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GEO 2008
- Conference date: 03 Mar 2008 - 05 Mar 2008
- Location: Manama, Bahrain
- Published: 03 January 2008
361 - 380 of 385 results
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Evaluation of the hydrocarbon potential of the Upper Jurassic Barserin Formation using biomarkers, Kirkuk and Taq Taq oil fields, northern Iraq
Authors Dler Hussain Baban and Shadan Mahmood AhmedThe source rocks from the Jurassic Barserine Formation were studied from two wells in Kirkuk and Taq Taq oil fields in northern Iraq. The GC, saturate GC/MS, and saturate and aromatic carbon isotopes (δ13 C) of 12 extracts and two oil samples were evaluated for oil-source rock and oil-oil correlations. The GC, biomarkers and isotope data of the extracts and oil indicate and they were all derived from marine carbonate source rocks, composed of predominantly algal-bacterial organic matter deposited under anoxic condition. Very minor variations in biomarkers characteristics are present among the extracts and between the extracts and oils, which may be due by minor variations in organic facies and depositional condition (relative anoxicity) within the Jurassic source rock unit. The sterane maturity ratios suggest both the rocks and oils have comparable maturities and are moderately mature; the Taq Taq oil is exceptional having a slightly higher maturity. The estimated maturation of the Tertiary Kirkuk oil and the extracts are within the 0.70–0.80% Ro range. The maturity of the oil from the Cretaceous of Taq Taq could be about 0.85–0.90% Ro. The somewhat higher maturity of the Taq Taq oil is also shown by the GC data (Pristane/n C17 versus Phytane/n C18 relationship).
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Enhancing the low-frequency content of vibroseis acquisitions with maximum displacement sweeps: A case history from Kuwait
Authors Claudio Bagaini and Adel El-Emam and Ayman ShabrawiSeveral applications of the seismic method to hydrocarbon exploration and reservoir characterization would greatly benefit from the presence of energetic low frequencies in the acquired data. Some of these applications are deep imaging, imaging beneath high-velocity and highly absorbing formations, inversion of surface waves to characterize the near-surface elastic properties, velocity model estimation in geophysically complex areas and acoustic impedance inversion. Unfortunately, the generation and the accurate recording of low frequencies was and, to some extent, remains challenging in both marine and land seismic. In the case of land seismic acquisition, the growing use of accelerometers in surface and borehole seismic enables the acquisition, with an high signal-to-noise ratio of frequencies lower than 2 Hertz. On the source side, hydraulic vibrators, which are the most widely used onshore seismic sources, have their output energy limited at low frequencies by mechanical constraints such as the maximum reaction-mass displacement. Only low actuator forces can be used to drive the vibrators at these low frequencies, which in turn can yield extremely long sweeps in the absence of a design criterion or if a too-conservative one is used. In this presentation, we first analyse the reasons why the above-mentioned seismic applications do benefit from the presence of energetic low frequencies. We then focus on two of these applications, namely: (1) imaging beneath high-velocity formations, and (2) acoustic impedance inversion. We show the enhancements obtained during a recent point-receiver surface seismic survey over the Minagish field in Kuwait acquired using a sweep design method (maximum displacement sweep) developed to enhance the low-frequency content of land seismic acquisition.
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Reducing uncertainty in water saturation in carbonate reservoirs of southern Iran: A regional correlation for cementation factor
More LessThe calculated value of water saturation (Sw) in a field is based on petrophysical parameters combined with a saturation equation. The exactness of calculated water saturation values depends on accuracy of the input parameters. Monte Carlo modeling of water saturation in different wells in southern Iran revealed that the cementation exponent (m) is one of the most important parameters dominating uncertainties in calculated Sw. The cementation exponent is normally measured in laboratory from core experiments. Alternatively it can be estimated from resistivity and porosity logs in the clean water-saturated intervals using Archie’s equation and Pickett plot methods. Applying a constant value for m using above methods resulted in very high uncertainty in calculated water saturation (negative median in oil zones and higher than 100% in water zones). This abnormality suggests that the input parameters in the water saturation evaluation should be reconsidered. The cementation exponent is affected by several factors including
lithology, porosity, type of pore system, tortuosity, shapes and sorting and packing of the particulate system. Therefore the m value is not a constant over a well, but varies depending on many physical parameters and lithological attributes of porous media. A practical correlation was developed for m as a function of porosity and lithology using measurement data of several fields in the area and a variable m from this correlation was created for all wells. Applying a variable m successfully reduces the amount of uncertainty in calculated water saturation.
