bluuebunny/crossref_metadata_2025 huggingface dataset:
Lithostratigraphy, Sedimentology and Hydrocarbon Habitat of the Pre-Cenomanian Nubian Sandstone in the Gulf of Suez Oil Province, Egypt
Authors: Alsharhan Abdulrahman S. , Salah Mohammed G.
Published: October 2021

The Paleozoic-Lower Cretaceous Nubian Sandstone is a thick sequence of up to 1,200 meters of clastic and thin carbonate sediments. In ascending order it is classified into the following groups and formations: Qebliat Group, Umm Bogma Formation, Ataqa Group and El-Tih Group. This sequence is composed mainly of sandstones with shale and minor carbonate interbeds and was deposited in continental and fluviomarine to marine settings. Petrographically, two main facies of Nubian Sandstone can be recognized in the Gulf of Suez: quartzarenite and quartzwackes. Both contain subfacies that are different in their secondary components, cement and matrix types, reflecting their different depositional environments and diagenetic histories. The pre-Cenomanian Nubian Sandstone is one of the most prolific reservoirs in the Gulf of Suez oil province. These sandstones have intervals with good reservoir quality throughout the basin, with net pay thickness of up to 450 meters, and net sand ratios ranging from 60% to 90%. Porosity varies from 10% to 29%, and permeability from 70-850 millidarcies. The quality of the reservoir depends on its shaliness, diagenetic history and the depth of burial (compaction). The Nubian Sandstone still has a high potential as a reservoir, particularly in the northern sector of the Gulf of Suez where few wells have specifically targeted this interval.
Stratigraphy of the Lower Paleozoic Haima Supergroup of Oman
Authors: Droste Henk H.J.
Published: October 2021

Following the discovery of significant gas/condensate reserves in Lower Paleozoic clastics in Central Oman a regional geological review using all available well data and a set of regional seismic lines was carried out by Petroleum Development Oman. The objective of this study was to support further appraisal and exploration activities. A chronostratigraphic framework of regional correlatable major flooding surfaces improved the understanding of the stratigraphic relationship between the different units and the regional distribution of the reservoir seal pairs. The interval of interest, the Cambrian to Lower Silurian Haima Supergroup, is a late syn- to post-rift siliciclastic infill of an extensive graben system. The depositional setting was initially continental but higher in the sequence of marine deltaic setting prevailed. The sequence is characterised by the occurrence of laterally extensive sand sheets typical of pre-vegetational times but difficult to interpret sedimentologically. At least six major transgressive regressive cycles can be recognised which can be regionally correlated. Marine intercalations are limited to Central and North Oman. The clastic influx into the grabens was initially of local origin but as the grabens filled up the sediments were predominantly derived from a southern source.
Structural and Stratigraphical Setting of the Faiyah Range, Northwestern Oman Mountain Front, United Arab Emirates
Authors: Noweir M. Atef , Alsharhan Abdulrahman S. , Boukhary Mohamed A.
Published: October 2021

The Faiyah Range belongs to a group of regional ridges that formed by post-obduction folding of the Upper Cretaceous-Tertiary sedimentary rocks exposed along the western margin of the Northern Oman Mountains. The Faiyah Anticline, generally trends north-northeast to south-southwest with thrust faults striking parallel to the fold axis. The anticlinal hinge was later displaced by a dextral strike-slip fault, named here as the Faiyah Fault, into two segments. The northeastern segment includes Jebels Rumaylah, Faiyah and Mulayhah, and the southwestern segment includes Jebels Buhays and Aqabah. The anticline is interpreted to result from northeast-southwest compression during the Tertiary.

In the Faiyah Range the neoautochthonous sedimentary rocks are the Maastrichtian Qahlah and Simsima formations, and the Eocene Dammam Formation. Stratigraphic evidence shows that the lower part of the Qahlah was deposited in a non-marine environment while the upper part was deposited during a marine transgression. The Simsima was deposited in a shallow-marine environment. These units unconformably overlap the allochthonous Semail Ophiolite. The microfaunal content of the so-called Muthaymimah Formation (?Tertiary), of earlier authors, indicates that it is of Maastrichtian age in the Faiyah Range. This sequence is also conformable to the Simsima and therefore it is considered to be the upper member of the Simsima in this area.
Regional Structural Style of the Central and Southern Oman Mountains: Jebel Akhdar, Saih Hatat, and the Northern Ghaba Basin
Authors: Mount Van S. , Crawford Roderick I.S. , Bergman Steven C.
Published: October 2021

