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Abstract The Early Cretaceous Kharaib Formation is one of the most prolific hydrocarbon bearing reservoirs in the Middle East. Based on sedimentary characteristics, the Kharaib Formation is divided into three main intervals/zones: the lower, middle and upper Kharaib. Interpretation of the depositional fabrics and prediction of reservoir parameters is often difficult due to the Kharaib Formation's diverse array of sedimentary characteristics. To address the considerable heterogeneity of the Kharaib Formation, this study investigates depositional characteristics and the diagenetic impact on reservoir quality within the Sajaa Field. The Kharaib Formation sediments were characterized using a Dunham/Embry & Klovan (1971) defined classification scheme. Analytical techniques via thin section analysis, scanning electron microscopy (SEM) and capillary pressure data were used to qualitatively and semi-quantitatively assess porosity and the diagenetic processes involved in its evolution. Key reservoir quality parameters for Kharaib intervals were defined by combining petrographic analysis and conventional core methods. The sedimentological characterization of the Kharaib sediments in the Sajaa Field showed a range of Orbitolina-bearing carbonate textures, which were interpreted as inner-ramp deposits. The stacking pattern of the depositional facies showed intermediate-order trends. The conventional core analysis measurements showed poor to good reservoir properties with porosity values of 0.7 – 23.2% and permeability values from negligible to 2 – 3 md. The pore system is dominated by grains and matrix-hosted micropores, which are primarily generated via diagenesis. Qualitative thin section analysis identified grain-hosted micropores as the most significant microporosity type, highlighting that grain-rich textures are relatively more porous compared to mud-rich textures. Diagenesis transformed both the matrix and various grain types (e.g., micritized grains, foraminifera etc.), generating considerable micropore volume. High resolution SEM imaging, along with semi-quantitative assessment, highlighted that diagenetic modification of the micritic sediments led to an abundance of sub-rounded to polyhedral crystals exhibiting primarily sub-punctic to punctic intercrystalline contacts that generated a porous fabric. Mercury injected capillary pressure (MICP) data, confirmed the abundance of micropores within the pore size distributions of studied samples. This study demonstrates the importance of considering textural variation within the Kharaib Formation when assessing the reservoir coupled with the fractured nature of the unit. The established microporosity-depositional relationships when combined with the updated core descriptions now allow for the integration of textural trend information in the field that can be applied to refine reservoir property and abundance distributions.
- Asia > Middle East > Saudi Arabia (1.00)
- Asia > Middle East > UAE > Sharjah Emirate > Sharjah (0.42)
- Asia > Middle East > UAE > Sharjah Emirate > Arabian Gulf (0.41)
- Research Report > Experimental Study (0.87)
- Research Report > New Finding (0.68)
- Geology > Sedimentary Geology > Depositional Environment (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (1.00)
- Geology > Geological Subdiscipline > Stratigraphy (1.00)
- Asia > Middle East > UAE > Sharjah > Oman Mountains Foldbelt Basin > Sajaa Field > Thamama Group Formation (0.99)
- Asia > Middle East > Saudi Arabia > Thamama Group > Kharaib Formation (0.99)
- Asia > Middle East > Bahrain > Awali Field (0.99)
- Asia > Middle East > Saudi Arabia > Thamama Group > Shu'aiba Formation (0.94)
Effects of Diagenesis and Depositional Settings on the Reservoir Quality of the Barremian-Aptian, Kharaib Formation: A Case Study from the Bahrain Field, Kingdom of Bahrain
Bardalaye, Jayanta (Tatweer Petroleum) | Almuntaser, Ali (Tatweer Petroleum) | Jaber, Ibrahim (Tatweer Petroleum) | Phukan, Madhujya L. (Schlumberger) | Siddiqi, Saad A. (Schlumberger) | Raina, Ishan (Schlumberger)
Abstract The Barremian-Aptian, Kharaib Formation is among the main reservoir units in the Middle-East. The Kharaib Formation is broadly divisible into three main zones: the Upper, Middle and Lower Kharaib, which are defined based on their distinct sedimentological characteristics. The Kharaib interval has been extensively studied across the region; however, the inherent heterogeneity associated with sediments always makes it challenging for interpretation of the depositional facies, stratal geometries, and the prediction of their reservoir properties. This study focuses on the Middle and Upper Kharaib by integrating sedimentological, diagenetic, and pore-scale datasets to provide a better understanding of the depositional framework, diagenesis and its effects on the reservoir properties. Dunham/Embry & Klovan classification (1971) scheme is used to describe the sediments, which determines lithofacies. Lithofacies that are genetically relatable are grouped into larger sets of associations. The lithofacies association represent their sedimentary environments of deposition. The grouping/stacking pattern of the sediments reflects a broad third-order sequence. Higher-order variations/sequences are either from localized topographical changes or energy variations or