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The Barik Sandstone Member, northern Oman: Stratigraphic traps and review of a tight gas play
The Barik Sandstone Member (Cambrian-Ordovician Haima Supergroup) in northern Oman is the most productive deep and tight gas unit in Oman. The majority of existing discoveries are conventional structural closures but much of the remaining potential resides in stratigraphic traps. The Barik Sandstone Member comprises a variety of reservoir facies within an overall continental braid-plain to marginal marine/offshore setting. Through time, the position of the Barik coastline oscillated across northern Oman. Better reservoir developments are associated with sand-rich, fluvial-dominated systems, contemporaneous with regional progradational events, and exhibit abrupt contacts with adjacent marine mud-prone intervals. These progradational units are probably a result of forced regression. Barik stratigraphic-trap configurations rely on the northerly pinchout of these sandstone systems. Major flooding surfaces, ichnofacies and magnetostratigraphy have assisted in defining a detailed intra-reservoir, regional correlation
framework for the barren beds of the Barik Sandstone Member. This framework gives some regional control on intra-Barik reservoir distribution and connectivity and facilitates improved understanding of local changes in palaeogeography, providing a correlation resolution of less than one million years. With limitations on the seismic definition of reservoir distribution regional, Barik well penetrations, integrated with outcrop studies, provide the main input into geological models for the Barik Sandstone Member and the basis for play maps. All data have been used in facies modelling, core-log calibration, depositional environment interpretation, provenance, palaeocurrent analysis and reservoir quality determination. These parameters have been mapped to generate play maps that assist in defining and testing the stratigraphic pinchout traps in the Barik Sandstone Member and in early appraisal activities in discovered stratigraphic traps.
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Bio-chronostratigraphy and sequence stratigraphic interpretation of the Triassic succession of Socotra Island, Yemen
More LessAlong the eastern coast of Socotra Island (Yemen) a 220-m-thick marine Triassic succession is rather well exposed. The succession rests on a crystalline basement of Proterozoic age and is truncated by Jurassic sediments with slight angular unconformity. The Triassic of Socotra was deposited on an epicontinental setting and sedimentation was mostly controlled by sea-level changes. Its peculiar feature is the unusually rich paleontologic record consisting of conodonts, ammonoids, brachiopods and megalodontid bivalves. Three stratigraphic sections were studied at Ras Momi and Ras Falanj. The lithology is dominated by marls and limestones, often organized into shoaling upward cycles. Dolomitization occurs in the upper part of the succession. From the lithostratigraphic point of view the succession is attributed to one formation, divided into two members. The lower member is mostly calcareous, while the upper member mainly consists of dolostones. The detection of sequence boundaries, transgressive and highstand systems tracts (TST and HST) allow the identification of five depositional sequences from Olenekian to Late Carnian age. The age of the first three cycles is especially wellconstrained with conodonts and ammonoids. The five depositional sequences can be well correlated with the Sharland et al. (2001, 2004) peri-Arabian sequences Tr30, Tr40, Tr50, Tr60, Tr70. However, the high-resolution conodont and ammonoid bio-chronostratigraphic data from Socotra allow the re-calibration of the age of sequences Tr40 and Tr50.
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Breakthrough team performance: Amplifying the impact on E&P teams
Authors Benoit Barbier and Victor LunarThe petroleum industry is faced with a significant set of challenges that include: (1) accelerating the discovery of reserves; (2) improved exploitation of proven reserves, be it by shortened time to first-oil production or improved recovery; and (3) maximizing production to infrastructure capacity for brownfields. At the same time, the industry needs to recognize and address the shortage of skilled professionals and to accelerate the training and knowledge transfer to the younger generation of professionals and future graduates. Breakthrough team performance, described as changing the way that teams work and collaborate, is what the industry should consider adopting. It could help overcome the current set of constraints and amplify the impact that technical professionals can have on business results. This is realized by delivering integrated drilling and production operations, maximizing team collaboration to overcome resource constraints and accelerating the exploration process. This presentation will describe some gamechanging technology and approaches that are drastically improve the way teams work and consequently the impact that they are having on the company’s bottom line. The real examples that are presented indicate that our industry is already well on its path towards breakthrough team performance.