Three quantitative regional transects across the Saih Hatat and Jebel Akhdar anticlines in the Central and Southern Oman Mountains and the Northern Ghaba Basin have been constructed based on surface, well and seismic data. Interpreted large-scale structural geometries suggest that the Saih Hatat and Jebel Akhdar anticlines are basement-involved compressional structures, underlain by north-dipping, high-angle, blind, reverse faults located beneath their southern limbs. A compressional deformation event initiated in the Oligocene (constrained by apatite fission track data) involving the high-angle reverse faults is interpreted in which pre-Permian strata and Permian-through-Lower Cretaceous strata, exposed in the Saih Hatat and Jebel Akhdar anticlines, were parautochthonous - uplifted over the underlying reverse faults, and not displaced a great distance laterally. The allochthonous Hawasina and Sumeini sedimentary rocks and the Semail Ophiolite complex are interpreted to have been emplaced onto the carbonate platform during the Late Cretaceous, and have subsequently been parautochthonous during the Tertiary deformation.

The upper portion of the pre-Permian section in the Ghaba Basin consists predominantly of a thick (>4 kilometers) sequence of Cambrian-through-Silurian, predominantly non-marine to shallow-marine, clastics of the Haima Supergroup. In contrast, out of the Ghaba Basin proper in the Central Platform or Musallim High region, the Haima Supergroup is generally less than 2 kilometers thick, and interpreted to thin to the north. The fundamental difference in pre-Permian strata exposed in the Saih Hatat and Jebel Akhdar Anticline windows is the thick (>3.4 kilometers) section of Ordovician age, shallow-marine strata (Amdeh Formation) present in the Saih Hatat Anticline, but absent in the Jebel Akhdar Anticline. In our interpretation, the shallow-marine clastics exposed in the Saih Hatat Anticline represent the northern extension of the Early Paleozoic Ghaba Basin, which have been uplifted over a high-angle reverse fault in the Early Tertiary deformation event. The cross-section through Jebel Akhdar is located to the northwest of the Ghaba Salt Basin, along the Musallim High. In this area the thickness of the Ordovician strata deposited is interpreted to be less than in the Ghaba Basin. The Ordovician section is not present in the Jebel Akhdar structure - the thinned section likely eroded in a Late Paleozoic deformation event.
Plio-Quaternary Movement of the East Arabian Block
Authors: Weijermars Ruud
Published: October 2021

New data presented herein support the previously suggested existence of an East Arabian Tectonic Block in Saudi Arabia. However, the East Arabian Tectonic Block is not exclusively bound by grabens, as was previously thought, but also by strike-slip faults and transpressive folds (in what is named here the Mughrah-Al-Kharj Transpression Zone), which laterally grade into the transtensive Central Arabian Graben System. Evidence for Plio-Quaternary strike-slip motion is presented here for the first time and supports previous contentions that graben formation occurred in Plio-Quaternary time. These new observations allow the development of a tectonic model that succinctly explains the deformation along the margins of the East Arabian Block.

With the importance of regional fault structures thus recognized, even some major faults of tectonic dimensions start to emerge in the Eastern Province of Saudi Arabia. For example, radar images from the Space Shuttle Endeavour confirm that the Nisah Fault extends eastward along Wadi As-Sahba, over a total distance of 250 kilometers, which was previously undemonstrable. The Sahba Fault is made visible beneath the Ad-Dahna Sand Sea by virtue of the sand-penetrating capability of the L-band radar. Five to eight kilometers of left-lateral strike separation is visible on either side of Wadi As-Sahba which truncates the southern end of the Ghawar field. The graben structure of the Nisah Fault System had been reported before, but its eastward continuation and any strike separation were not established until now. Furthermore, the Nisah-Sahba Fault System may extend further eastward, beneath alluvial gravels, for an additional 200 kilometers to join a known lineament at the southern end of Qatar. Further extension towards the Gulf into the 600-kilometer long Trans-Arabian Gulf Fault is also suggested here for the first time.