from sea-level changes, which thereby imparts lateral reservoir heterogeneity. X-ray diffraction (XRD) analysis defines the mineralogical composition, whereas pore-scale fabric/textural characteristics have been defined via conventional light microscopy and scanning electron microscopy (SEM). Sedimentological description of the Kharaib Formation showed varying textures ranging from mudstone to grain-rich floatstone, which are interpreted to be deposited in a broad homoclinal ramp setting. Petrographic evaluation of the sediments from the studied section highlighted the effects of diagenesis on reservoir properties with calcite cementation significantly reducing the reservoir quality (i.e., lower porosity and permeability). In contrast considerable micro and macropore enhancement due to secondary dissolution appears to negate the effects of cementation. In the studied sediments, the porosity comprises considerable abundance of primary and secondary macropores. The measured porosity varies from moderate to very good, while permeability is low to moderately high. Interrogation of conventional core analysis data establishes that the primary control on reservoir quality distribution is sediment texture and composition. The genetically distinct characteristics of lithofacies related to allochem assemblage, their abundance and size aid in defining the associations, which thereby provides the former fabric for the subsequent diagenetic alterations. The abundance of detrital clays in the middle Kharaib appears to be the primary cause of relatively poor reservoir quality. This study shows that both the original depositional texture/composition and diagenesis have had an important impact on shaping reservoir properties. This integrated approach sheds light on the sedimentological make-up, depositional setting, and diagenetic overprint of the Kharaib Formation and their effect on the reservoir quality of various lithofacies. This understanding will further develop work related to pattern prediction of the Kharaib Formation, which may be extrapolated to uncored intervals for reservoir quality correlation and assessment.
- Asia > Middle East > Saudi Arabia (1.00)
- Asia > Middle East > Bahrain (1.00)
- North America > United States > Texas > Terry County (0.40)
- Research Report > Experimental Study (0.89)
- Research Report > New Finding (0.54)
- Geology > Sedimentary Geology > Depositional Environment (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (1.00)
- Geology > Geological Subdiscipline > Stratigraphy (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.52)
- Asia > Middle East > Saudi Arabia > Thamama Group > Kharaib Formation (0.99)
- Asia > Middle East > Kuwait > Ahmadi Governorate > Arabian Basin > Widyan Basin > Ratawi Formation (0.99)
- Asia > Middle East > Bahrain > Awali Field (0.99)
- (2 more...)
Seismic Stratigraphy and Depositional Evolution of the Mishrif Formation in Western Onshore Abu Dhabi
Perrotta, S.. (Shell International B. V.) | Zampetti, V.. (Shell International B. V.) | Chaari, G.. (Shell International B. V.) | Krayenbuehl, T.. (Shell International B. V.) | Braun, M.. (Shell International B. V.) | Franco, B. J. (ADNOC) | Neves, F.. (ADNOC) | Kobaisi, A. Saad (ADNOC)
Abstract A sequence stratigraphic study of the Cenomanian-early Turonian Mishrif Formation has been carried out in the SW of the United Arabian Emirates (UAE) in order to understand the evolution of the reservoir distribution and occurrence of potential stratigraphic and diagenetic traps in the UAE. The study has used an integrated reservoir approach that includes regional geology, seismic stratigraphy together with well data. The use of the core data and logs has allowed identification of facies changes, key stratigraphic surfaces and a number of a few feet thick dense intervals that show a relatively high lateral correlatibility, which appear to be below the seismic resolution. The use of seismic attributes together with the well calibration has been crucial to define seismic facies and their lateral and vertical distribution. Results from this study allowed recognition of several smaller scale 3 order cycles, which are comprised in a larger 2 order genetic sequence. Each small-scale cycle is bounded by a sequence boundary overlain by a flooding event made up of a thin dense interval which shows an increase in argillaceous content and locally chert. These sequences are characterised by an eastward progradation from muddy inner ramp facies passing upwards to rudist-rich patch reef/mixed skeletal shoal complexes developed in an inner to mid-ramp depositional setting. This latter setting appears to be best developed in the uppermost large-scale sequence, below the regional unconformity that separates the Mishrif from Ruwaydha and Tuwayil formations. Highly porous facies appear to decrease seismic velocity. The integrated approach presented here captures the variety in depositional environments, architecture, geometry and reservoir heterogeneity, which results in higher likehood to identify stratigraphic and diagenetic traps. Furthermore, the recognition of seismic characteristics of the Mishrif reservoir may be used as a tool to predict the distribution and evolution of units that create velocity variations in the Mishrif Formation and which affect the structural definition of deeper reservoirs as the Shuaiba Formation.