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Use of interval pressure transient testing to improve reservoir characterization of Mauddud carbonate reservoir in Sabiriyah field, northern Kuwait
Authors Bodoor Baroon, Moudi Al-Ajmi and Hamad Najeh and Ealian Al-EnziThe front-tracking and monitoring of pattern waterflooding are crucial reservoir management practices in the Mauddud carbonate reservoir in Sabiriyah field, located in northern Kuwait. It is important to run the interval pressure transient testing (IPTT) in this reservoir in order to have a complete understanding of the vertical connectivity between the layers in conjunction with other geological and dynamical data. IPTT tests were run in the Mauddud Formation at different depths in selected newly drilled wells in order to obtain a representative reservoir Kv/Kh (vertical/horizontal permeability ratio). This is in order to understand the vertical connectivity between high-permeability zones and the surrounding less-permeable zones, to support the PLT (production logging tool) result, which shows large contributions from high-permeability thief zones. The test was run by producing-from or injecting-into one set of perforations, and measuring the pressure response at another set. It was important to investigate the dual-porosity behavior
and inter-connectivity between layers, if any, which was not observed during the pre-water flooding period. For field development and reservoir management, it is important to describe the layering in terms of the vertical communication between layers. The number and placement of both injection and production wells requires an accurate description of the layering. IPTT has been used to calibrate both log and core data, with the advantage of conducting these tests under real reservoir conditions. The test results were excellent; they indicated very good connectivity between the Mauddud layers, and provided useful and valuable information about the inter-layer connectivity, reservoir heterogeneities and anisotropy.
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AVO Response of a visco-elastic porous layer
By Sumana BasuDetermination of fluid characteristics in a petroleum reservoir from its seismic response is an interesting problem. For this purpose the amplitude-versus-offset (AVO) response of an oil-bearing formation must be computed. Amplitudes of seismic waves and reflection coefficients must be computed when seismic waves propagate in a viscoelastic porous medium. The existence of a slow P-wave, in addition to a normal-travelling P-wave and S-wave, in a porous medium that depends on such characteristics like fluid viscosity and permeability, has been predicted on theoretical grounds. Seismic waves suffer different degrees of attenuation while propagating through the Earth’s layers, especially in the presence of fluids in the pore spaces. The attenuation of waves makes
it imperative to consider all such media as visco-elastic, whether porous or non porous. A numerical experiment has been carried out to generate the synthetic AVO response of a porous viscoelastic formation underlying a porous elastic medium. The boundary problem has been solved, and the theoretical results have been cast into a form resembling Zoepprtiz’s equations for computation of reflection and transmission coefficients. The nature of reflection pulses associated with the slow P-wave have been investigated for fluids of different properties (density and viscosity). The objective is to be able to detect the type of fluid from some attribute of the pulse shapes and its variation with offset.
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The ups and downs of inter-bed multiple attenuation
More LessWe present a comprehensive discussion of the main steps involved in applying data-driven surface-related multiple attenuation (SMA) and inter-bed multiple attenuation (IMA) algorithms, illustrated with field data examples from the Middle East. Despite recent advances (e.g. Kelamis et al., 2002), inter-bed multiple attenuation continues to present a formidable problem due to sparsity of data acquisition, noise, statics and the difficulty in distinguishing between primaries and multiples in many geologic settings. We demonstrate that accurate identification of key multiple generators is an important first step in applying IMA and describe a vertical seismic profile (VSP) deconvolution technique that may be helpful in analyzing multiple-generation mechanisms. Based on this analysis, we apply both post-stack (1-D) and pre-stack (1.5-D) multiple attenuation. In the case of prestack multiple attenuation, we address the data regularization procedures necessary to reconstruct the regularly and densely sampled common mid-point (CMP) gathers that are required for successful application of IMA. We also show that surface-related multiple attenuation is an important step in the pre-stack case and discuss how to overcome statics-related problems that arise during the application of SMA. Finally, we describe the trade-offs involved in choosing adaptive subtraction parameters in areas with overlapping primaries and multiples. We conclude that in the target reservoir zone, the application of pre-stack CMP-domain, data-driven, multipleattenuation
methods resulted in significant structural interpretability improvements. The signal-to-noise ratio was further enhanced through an application of a novel post-processing curvelet-based coherent noise attenuation technique, described in detail in the companion
presentation by Neelamani et al.