Field evidence presented here indicates that a substantial part of the motion of the Central Arabian Graben System took place in the Plio-Quaternary and may continue at present. This has been inferred from a study of the wadi (flood valley) system on the Jubaila and Hanifa outcrops in the vicinity of the graben structures to the south of Riyadh. In fact, an 8-kilometer long section of a mature stream channel, known as Sha’ib al-Miklaf, which was formerly discharging intermittent wadi drift and torrential run-off waters into Wadi Hanifa, has now been cut off from its former catchment area by the graben tectonics. As a result Sha’ib al-Miklaf now lies idle between the active wadis of the Awsat Graben and the Nisah Graben. The occurrence of recent fault motion in the Arabian Platform is further supported by changes in thickness of the Ad-Dahna Sand Sea across the Sahba Fault, as well as by truncation of mega-barchanoids in the Jafurah Sand Sea across the Jaub lineament. Not surprisingly, some modern seismicity in the Eastern Province of Saudi Arabia may be attributed to motion on the Nisah-Sahba Fault System.
A New Look at the Middle to Lower Cretaceous Stratigraphy, Offshore Kuwait
Authors: Al-Fares Abdul Aziz , Bouman Mark , Jeans Pete
Published: October 2021

Offshore exploration in Kuwait commenced in 1961 with the award of a 5,600 square kilometre offshore concession to Shell. Some 6,300 kilometres of 3-fold analogue seismic were acquired in 1961, and 3 wells were drilled during 1962 and 1963. In the same period, Kuwait Oil Company (KOC) also drilled their first 3 offshore exploration wells. In 1981, KOC embarked upon a second offshore exploration campaign, acquiring some 6,000 kilometres of seismic data and, during 1983 and 1984, drilling two wells. None of these wells was a commercial discovery.

Between 1995 and 1997, an integrated team of KOC and Shell explorers undertook a review of the hydrocarbon potential of Offshore Kuwait. In order to establish an integrated sequence-stratigraphical framework for the prospective Lower to Middle Cretaceous interval, a quantitative biostratigraphical study was made. Some 790 biostratigraphical analyses (10% core samples; 90% cuttings) from eleven wells were carried out: the nanno-fossil data was particularly important in providing accurate chronostratigraphical calibration, and this data has been used to constrain a “Time-Rock Synopsis”.

KOC’s lithostratigraphical nomenclature proved to be basically sound and has been maintained as the basis for the present stratigraphical framework. However, the study revealed the existence of two substantial and hitherto unsuspected hiati: one between the Ratawi and Zubair formations of Early Valanginian to Mid-Hauterivian age; and the other, representing the whole of the Early Albian, within the Burgan Formation. This latter result, if it can be further substantiated by more exhaustive study in the onshore area, would neccessitate a re-definition of the Burgan Formation and the erection of a new formation to describe the clastic sequence of Late Aptian age which lies between the Early Albian hiatus and the top of the Shu’aiba Formation, and which has hitherto been included within the Lower Burgan Formation.
Tectonic Evolution of Northeast Syria: Regional Implications and Hydrocarbon Prospects
Authors: Brew Graham , Litak Robert , Barazangi Muawia , Sawaf Tarif
Published: October 2021

We present the Phanerozoic tectonic evolution of northeast Syria and incorporate the results into regional deformation models of the northern Arabian Platform and nearby Arabian Plate boundaries. Based on analysis of extensive seismic reflection profiles and well data, we interpret that the Sinjar-Abd el Aziz area in northeast Syria was subsiding under extension at various rates from the Carboniferous until the end of the Mesozoic, most markedly during the latest Cretaceous. The predominant basin through most of the Late Paleozoic and Mesozoic was southwest-northeast trending; this formed the northeast extension of the major Palmyride Basin to the southwest. During the Late Cretaceous, extension in eastern Syria initiated along southeast-northwest and then east-west trends - possibly as a result of changing subduction geometries and plate motions in the Neo-Tethys to the northeast. The east-west striking faulting resulted in syntectonic deposition of up to approximately 1,600 meters of Late Campanian-Maastrichtian marly limestones in the Sinjar-Abd el Aziz area. The area was subjected to horizontal shortening throughout the Cenozoic, primarily during Plio-Pleistocene time, resulting in structural inversion along some of the faults. Although crustal shortening through the Syrian Sinjar and Abd el Aziz structures is relatively minor (approximately 1%), this has been critical to hydrocarbon trap formation in Mesozoic and Cenozoic strata through the formation of fault-propagation folds. We present regional models that show the interrelated tectonic history of northeast Syria, the Palmyrides, and the Euphrates Fault System are all inseparably linked to the polyphase opening and closing of the nearby Neo-Tethys Ocean.
Lithostratigraphy and Depositional History of Part of the Midyan Region, Northwestern Saudi Arabia
Authors: Hughes G. Wyn , Grainger David J. , Abu-Bshait Abdul-Jaleel , Abdul-Rahman M. Jarad
Published: October 2021

The Midyan region provides a unique opportunity in which to examine exposures of the Upper Cretaceous and Neogene sedimentary succession. Recent investigations have yielded new interpretations of its depositional environments, stratigraphic relationships, and structure. In this paper, all the lithostratigraphic units of the Midyan succession are considered to be informal in advance of an on-going process of formalization.