- Asia > Middle East > Qatar > Arabian Gulf (0.84)
- Asia > Middle East > UAE > Abu Dhabi Emirate > Abu Dhabi (0.51)
- Phanerozoic > Mesozoic > Cretaceous > Upper Cretaceous > Cenomanian (0.49)
- Phanerozoic > Mesozoic > Cretaceous > Upper Cretaceous > Turonian (0.49)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (1.00)
- Geology > Geological Subdiscipline > Stratigraphy (1.00)
- Geology > Sedimentary Geology > Depositional Environment > Marine Environment > Reef Environment (0.50)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.35)
- Geophysics > Seismic Surveying > Seismic Processing (0.94)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.34)
- Asia > Middle East > Qatar > Thamama Group > Shu'aiba Formation (0.99)
- Asia > Middle East > Qatar > Arabian Gulf > Arabian Basin > Arabian Gulf Basin > Block 6 > Al Khalij Field > Mishrif Formation (0.99)
- Asia > Middle East > Iraq > Basra Governorate > Arabian Basin > Widyan Basin > Mesopotamian Basin > Zubair Field > Zubair Formation (0.94)
- (5 more...)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Sedimentology (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Geologic modeling (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
Abstract An extensive play review was carried out of the Mishrif Formation in Abu Dhabi. The database existed of almost 3000 2D seismic lines and 28 3D seismic surveys, complemented by 450 wells, out of which 260 had reliable time-depth data. The study resulted in Abu Dhabi-wide depth and thickness maps and a good overview of the Shilaif basin development and Mishrif reservoir distribution. The Mishrif Formation in Abu Dhabi comprises the progradational shelf margin facies which is a time equivalent of the corresponding Shilaif basinal facies. The Mishrif development in the UAE is strongly asymmetric. The western Mishrif platform sediments are characterized by stacked clinoforms comprising clean, high-energy carbonates. Rudist reefs and grainstone shoals along the successive shelf edges, which form those clinoforms, generally have good reservoir properties. Similar favorable reservoir characteristics can also be found in isolated platforms and grainstone beds which are locally well developed in lagoonal settings found behind the shelf edges. In the east, the Mishrif is generally much thinner and is characterized by more differentiated, coarsening and shoaling-upwards sequences, each grading from fine basinal wackestone to medium/coarse-grained shallow marine packstone. This indicates sedimentation on a shallowing depositional slope. This slope lithofacies is made up of dark-colored, very fine- to fine-grained, well sorted, bioclastic packstones, grading into lighter colored, medium-grained, unsorted, bioclastic packstones to grainstones. High-quality reservoir facies occur only near the prograding shelf edges and over salt domes from which build-ups may have nucleated. Kerogen carbon isotope values and GC-MS fingerprints confirm that the Shilaif Formation is the source of the Mishrif oils. The Shilaif Formation is immature over large parts of Abu Dhabi, notably the western offshore part of the Emirate. In the deeper salt-withdrawal basins such as the West Bu Hasa and Falaha synclines the source rock is oil-mature and also in the Oman Mountain foreland basin, grading to gas mature further towards the east. In most of the mature Shilaif kitchens, oil generation commenced during Miocene times, in the southern offshore part of Dubai it may have started as early as the Early Oligocene. The Mishrif Play prospectivity evaluation will guide future appraisal drilling and will serve as a basis for further exploration activities related to conventional and unconventional trapping styles in the Formation.