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A new approach to reservoir zonation of the Dariyan Formation in an Iranian field
Authors Bijan Beiranvand and Ali Moallemi and Bita ArbabThe Dariyan Formation and its equivalent Shu’aiba Formation in the Gulf consist of microporous, slightly argillaceous algal, peloidal, and orbitolinids lime mudstone and wackestone and grain-dominated fabrics with abundant rudist and coral debris in buildups. The two formations were deposited in a shallow-marine to lagoonal environment. Because of their commercial importance, and lateral and vertical variations in lithofacies and reservoir properties, the both formations have been intensively studied. The present study is based on 29 m of core material from one well, more than 300 thin sections from six wells, petrophysical logs and data, scanning electron microscope (SEM) photomicrographs, X-ray diffraction (XRD) analysis, mercury injection capillary pressure (MICP) data and pore size distribution curves. This data was used to identify facies associations and reservoir rock types (non-reservoir, poor and moderate). These, in turn, were used to define nine reservoir zones as consistent with Alshrahan (1985). The scheme was placed in a sequence stratigraphic framework. Seven facies associations were attributed to four depositional environments as follows: lagoon, leeward shoal, shoal and open-marine.
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Charge evaluation of the South Rub’ Al-Khali Basin, Saudi Arabia (Part I, for Part II see Nederlof et al.)
Authors Andrew Bell and Peter Nederlof and Walter VoggenreiterThe South Rub’ Al-Khali Company (SRAK) is exploring for gas and condensate in two contract areas which together encompass an area of approximately 200,000 square km. In order to quickly identify the most prospective areas in this large, yet relatively under-explored area, it was necessary in the first years of the venture to quantify the risk of source rock presence, the degree of maturation and predict the hydrocarbon mixture generated upon reaching maturity. Therefore, the regional geology of the Silurian-aged Qusaiba Formation was reviewed and the kinetic behaviour of the organic-rich shale was investigated in order to predict the likely phase of any hydrocarbon accumulation as well as the variations of condensate-to-gas ratios across the entire basin. The initial basin model identified the most prospective parts of the basin, and as more seismic data became available, the model was constantly updated. The kinetic behaviour of the Qusaiba Shales was measured using kerogen isolated from immature outcrop samples. Prior to the drilling of the first exploration well in 2006, predictions were made on the presence of source rock at the well location, its quality and the degree of maturation. This presentation will compare the outcome of the modeling with the actual well result, and is complimented by Part II (see Nederlof et al.)
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Monitoring variations in carbonate biofacies: Studies from Tertiary outcrops of Oman
More LessThe most complete succession of Tertiary carbonates in the Middle East is exposed along the southeastern Arabian Platform margin in Oman, which serves well for outcrop studies. The Late Paleocene-Early Eocene time slice involved widespread subsidence, extensive transgression over the Arabian Platform and aggradation of the first carbonate platform stage. The shallow-shelf environment is represented by the deposition of carbonates with alveolinid foraminifera, coralline algal nodules and scleractinian corals. In the Mid-Eocene, regional subsidence of the Arabian Plate was accompanied by extensive transgression and aggradation of the second carbonate platform stage. Thick nummulite shoals and banks accumulated along the platform margin. The Upper Eocene
calcarenitic shallow-shelf deposits are characterized by a rich macrofauna (molluscs, echinids and corals). In the Oligocene, the emergence of the Arabian Platform was related to the opening of the Gulf of Aden. Forced regression and shelf-margin platform progradation-aggradation developed at the edge of the Arabian Plate. Carbonate platform collapse and resedimentation along the margin occurred at the beginning of this stage. The limestones with marly and sandy intercalations contain patch reefs with scleractinian corals and an abundant macrofauna of echinoids, gastropods and bivalves. During the Tertiary mechanisms like climate, tectonic movements, eustatic sea-level changes and siliciclastic influx controlled the dimension and biofacies distribution
on the platform. These triggering mechanisms influenced the fauna (foraminifera) and flora (calcareous algae) during the different time-slices causing changes in the sedimentologic and biotic composition.