The region is bounded to the north and northeast by mountains of Proterozoic rocks and to the west and south by the Gulf of Aqaba and the Red Sea, respectively. The Wadi Ifal plain occupies most of the eastern half of the region, beneath which is a thick sedimentary succession within the Ifal basin. The oldest sedimentary rocks are the fluviatile Upper Cretaceous Adaffa formation and marine siliciclastics and carbonates of the lower Miocene Tayran group, unconformable on the Proterozoic basement. The Tayran group is unconformably overlain by the deep-marine lower Miocene Burqan formation that, in turn, is overlain by marine mudstones, carbonates, and evaporites of the middle Miocene Maqna group. The poorly exposed middle Miocene Mansiyah and middle to upper Miocene Ghawwas formations consist of marine evaporites and shallow to marginal marine sediments, respectively. The youngest rocks are alluvial sands and gravels of the Pliocene Lisan formation.

A complex structural history is due to Red Sea Oligocene-Miocene extension tectonics, and Pliocene-Recent anti-clockwise rotation of the Arabian Plate relative to Africa on the Dead Sea Transform Fault. The Upper Cretaceous succession is a probable pre-rift unit. The Oligocene?-Miocene syn-rift 1 phase of continental extension caused slow subsidence (Tayran group). Syn-rift 2 was an early Miocene phase of rapid subsidence (Burqan formation) whereas syn-rift 3 (early to middle Miocene) was another phase of slow deposition (Maqna group). The middle to late Miocene syn-rift 4 phase coincided with the deposition of the Mansiyah and Ghawwas formations. The Lower Pliocene to Recent succession is related to the drift (post-rift) phase during which about 45 kilometers of sinistral movement occurred on the Dead Sea Fault.

The structural control on sedimentation is evident: the Ifal basin was formed by east-west lithospheric extension; pull-apart basins occur along major left-lateral faults on the eastern coast of the Gulf of Aqaba; and basin-bounding faults controlled deposition of the Burqan, Ghawwas, and Lisan formations. Pliocene to Recent earth movements may be responsible for activating salt diapirism in the Ifal basin. Extensive Quaternary faulting and regional uplift caused the uplift of coral reefs to at least 6 to 8 meters above sea level.
Recognition and Interpretation of Polygenic Discontinuity Surfaces in the Middle Cretaceous Shu’aiba, Nahr Umr, and Natih Formations of Northern Oman
Authors: Immenhauser Adrian , Creusen Anouk , Esteban Mateu , Vonhof Hubert B.
Published: October 2021

Discontinuity surfaces that recorded superposition of marine hardground and subaerial exposure stages are common in the Middle Cretaceous of northern Oman. These surfaces formed during periods of rapid sea-level drop. The marine hardground stages are dominant in the field, whereas the subaerial exposure stage is documented in circumstantial petrographic, geochemical, and biological evidence. The record of a shoaling phase prior to exposure is commonly subtle and incomplete; supratidal deposits are conspicuously absent. Porosity in the limestones underlying the discontinuities is rearranged during subaerial exposure and subsequent burial and hence the permeability of large volumes of limestone is affected at a variety of scales. During marine hardground stages, carbonate cements, iron oxides, and manganese occludes some of the existing pore space. During burial, these intervals may thus have acted as either seals or efficient conduits of fluid flow. The surfaces under study in the Shu’aiba, Nahr Umr, and Natih formations are spaced ten to few tens of meters apart and many of them were traced laterally over distances of 100 kilometers and more between sections at Jebel Akhdar and in the Foothills. This implies that they play an important, but poorly understood role in compartmentalization of carbonate reservoir rocks.
A 9C-2D Land Seismic Experiment for Lithology Estimation of a Permian Clastic Reservoir
Authors: Macrides Costas G. , Kelamis Panos G.
Published: October 2021

In 1997, a nine-component shear wave experiment, the first of its kind in the country, was carried out in central Saudi Arabia over the Umm Jurf and Usaylah fields. The seismic source consisted of conventional and shear-wave vibrators. The objective of the experiment was to test the feasibility of using multicomponent seismic data for lithology estimation and differentiation between sand, silt and shale in the clastic Permian Unayzah Formation. The estimates of average ratios of compressional to shear-wave velocities for the target interval are encouraging as they identified lithologic variations within the Unayzah that are in agreement with the available well logs. Specifically, the seismic ratios correlate satisfactorily with sand/(silt+shale) ratios measured in key wells.
Origin of the Arabian Plate Structures: Amar Collision and Najd Rift
Authors: Al-Husseini Moujahed I.
Published: October 2021

