of Illizi basin. Several oil and gas accumulations of various sizes have been found within the F6 reservoir of Silurian-Lower Devonian age and Ordovician in the Illizi basin. Lithologically, the F6 reservoir consists of interbedded sandstones and shales and is subdivided into M, A, B and C units. These reservoirs, which were deposited in offshore coastal bars and tidal channels, show a high degree of lateral and vertical facies variation. The Ordovician reservoir is known by the rapid variation of facies due to the glacial environnement. There are units which produce in some area but does not exist in others. This paper describes the petroleum geology of F6, which contains a gas cap and a rim of oil, and Ordovician reservoirs. In this area, Ordovician does not produce. Also, the purpose of this study is to determine the trap and petroleum models of Gara Gara South Fields, to compare the 2D and 3D interpretations and to explain the wells results.
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Production Optimization of Gas Wells - Problem of Water Influx
By M. BoussaThe field of Hassi R' mel is a gas condensate reservoir with a superposition of three layers A - B - C having very good petrophysic characteristics and a rather significant oil rim in the Eastern and Southern peripheries. Producing wells were drilled in
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Evolution of Glaciogenic Stratigraphic Interpretation with Improved Seismic Data in Tiguentourine Field, Algeria
Authors A.R. Hutchison, D.E. Sawyer, S.R. Tod, B. Taylor, D. Buddery, I. Alstadsaeter and D. AbdelouafiThe application of modern full azimuth seismic technology in the Cambro-Ordovician of the Tiguentourine Field, Algeria, has allowed stratigraphic interpretation of the sub-surface at an unusual level of detail. Careful use of analogues has given a high level of confidence in tunnel valley interpretations. Sub-division of the reservoir has also improved very significantly, backed up by improving well to seismic ties. The tool will be extremely valuable in well planning, understanding reservoir surveillance data, and in reservoir modelling. Principal contacts regarding this project are D.Buddery (BP; acquisition), B.Taylor (BP; instigator of the project, planning, processing).
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FMI Characterisation of Late Ordovician Facies & Surfaces (Murzuq Basin)
Authors J. Joubert, J. Moreau, J.L. Ghienne and J.B. RosThe imager analysis is justified by a sedimentological purpose - a detailed evaluation of the reservoir intervals to include sedimentary feature analysis, manual dip picking and small-scale structural features.
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Rock Physics Analysis of an Anisotropic Tight Gas Reservoir - A Field Case
Authors P.O. Lys and J. MarrauldIn this paper, we present the methodology we used to build a Rock Physics Model adapted to fractured Tight Gas Reservoirs. Azimuthal anisotropy is modelled in order to evaluate a 3D azimuthal seismic added value.
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Optimizing Production Gas Wells by Using a Dual Completion Hassi R’mel Field, Algeria
More LessDual completion was for a long time used to produce wells perforated on several zones. This type of completion concerns especially the oil wells, but few or not used on the gas wells. In order to improve the production in the upper zone of gas wells, a study was carried out on production gas wells with 2 layers and 3 layers in Hassi-Rmel's field. This field is located 500 km southward from Algiers in the Algerian Sahara and is one of the largest wet gas reservoirs in the world. The gas-producing Hassi R’Mel field has three distinct reservoir horizons, zones A,B and C. The zone A sandstones are composed of very fine grained sandstones which are locally clay-rich with anhydritic cementing in some places. The zones B and C have very good reservoir quality with permeabilities to gas ranging from 300 to 1200 mD. Zone A also has very good reservoir quality for gas , however, it has lower permeability of generally less than 300 mD. PLT recorded on these wells showed that the lower Zones B and C contribute to the majority of the gas production with the upper Zone A providing a lower contribution to the total production, in spite of an acidification of this layer. The isolated zone C of some wells due to the water influx generated an increase in the flow of zone A. This result pushes us to take in consideration the completion and to suggest to carry out a dual completion for the producing wells with several zones in order to improve the production of the zone A which is obstructed by the good potential of the zone C. This study will make it possible to show the necessity to use a dual completion on the producing gas wells with several layers, in order to improve the production of the upper zone and for avoiding having a cross-flow from this one towards the lower depleted zone. The results carried us made it possible to make a technical and economic study which will enable to see the impacts on the reservoir, on the well's equipment and investment costs. The purpose of this presentation is to show: -the advantages and disadvantages from this completion on gas wells. -the ratio of the profit on the capital costs after these completion.
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Survey Performances of the Polymers in the Water Based Systems Used to Drill Deep Wells
More LessA laboratory study has been undertaken to elucidate the influence of structural parameters of polymer/electrolyte systems commonly used for the formulation of water-based drilling fluids on their performances as filtrate reducers or viscosifiers.High temperatures and salt conditions encountered in the well may modify the rheological properties and this makes the use of polymers necessary. High molecular weight polymers (XC, gums, polyacrylamides), have been used in the formulation of water-based drilling fluids for reducing filtration, facilitating clay stabilisation, improving débris suspension capacity and drillstring lubrication in the drilling operation. The rheological behaviour has been modelised. The modele describe structural changes under shear or at rest as well as the associated stress growth makes it an attractive tool to use in order to improuve hydraulic predictions in deep well drilling.
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