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Reservoir characterization and reservoir modeling of tight gas reservoir of Guangan field, China
By Fadila BessaThe Guangan field produces gas from a very thick Triassic sandstone reservoir that covers an area of 60 square km in southern China. A reservoir characterization study was undertaken to assist in proposing well locations. The model was based on geological, geophysical and engineering data available from 15 vertical and horizontal wells. This data was integrated and used to define different rock types of the sandstone reservoir based on to their reservoir properties. A static model using PetrelTM was used to visualize the reservoir distribution throughout the field. The interplay of initial composition, depositional environment and diagenetic overprint determine reservoir quality. Thin-section studies showed that the heterogeneity of the rock is controlled by grain size, pores, cementation and fractures. This results in a significant variation of reservoir characteristics. The importance of the varying diagenetic histories is that the major differences in initial composition and diagenesis are reflected in pore geometry, which controls reservoir properties. Flow-zones studies defined four zones that have similar fluid flow characteristics. The classification of these zones identified no-reservoir zones and the best reservoir zones in the rock. The defined reservoir zones have been compared to well-test results and production data. A net-sand model, based on seismic attributes, has been used to supervise the petrophysical model and flow-zone model. For the best exploitation we must choose the prime regions using 3-D models for locating new wells. The highest quality of the reservoir occurs in its upper part and recommended for coring, logging and perforation.
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Next-generation seismic imaging: High-fidelity algorithms and high-end computing
More LessFuture development of the Middle East’s hydrocarbon resources will include exploration in increasingly complex environments such as the Red Sea, necessitating increasing advances in computationally intensive imaging technologies for both exploration and exploitation. Among these technological advances, reverse time migration (RTM) yields the best possible images. RTM is based on the solution of the two-way acoustic wave-equation. This technique relies on the velocity model to image turning waves. These turning waves are particularly important to unravel subsalt reservoirs and delineate salt-flanks, a natural trap for oil and gas. Because it relies on an accurate velocity model, RTM opens new frontiers in designing better velocity estimation algorithms. The chief impediment to the large-scale, routine deployment of RTM has been a lack of sufficient computer power. RTM needs 30 times the computing power used in exploration today to be commercially viable and widely used. To overcome these challenges, the Kaleidoscope Project, a partnership between Repsol YPF, Barcelona Supercomputing Center, 3DGeo Inc. and IBM brings together the necessary components of modeling, algorithms and the uniquely powerful computing power of the MareNostrum Supercomputer in Barcelona to realize the promise of RTM, incorporate it into daily processing flows, and to help solve exploration problems in a highly cost-effective way. Uniquely, the Kaleidoscope Project is simultaneously integrating software (algorithms) and hardware (Cell BE), steps that are traditionally taken sequentially. This unique integration of software and hardware will accelerate seismic imaging by several orders of magnitude compared to conventional solutions running on standard Linux Clusters.