The regularly spaced, N-trending Summan Platform, Khurais-Burgan Anticline, En Nala (Ghawar) Anticline and Qatar Arch in the eastern part of the Arabian Plate appear to have formed during the Precambrian Amar Collision between about 640 and 620 million years ago. This collision occurred along the N-trending Amar Suture (that bisects the Arabian Peninsula at about longitude 45 E) when the Rayn micro-plate in the east was fused to the western part of the Arabian Craton. The great anticlines are bounded by the NE-trending Wadi Batin Fault and NW-trending Abu Jifan Fault that converge on the Amar Suture. Deep wells drilled into these anticlines intersected deformed metasediments that are dated as syn-collisional. The Amar Collision was followed by a widespread extensional collapse of the Arabian-Nubian Shield between about 620 and 530 million years ago. During the final extensional stage, between about 570 and 530 million years ago, the NW-trending Najd Fault System dislocated the Arabian Shield left-laterally by about 250 to 300 kilometers. This dislocation appears to complement NE-oriented intra-continental rifts in Oman, Pakistan, Zagros Mountains and the Arabian Gulf. In these rift basins there accumulated thick sequences of clastic and carbonate rocks and salt, such as the Ara Group in Oman, Salt Range Formation in Pakistan, and Hormuz Series in the Arabian Gulf and Zagros Mountains. During the extensional collapse, the N-trending anticlines probably remained elevated as elongated horsts bounded by normal faults. The intervening subsiding grabens accumulated syn-rift sediments including the Hormuz Salt, and form an inter-fingering pattern between the great N-trending anticlines. The Precambrian anticlines, together with the syn-rift salt form the foundations of most of the hydrocarbon traps in the Arabian Plate.
Predictive Modelling of Naturally Fractured Reservoirs Using Geomechanics and Flow Simulation
Authors: Bourne Stephen J. , Rijkels Lex , Stephenson Ben J. , Willemse Emanuel J.M.
Published: October 2021

To optimise recovery in naturally fractured reservoirs, the field-scale distribution of fracture properties must be understood and quantified. We present a method to systematically predict the spatial distribution of natural fractures related to faulting and their effect on flow simulations. This approach yields field-scale models for the geometry and permeability of connected fracture networks. These are calibrated by geological, well test and field production data to constrain the distributions of fractures within the inter-well space. First, we calculate the stress distribution at the time of fracturing using the present-day structural reservoir geometry. This calculation is based on a geomechanical model of rock deformation that represents faults as frictionless surfaces within an isotropic homogeneous linear elastic medium. Second, the calculated stress field is used to govern the simulated growth of fracture networks. Finally, the fractures are upscaled dynamically by simulating flow through the discrete fracture network per grid block, enabling field-scale multi-phase reservoir simulation. Uncertainties associated with these predictions are considerably reduced as the model is constrained and validated by seismic, borehole, well test and production data. This approach is able to predict physically and geologically realistic fracture networks. Its successful application to outcrops and reservoirs demonstrates that there is a high degree of predictability in the properties of natural fracture networks. In cases of limited data, field-wide heterogeneity in fracture permeability can be modelled without the need for field-wide well coverage.
Tectonic and Geologic Evolution of Syria
Authors: Brew Graham , Barazangi Muawia , Al-Maleh Ahmad Khaled , Sawaf Tarif
Published: October 2021

Using extensive surface and subsurface data, we have synthesized the Phanerozoic tectonic and geologic evolution of Syria that has important implications for eastern Mediterranean tectonic studies and the strategies for hydrocarbon exploration. Syrian tectonic deformation is focused in four major zones that have been repeatedly reactivated throughout the Phanerozoic in response to movement on nearby plate boundaries. They are the Palmyride Mountains, the Euphrates Fault System, the Abd el Aziz-Sinjar uplifts, and the Dead Sea Fault System. The Palmyrides include the SW Palmyride fold and thrust belt and two inverted sub-basins that are now the Bilas and Bishri blocks. The Euphrates Fault System and Abd el Aziz-Sinjar grabens in eastern Syria are large extensional features with a more recent history of Neogene compression and partial inversion. The Dead Sea transform plate boundary cuts through western Syria and has associated pull-apart basins.

