sequence stratigraphic
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2021 ◽  
Author(s):  
Subrata Chakraborty ◽  
Monica Maria Mihai ◽  
Nacera Maache ◽  
Gabriela Salomia ◽  
Abdulla Al Blooshi ◽  
...  

Abstract In Abu Dhabi, the Mishrif Formation is developed in the eastern and western parts conformably above the Shilaif Formation and forms several commercial discoveries. The present study was carried out to understand the development of the Mishrif Formation over a large area in western onshore Abu Dhabi and to identify possible Mishrif sweet spots as future drilling locations. To achieve this objective, seismic mapping of various reflectors below, above, and within the Mishrif Formation was attempted. From drilled wells all the available wireline data and cores were studied. Detailed seismic sequence stratigraphic analysis was carried out to understand the evolution of the Mishrif Formation and places where the good porosity-permeability development and oil accumulation might have happened. The seismic characters of the Mishrif Formation in dry and successful wells were studied and were calibrated with well data. The Mishrif Formation was deposited during Late Cretaceous Cenomanian time. In the study area it has a gross thickness ranging from 532 to 1,269 ft as derived from the drilled wells; the thickness rapidly decreases eastward toward the shelf edge and approaching the Shilaif basin. The Mishrif was divided into three third-order sequences based on core observations from seven wells and log signatures from 25 wells. The bottom-most sequence Mishrif 1.0 was identified is the thickest unit but was also found dry. The next identified sequence Mishrif 2.0 was also dry. The next and the uppermost sequence identified as Mishrif 3.0 shows a thickness from 123 to 328 ft. All the tested oil-bearing intervals lie within this sequence. This sequence was further subdivided into three fourth-order sequences based on log and core signatures; namely, Mishrif 3.1, 3.2, and 3.3. In six selected seismic lines of 181 Line Km (LKM) cutting across the depositional axis, seismic sequence stratigraphic analysis was carried out. In those sections all the visible seismic reflectors were picked using a stratigraphic interpretation software. Reflector groups were made to identify lowstand systems tract, transgressive systems tract, maximum flooding surface, and highstand systems tract by tying with the observations of log and core at the wells and by seismic signature. Wheeler diagrams were generated in all these six sections to understand the lateral disposition of these events and locales of their development. Based on stratigraphic analysis, a zone with likely grainy porous facies development was identified in Mishrif 3.0. Paleotopography at the top of Mishrif was reconstructed to help delineate areas where sea-level fall generated leaching-related sweet spots. Analysis of measured permeability data identified the presence of local permeability baffles affecting the reservoir quality and hydrocarbon accumulation. This study helped to identify several drilling locations based on a generic understanding of the Mishrif Formation. Such stratigraphic techniques can be successfully applied in similar carbonate reservoirs to identify the prospect areas.


2021 ◽  
Author(s):  
Christopher Gravestock ◽  
Alex Bromhead ◽  
Mike Simmons ◽  
Frans Van Buchem ◽  
Roger Davies

Abstract The Mesozoic stratigraphy of the Middle East is endowed with multiple world-class, economically significant petroleum systems. Since the first discovery of a major oilfield in an anticline structure in 1908 (Masjed-e-Suleyman, Iran), exploration and production in the Middle East has been largely focussed on relatively low-risk, large structural traps. However, across the Arabian Plate, unexplored structural traps at similar scales are becoming scarce. Therefore, in this mature petroleum province, attention must now focus on identifying the presence of subtle stratigraphic traps, especially within the hydrocarbon-rich Mesozoic stratigraphy. In order to locate and evaluate subtle stratigraphic traps, we have applied sequence stratigraphic principles across the Mesozoic strata of the Arabian Plate. This approach provides a regional, robust age-based framework which reduces lithostratigraphic uncertainty across international boundaries and offers predictive capabilities in the identification and extent of stratigraphic plays. Herein, we focus on three intervals of Mesozoic stratigraphy, namely Triassic, Middle-Late Jurassic and middle Cretaceous strata, in which regional sequence stratigraphic based correlations have identified stratigraphic trap potential. Each of these stratigraphic intervals are associated with the following stratigraphic traps:Triassic: Sub-crop traps associated with a base Jurassic regional unconformity and intra-Triassic unconformities. Onlap geometries associated with differential topography on the Arabian Plate.Middle-Late Jurassic: Pure stratigraphic trap geometries associated with basin margin progradation and pinch-out plays either side of the Rimthan Arch related to late Oxfordian/early Kimmeridgian sea-level fall.Middle Cretaceous: Sub-crop potential beneath the regional mid-Turonian unconformity, basin margin progradation and stratigraphic pinch-out geometries associated with onlap onto basin margins. This regional sequence stratigraphic approach highlights the remaining exploration and production opportunities within these hydrocarbon-rich stratigraphic intervals.