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Early grain-coat formation in modern eolian sands: Implications for prediction of deep porosity
Early-formed grain coats preserve favorable reservoir quality in deeply buried sandstones by inhibiting formation of high-temperature quartz cement during later burial. Deep eolian reservoirs with grain-coat-preserved porosity include the Norphlet, USA; Rotliegendes, Germany; and Unayzah, Middle East. Petrographic observations and quartz-cement modeling indicate that coat effectiveness in cement inhibition increases with greater coat continuity. Infiltrated/illuviated clays, diagenetic clays, and microcrystalline quartz all have been shown to form effective grain coats. Consequently, reliable deep-porosity prediction requires accurate models for the presence, continuity, and composition of early grain coats. A joint Saudi Aramco-ExxonMobil study was
undertaken to document the distribution and genesis of grain coats in modern eolian settings. Water and sand samples were collected from a range of depositional environments in arid and semi-arid settings (Saudi Arabia and New Mexico, respectively). Coat characteristics were evaluated using petrographic analyses and laboratory experiments. Early results indicate that most continuous infiltrated coats in eolian environments are clay, formed either by percolation of muddy water into wadi sediments, or illuviation of airborne dust into dunes and sand-sheets during early soil formation. Coated grains blown from wadis or soils into active dunes lose their coats by abrasion during eolian transport. Climate appears to be a control on coat formation and preservation. In arid climates, dunes remain active, and illuviated coats are abraded more quickly than they can form. Dunes and sand-sheets in semi-arid settings, however, are stabilized during wetter climatic periods. This stabilization allows longer-term illuviation and drives a multicyclic process of coat formation and abrasion.
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Wavepath tomography for complex velocity areas
Authors Dimitri Bevc, Moritz Fliedner and Morgan Brown and Biondo BiondiIn complex velocity models, such as below rugose salt bodies, wavefield continuation migration is usually superior to Kirchhoff methods because of multi-pathing, sharp velocity contrasts and the band-limited nature of seismic-wave propagation. Wavepath tomography offers a way to build the velocity model in a manner that is consistent with the migration operator. Instead of tracing rays to backproject residual velocities, a wavepath is constructed using the actual wavefield continuation operator. The operator represents the wave propagation between surface source-receiver pairs and subsurface reflection points by multiplication of impulse responses downgoing from the surface location and upgoing from the reflection point. The size of the inversion matrix is
kept to a manageable size by restricting the wavepath to the first Fresnel zone. The considerable expense of computing a single wavepath kernel can be partially offset in comparison to ray tomography, by the smaller number of backprojections that are required to sample the velocity model adequately. To streamline the velocity-model updating process, we have implemented an automatic method of signal detection that eliminates the need for manual reflector picking by scanning the seismic data volume with prediction-error filters and automatically selecting back-projection points based on dip coherency and semblance strength. This approach can save months of human time on a typical 3-D seismic imaging project and, thereby, shortens seismic imaging project turnaround time while exploiting the full redundancy of the recorded data.
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Predicting pore types in Khuff reservoirs: A step towards improved permeability predictions
By Ian BillingThe Upper Permian Khuff-B reservoirs of Saudi Arabia are prolific gas producers, with much of the production coming from stacked grain-rich shoals. While such stacked shoals often have excellent primary inter-particle porosity, this is frequently superseded by a phase of pore cementation and grain leaching. Thus, ooid- and peloid-rich reservoirs are frequently characterized by oo- or pel-mouldic pore systems. Such pore systems may contain significant hydrocarbons but connectivity may be limited due to the isolated nature of these pores. The detection of the relative abundance of poorly connected oo-mouldic porosity is essential for applying accurate porosity-permeability transforms. This study investigated the use of conventional wireline log data to identify relative percentages of well-connected and poorly-connected pore systems in Khuff-B reservoirs. Detailed core descriptions were carried out on two calibration wells, producing digital tracks of five major classes of pore types. Careful depth matching and correlation
with reprocessed wireline logs created a highly constrained dataset. A combination of sonic, density and neutron logs produced predictive algorithms which identified calibrated zones of poorly connected porosity. Blind-testing of these same algorithms on a wireline log suite from a third Khuff-B well produced a very good match. Ongoing work is now investigating the transform from pore-type distribution to improved permeability predictions. These new algorithms act as a proxy for creating boundaries to the permeability distributions; the resultant transforms match the datasets significantly better than a simple linear transform method, and can be routinely used as part of the process of Khuff-B reservoir assessment.