The geological history of Syria has been reconstructed by combining the interpreted geologic history of these zones with tectonic and lithostratigraphic analyses from the remainder of the country. Specific deformation episodes were penecontemporaneous with regional-scale plate-tectonic events. Following a relatively quiescent early Paleozoic shelf environment, the NE-trending Palmyride/Sinjar Trough formed across central Syria in response to regional compression followed by Permian-Triassic opening of the Neo-Tethys Ocean and the eastern Mediterranean. This continued with carbonate deposition in the Mesozoic. Late Cretaceous tectonism was dominated by extension in the Euphrates Fault System and Abd el Aziz-Sinjar Graben in eastern Syria associated with the closing of the Neo-Tethys. Repeated collisions along the northern Arabian margin from the Late Cretaceous to the Late Miocene caused platform-wide compression. This led to the structural inversion and horizontal shortening of the Palmyride Trough and Abd el Aziz-Sinjar Graben.
A crustal transect across the Oman Mountains on the eastern margin of Arabia
Authors: Al-Lazki Ali I. , Seber Dogan , Sandvol Eric , Barazangi Muawia
Published: October 2021

The unique tectonic setting of the Oman Mountains and the Semail Ophiolite, together with ongoing hydrocarbon exploration, have focused geological research on the sedimentary and ophiolite stratigraphy of Oman. However, there have been few investigations of the crustal-scale structure of the eastern Arabian continental margin. In order to rectify this omission, we made a 255-km-long, southwesterly oriented crustal transect of the Oman Mountains from the Coastal Zone to the interior Foreland via the 3,000-m-high Jebel Akhdar. The model for the upper 8 km of the crust was constrained using 152 km of 2-D seismic reflection profiles, 15 exploratory wells, and 1:100,000- to 1:250,000-scale geological maps. Receiver-function analysis of teleseismic earthquake waveform data from three temporary digital seismic stations gave the first reliable estimates of depth-to-Moho. Bouguer gravity modeling provided further evidence of depths to the Moho and metamorphic basement.

Four principal results were obtained from the transect. (1) An interpreted mountain root beneath Jebel Akhdar has a lateral extent of about 60 km along the transect. The depth-to-Moho of 41 to 44 km about 25 km southwest of Jebel Akhdar increased to 48 to 51 km on its northeastern side but decreased to 39 to 42 km beneath the coastal plain farther to the northeast. (2) The average depth to the metamorphic basement was inferred from Bouguer gravity modeling to be 9 km in the core of Jebel Akhdar and immediately to the southwest. A relatively shallow depth-to-basement of 7 to 8 km coincided with the Jebel Qusaybah anticline south of the Hamrat Ad Duru Range. (3) Based on surface, subsurface, and gravity modeling, the Nakhl Ophiolite block extends seaward for approximately 80 km from its most southerly outcrop. It has an average thickness of about 5 km, whereas ophiolite south of Jebel Akhdar is only 1 km thick. The underlying Hawasina Sediments are between 2 and 3 km thick in the Hamrat Ad Duru Zone, and 2 km thick in the Coastal Zone. (4) Southwest of Jebel Akhdar, reactivated NW-oriented strike-slip basement faults that deformed Miocene to Pliocene sediments were inferred from the interpretation of seismic reflection profiles.
Accurate reservoir characterization to reduce drilling risk in Khuff-C carbonate, Ghawar field, Saudi Arabia
Authors: Dasgupta Shiv N. , Hong Ming-Ren , Al-Jallal Ibrahim A.
Published: October 2021

The Khuff-C reservoir in the Ghawar field is a stratified sequence of cyclic carbonate-evaporite deposits within the Permian Khuff Formation. The reservoir is heterogeneous, complex, and influenced by syndepositional diagenesis. Wells drilled into the Khuff-C in the ‘Uthmaniyah sector of Ghawar are usually prolific producers of non-associated gas but some have intersected poor-quality reservoir intervals with little or no gas production. The Khuff-C reservoir rocks were deposited in a peritidal setting where slight changes in sea level created locally exposed highs. The exposure in an arid climate resulted in outliers of porosity occlusion formed by evaporite cements within the Khuff-C reservoir. The outliers are variably sized and randomly distributed and the challenge is to predict their occurrence in order to avoid them in development drilling. Inverse modeling of the ‘Uthmaniyah 3-D seismic data has identified the tight-porosity outliers as areas of anomalously high acoustic impedance. Integration of 3-D seismic analyses with petrophysical and other well data has improved the reservoir characterization and reduced the drilling risk.
A successful 3-D seismic survey over Bahrain Island
Authors: Postel Jean-Jacques , Mukhtar Abdul Nabi , Feugère Philippe
Published: October 2021