2021 ◽  
Author(s):  
◽  
Joanna Eveline Grace Elliott

<p>The Hautawa Shellbed, Whanganui Basin is described in detail to uncover lateral variations in depositional paleoenvironment. This was achieved through the in situ documentation of the macrofaunal assemblage and its taphonomic attributes at three localities. The sites from west to east are: Ridge Road, Old Hautawa Road, and the type section on West Road. They are all exposures on farm tracks and cover a 20-km range across the central Whanganui Basin. The descriptions were collected at 15-cm intervals and analysed using k-means clustering and Principal Component Analysis (PCA) to uncover trends within the data set. Combining the assemblage data with the taphonomic has allowed six major biofacies to be recognised. In turn, the arrangement of the biofacies in the sections suggest three subunits: A, B, and C. Subunits A and C are laterally continuous between all of the sections and always relate to the lowermost and upper-most portions of the Hautawa Shellbed. In contrast, subunit B is only observed to occur at West Road overlying subunit A. These subunits have can also be equated to sequence stratigraphic terminology. Subunits A and B form an onlap shellbed and subunit C a backlap shellbed. Hence, the Hautawa Shellbed represents deposition during the transgressive systems tract of a single cyclothem. This study is unique compared to other Whanganui Basin stratigraphic research in its statistically robust approach for comparing data gathered at various sites along outcrop strike to better understand the preserved paleoenvironment. To support the macro-faunal investigation, census counts of foraminifera were conducted for samples collected from the fine-grained sediments encompassing the Hautawa Shellbed at each of the three sites. Together, the macrofaunal and foraminiferal studies reveal temporal and spatial paleoenvironmental changes within the Hautawa Shellbed. The presence of biostratigraphically important fauna within the Hautawa Shellbed has been used to link the unit to other similar formations in both the Whanganui and East Coast Basins. This key assemblage which highlights the Nukumaruan-Mangapanian Stage boundary at 2.40 Ma includes: Zygochlamys delicatula, Crassostrea ingens, Phialopecten thomsoni, Phialopecten triphooki, and Mesopeplum convexum. The paleoenvironmental variations observed and presented here for the Hautawa Shellbed have been combined with published work on other parallel formations to produce a paleogeographic map of the Whanganui Basin for 2.40 Ma.</p>


2021 ◽  
Author(s):  
◽  
Joanna Eveline Grace Elliott

<p>The Hautawa Shellbed, Whanganui Basin is described in detail to uncover lateral variations in depositional paleoenvironment. This was achieved through the in situ documentation of the macrofaunal assemblage and its taphonomic attributes at three localities. The sites from west to east are: Ridge Road, Old Hautawa Road, and the type section on West Road. They are all exposures on farm tracks and cover a 20-km range across the central Whanganui Basin. The descriptions were collected at 15-cm intervals and analysed using k-means clustering and Principal Component Analysis (PCA) to uncover trends within the data set. Combining the assemblage data with the taphonomic has allowed six major biofacies to be recognised. In turn, the arrangement of the biofacies in the sections suggest three subunits: A, B, and C. Subunits A and C are laterally continuous between all of the sections and always relate to the lowermost and upper-most portions of the Hautawa Shellbed. In contrast, subunit B is only observed to occur at West Road overlying subunit A. These subunits have can also be equated to sequence stratigraphic terminology. Subunits A and B form an onlap shellbed and subunit C a backlap shellbed. Hence, the Hautawa Shellbed represents deposition during the transgressive systems tract of a single cyclothem. This study is unique compared to other Whanganui Basin stratigraphic research in its statistically robust approach for comparing data gathered at various sites along outcrop strike to better understand the preserved paleoenvironment. To support the macro-faunal investigation, census counts of foraminifera were conducted for samples collected from the fine-grained sediments encompassing the Hautawa Shellbed at each of the three sites. Together, the macrofaunal and foraminiferal studies reveal temporal and spatial paleoenvironmental changes within the Hautawa Shellbed. The presence of biostratigraphically important fauna within the Hautawa Shellbed has been used to link the unit to other similar formations in both the Whanganui and East Coast Basins. This key assemblage which highlights the Nukumaruan-Mangapanian Stage boundary at 2.40 Ma includes: Zygochlamys delicatula, Crassostrea ingens, Phialopecten thomsoni, Phialopecten triphooki, and Mesopeplum convexum. The paleoenvironmental variations observed and presented here for the Hautawa Shellbed have been combined with published work on other parallel formations to produce a paleogeographic map of the Whanganui Basin for 2.40 Ma.</p>


Author(s):  
Haris Ahmed KHAN ◽  
Ali Asghar SHAHID ◽  
Muhammad Jahangir KHAN ◽  
Taher ZOUAGHI ◽  
Maria Dolores ALVAREZ ◽  
...  

Author(s):  
Alireza Asadi ◽  
Hossain Rahimpour-Bonab ◽  
Mohsen Aleali ◽  
Mehran Arian

AbstractIn this study, our attempt is to integrate sedimentological and petrophysical data for reservoir evaluation in the sequence stratigraphic framework. Petrographic analysis of the Late Jurassic–Early Cretaceous Fahliyan Formation reservoirs of two oilfields in the northwest of the Persian Gulf led to recognition of twelve microfacies. They can be classified into four facies associations, including open marine, shoal, lagoon and tidal flat, which are deposited in a homoclinal ramp carbonate. Sequence stratigraphy of the studied successions led to the recognition of three third-order depositional sequences based on vertical changes in microfacies and gamma ray analysis. Except for the upper boundary of the third sequence, the other sequence boundaries are type I (SBT.1). Dissolution is the most important diagenetic feature that affected the lower depositional sequence which is caused by the development of subaerial exposure after the deposition of the Fahliyan Formation, whereas cementation is the main diagenetic feature affecting the second- and third depositional sequences, causing their lower reservoir quality. In order to identify the flow units, the flow zone index methods, porosity throat radius (R35) and modified Lorenz based on stratigraphy were applied. The key wells studied in this area have shown good correlation throughout the studied oilfields which may potentially be used for hydrocarbon exploration and field development in the Late Jurassic–Early Cretaceous deposits of the Persian Gulf. This study integrates geological and petrophysical data (rock typing) toward sequence stratigraphic framework.


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