- Asia > Middle East > UAE > Abu Dhabi Emirate > Abu Dhabi (1.00)
- Asia > Middle East > Qatar > Arabian Gulf (0.91)
- Phanerozoic > Mesozoic > Cretaceous > Upper Cretaceous > Turonian (0.64)
- Phanerozoic > Mesozoic > Cretaceous > Upper Cretaceous > Cenomanian (0.50)
- Phanerozoic > Mesozoic > Cretaceous > Lower Cretaceous > Albian (0.50)
- Phanerozoic > Mesozoic > Cretaceous > Lower Cretaceous > Aptian (0.40)
- Geology > Sedimentary Geology (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (1.00)
- Geology > Geological Subdiscipline (1.00)
- (2 more...)
- Asia > Middle East > Qatar > Thamama Group > Shu'aiba Formation (0.99)
- Asia > Middle East > Qatar > Arabian Gulf > Arabian Basin > Arabian Gulf Basin > Block 6 > Al Khalij Field > Mishrif Formation (0.99)
- Asia > Middle East > Qatar > Arabian Gulf > Arabian Basin > Arabian Gulf Basin > Block 6 > Al Khalij Field > Laffan Formation (0.99)
- (3 more...)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Sedimentology (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Geologic modeling (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
Abstract Objectives/Scope This study focuses on assessing the uncertainties related to sedimentological heterogeneity and the diagenetic variability within the gas-condensate reservoirs of the Shuaiba Formation, Sharjah, United Arab Emirates. Methods, Procedures, Process For characterizing the sedimentology of the Shuaiba Formation, a lithofacies scheme has been developed on the basis of Dunham's (1962) and Embry & Klovan classification (1971). The lithofacies are grouped on the basis of their genetic relationships which also correspond to their depositional environment, and are designated as lithofacies associations. A pore-scale fabric/textural investigation was completed using conventional thin-section microscopy and Scanning Electron Microscopy (SEM). Results, Observations, Conclusions The Shuaiba sediments are characterized by skeletal-rich wackestone/packstones to floatstones deposited in an inner ramp setting. The stacking pattern of the inner ramp deposits define broad third order trends observed across the studied field.These trends are relatable to the regional sequence stratigraphic framework of Sharland et al. (2001). In higher order sequences, lateral variations in lithology occur, defining the reservoir heterogeneity, which are most likely forced by topographic/hydrodynamic variation as well as sea level changes. Reservoir quality distribution is controlled by various factors, including the depositional texture and allochem assemblage (abundance, type, and size). Diagenetic alteration of the textures played an important role in determining overall reservoir quality. The pore enhancing phases are defined by dissolution events, where later stage dissolution was the dominant phase to enhance micropores and also to create meso- to macropores which partially to completely negated the effect of previous cementing phases. In these Shuaiba deposits, the porosity comprises common matrix-hosted as well as grain-hosted micropores along with variably distributed intraparticle and rare mouldic meso- to macropores. The measured porosity ranges from very poor to moderate (0.5-17%) while permeability is very low to low (<0.001-1.49 mD). The detailed petrographic analysis highlighted that changes in micritic fabric shows a variation in the reservoir properties. From SEM observations, it was noted that microcrystalline calcite crystals of polyhedral to sub-rounded morphologies with intercrystalline contacts ranging from facial to sub-punctic, which display relatively a good microporosity developement, whereas crystals that show anhedral compact character with coalescent/fused intercrystalline contacts are rarely associated with any microporosity. Novel/Additive Information In addition to SEM characterization, porosity data and elastic properties (e.g., Young's moduli) generated from the interpretation of the well-log data, were used to investigate the prospective relationship between the microporous carbonates and elastic properties. The comparisons highlight that an increase in porosity values results in a decrease of Young's moduli values, thereby reflecting a decrease in the stiffness of the rock. On the other hand, the increase in porosity maybe linked to the evolution of anhedral, compact, micritic fabric to polyhedral/sub-rounded micritic fabric. The understanding of this relationship provides a powerful tool to be utilized in reservoir architecture prediction based on integrating the sedimentological framework and diagenetic overprint.
- Geology > Sedimentary Geology (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (1.00)
- Geology > Geological Subdiscipline > Stratigraphy (1.00)
- (2 more...)
- Europe > Denmark > North Sea > Danish Sector > Central Graben > Block 5604/29 > South Arne Field (0.99)
- Asia > Middle East > UAE > Thamama Group > Shu'aiba Formation (0.99)
- Asia > Middle East > UAE > Sharjah > Oman Mountains Foldbelt Basin > Sajaa Field > Thamama Group Formation (0.99)
- (3 more...)