Environmental constraints are critical issues for land seismic operations and require the development of appropriate equipment and methods. In 1998, Compagnie Générale de Géophysique (CGG) acquired and processed seamless seismic data on behalf of the Bahrain Petroleum Company (Bapco) from a complex field on the Island of Bahrain. The operation ran smoothly in spite of the difficulty of working amongst pipelines, wells, and other oil and gas installations; scarps and sabkhas; urban areas; a zoo, golf course, and racecourse; an oil refinery and aluminum smelter; and other industrial and commercial facilities. The survey deployed a wide range of recording equipment including two sets of vibrators and a combination of radio and cable telemetry recording systems, and a fleet-management system.

The successful completion of the survey was achieved through dedicated teamwork. The key elements were as follows: (1) collecting the correct baseline information; (2) detailed planning of the timeframe, human and material resources, adaptation of acquisition techniques to varying circumstances, and health and safety requirements; (3) continuous monitoring of external conditions and the impact of the operation on the environment, in full consultation with the appropriate authorities; (4) maximum flexibility in the field operations so as to allow for changing conditions and unforeseen events; and (5) close partnership between CGG and Bapco at all stages of the project.

A joint CGG/Bapco team designed sophisticated processing methods, with top priority being given to the numerous surface heterogeneities. In particular, the recording of an intensive up-hole survey allowed a dedicated team at CGG in France to compute a robust subsurface model and a precise set of primary statics. Seven velocity layers from the Quaternary sandstone to the base of the calcareous and dolomitic Eocene were mapped. These showed significant lateral and vertical velocity variations within identified geological units. Surface-consistent signal processing with calibration to well data was used to compensate for the variations. Other critical processing steps included detailed velocity control, the application of dip moveout routines with acquisition-irregularity-compensation schemes, Radon demultiples and 3-D algorithms, designed for optimal de-noising and imaging.

These combined efforts led to the delivery of a final 3-D migrated block. As a result, a complete reinterpretation of the area was possible that significantly increased the estimated recoverable oil reserves (particularly by-passed oil) in the Awali field.
Structural setting and tectonic evolution of the Bahariya Depression, Western Desert, Egypt
Authors: Moustafa Adel R , Saoudi Ati , Moubasher Alaa , Ibrahim Ibrahim M , Molokhia Hesham , Schwartz Bernie
Published: October 2021

An integrated surface mapping and subsurface study of the Bahariya Depression aided the regional subsurface interpretation. It indicated that four major ENE-oriented structural belts overlie deep-seated faults in this part of the ‘tectonically stable’ area of Egypt. The rocks of the Bahariya area were deformed in the Late Cretaceous, post-Middle Eocene, and Middle Miocene-and subsurface data indicated an early Mesozoic phase of normal faulting. The Late Cretaceous and post-Middle Eocene deformations reactivated the early normal faults by oblique slip and formed a large swell in the Bahariya region. The crest was continuously eroded whereas its peripheries were onlapped by Maastrichtian and Tertiary sediments. The tectonic evolution of the Bahariya region shows great similarity to the deformation of the ‘tectonically unstable’ area of the northern Western Desert where several hydrocarbon fields have been discovered. This similarity may indicate that the same phases of deformation could extend to other basins lying in the ‘tectonically stable’ area, such as the Asyut, Dakhla, Nuqura, and El Misaha basins.
Lithological and structural evolution of the northern sector of Dukhan anticline, Qatar, during the early Tertiary: with special reference to sequence stratigraphic bounding surfaces
Authors: Dill Harald G. , Nasir Sobhi , Al-Saad Hamad
Published: October 2021

Early Tertiary sediments are widely exposed in Qatar and only in coastal areas and a few places inland do Holocene deposits mask them. The variable resistance to weathering of the Tertiary sediments is responsible for the general low-relief landscape interspersed with flat-topped hills, the most prominent of which are in western Qatar where they are the surface expression of the Dukhan anticline. The early Tertiary was a time of shallow-marine sedimentation and several transgressive and regressive cycles occurred. Sedimentation began on a dolomitic carbonate shelf, which gave way to a mixed carbonate-siliciclastic shelf that became increasingly calcitic. Coarsening-upward sequences with fine-grained muddy sediments at the base and grainstones and boundstones on top attested to a cyclic change in the energy regime. Small-scale cycles and major unconformities resulted from eustatic sea-level changes. In the Dukhan study area, the most prominent sequence boundary was near the Ypresian-Lutetian boundary. Following this hiatus, a Lutetian transgressive system tract evolved that was terminated by a maximum flooding surface correlated with the named MFS Pg20. Minor unconformities and NE-trending faults of post-Miocene age resulted from the interplay of local diapiric salt movements in the Dukhan anticline and a regionally changing stress field. Extensional faulting was succeeded by a compressional phase that caused the reactivation of some normal faults as steeply dipping reverse faults.