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An integrated approach to determine flow units in a complex Jurassic carbonate “Marrat” Reservoir in Burgan Oil Field, Kuwait
More LessThe carbonates of the Marrat Formation in the Magwa area of Kuwait’s Greater Burgan oil field were deposited in a shoal lagoonal complex, essentially in a ramp-to-rim environment. An inferred highstand systems tract holds substantial oil reserves in the middle Marrat reservoirs. The upper and lower Marrat are argillaceous with poor reservoir characteristics. This reservoir starting producing in 1984 and its depletion was driven with very little aquifer support. However, because asphaltene flocculation with pressure drop inhibit smooth production, a water-injection program is planned. It is therefore critical to understand the reservoir geology and flow units in order implement the program. An integrated approach was adopted which included: (1) rock-type transforms to quantifiable petrophysical based flow units; (2) sequence stratigraphic framework; and (3) laboratory-derived continuous porosity and permeability data from a well. The study established three flow units within the reservoirs. The graphical tools used to determine the flow units were: (1) Winlands porosity-permeability cross-plot, (2) stratigraphic flow profile, (3) stratigraphic modified Lorenz plot, and (4) cumulative flow and storage capacity. This well-proven methodology for identifying flow units will provide the basis for the water injection and perforation strategy and will influence the future business decision strategy for a successful water-flooding program.
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Preserved amplitude processing of complex transitional zone 2-D seismic
Authors Rodney Blackford and Ding Yenn Maa and Abdulaziz Al-FaresThis presentation provides a sequence of results on relative amplitude processing and interpretation of complex transitional zone 2-D seismic data in the Arabian Gulf. Interpretation of the previous seismic data revealed dynamic mistie problems, which were caused by phase matching of seismic from several different energy sources, geophones and recording systems, as well as multiples and refraction static corrections. Low-relief structures and stratigraphic traps are the primary targets, and therefore the seismic data needed to be processed while preserving relative amplitude. This would permit inversion processing to image the structures as well as provide wavelet processing for seismic stratigraphy. Dynamite, mud-gun and air-gun sources were phasematched to vibroseis to approximate zero-phase the data prior to the refraction static evaluation and calculations. A relative amplitude-consistent processing sequence of the data was applied throughout. The minimum amount of noise attenuation was used to achieve a balance between enhancing the signal-to-noise ratio, while preserving amplitude. A surface-consistent, triple-gate, second-zero crossing, predictive gap deconvolution was applied to avoid boosting the amplitude of multiples by whitening effects of a spiking deconvolution. Post-stack time migration (PSTM) was applied for additional enhancement of the signal, which improved the apparent post-stack frequency by reducing wavelet smearing in the stack process. Improved seismic to well log ties will be shown as well as solving the seismic mistie problems in the interpretation of events.
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Best practices in static modeling of giant carbonate reservoirs, onshore Abu Dhabi, United Arab Emirates
Authors Gérard Bloch, Shamsa Al Maskary and Luis Ramos and Avni S. KayaOver the last few years, the static reservoir modeling effort in ADCO has been significantly increased. Larges carbonate reservoir models have been either updated or generated for the first time. These models cover areas of 500–2,000 square km and reservoir thicknesses in the range of 15–450 ft. Average grid size of 50–250 m in the X and Y directions and 1–5 ft in the vertical axis are resulting in static model sizes of 2–40 million cells. The following practices have been shown to add considerable value to the static modeling effort: (1) integration of high-resolution sequence stratigraphy; (2) detailed definition of flow units, in line with dynamic requirement, captured in the static model as individual sub-zones; (3) geologically derived trend maps to constrain facies, thickness and porosity; (4) introduction of the shoulder bed concept to more accurately model reservoir property and avoid vertical leakages of properties; (5) thoroughcore description and integration of thin sections, poroperm and mercury injection capillary pressure (MICP) data to define reservoir rock types; (6) careful validation of core permeability data; (7) integration of core permeability values with well-test horizontal permeability (kh) and/ or Production Logging Tool (PLT) data where available and derivation of actual K multipliers; (8) replacement of permeability values honoring well test kh and/or PLT results in un-cored sections and considering them as additional hard K data to improve dynamic history-matching; (9) integration of log saturation using J functions to link saturation to porosity, permeability and reservoir rock types; (10) Power Law linking porosity to permeability and stochastic modeling of the residual permeability to capture heterogeneity; (11) systematic production of quality-control plots. Some of these practices are still being refined and feedback from the audience will be very much appreciated.
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