Diagenetic processes and the pervasive etching of the landscape formed ferrous, siliceous, and gypsiferous duricrusts. Phosphate was reworked and concentrated above the Ypresian-Lutetian unconformity. Ferricretes were derived from iron-bearing phyllosilicates and disulfides. Ferric iron-oxide hydrates were the result of oxidizing conditions but their parent material furnished evidence of less-oxygenated conditions and a rising sea level during the Lutetian transgression. The studies provided information on the economic potential of aggregates, clay, hydraulic binders, and building stones, and the prediction of subsidence-prone areas.
Lateral clay injection into normal faults
Authors: van der Zee Wouter , Urai Janos L. , Richard Pascal D.
Published: October 2021

The clay content of fault gouge is one of the main factors controlling transport and mechanical properties of a fault zone. This paper addresses the process of lateral clay injection into normal faults, which is one of the many processes contributing to the development of clay smear, and can lead to local enrichment of clay in a fault gouge. We combined field observations with geomechanical models to quantify the parameters leading to lateral clay injection into fault zones. Detailed field study shows that a releasing fault bend in a clay layer is required for clay injection to occur. The clay injection process is often associated with the formation of a branch in the fault and the development of a “squeezing block” which injects the clay into the fault zone. A simple analytical model predicts the onset of clay injection when C = σ'v (1 - sin ϕ) / (2 cos ϕ), where C is cohesion (MPa), σ'v is vertical stress (MPa) and ϕ (°) is friction angle. More detailed analysis using 2-D geomechanical finite element models is in good agreement with the analytical models and allows study of the system at higher fault throw. Results of sandbox models containing layers of an elastoplastic clay analogue also compare well with field observations and numerical models, and show the initiation of the releasing step and the evolution of the clay injection process with increasing fault throw. Using our results it is possible to predict the likelihood of lateral clay injection in the subsurface, in settings like the Gharif formation of the Haushi group of Central and South Oman or the Natih formation of North Oman. This requires an estimation of the mechanical properties of the clays at the time of faulting; data which can be obtained from wireline logs and cuttings. This approach to fault seal analysis emphasizes the mechanical aspects of the clay smear process, in addition to the kinematics which were considered in previous analyses. Its application should lead to improved prediction of fault seal processes in the subsurface.
Phanerozoic cycles of sea-level change on the Arabian Platform
Authors: Haq Bilal U. , Al-Qahtani Abdul Motaleb
Published: October 2021

The Arabian Plate has experienced a complex tectonic history while also being widely influenced by eustatic sea-level changes. These diastrophic events either affected changes in the rate and/or location of subsidence that in turn led to the creation of significant new sedimentary accommodation, or caused major erosional hiatuses. As a result, both eustasy and tectonics have played important roles in the development of sedimentary sequences and in determining the locus and characteristics of reservoir, source and seal facies on the Arabian Platform. Here, we present a synthesis (Cycle Chart) of the regional sea-level fluctuations affecting the Platform that is based on Phanerozoic epi- and peri-Platform sequence-stratigraphic data. Information used for the synthesis includes sections from Saudi Arabia, Kuwait, the Greater Gulf area, Oman and Yemen. The regional Cycle Chart incorporates interpreted sedimentary onlap patterns on the margins of the Arabian Platform, as well as models of regional sea-level fluctuations that controlled these patterns. These are compared to eustatic data that represents the ‘global-mean’ models of sea-level changes, largely at second-order cycle level for the Paleozoic and third-order cycle level for the Mesozoic and Cenozoic eras. The comparisons reveal that Phanerozoic sediment accumulation patterns on the Platform were broadly controlled by eustasy, with a strong overprint of tectonics for several long intervals. During periods of tectonic quiescence, however, correlations with the eustatic events improve significantly. Thus, for example, during the Cambrian through early Silurian and mid Jurassic through early Paleogene intervals eustasy may have been the significant controlling factor for sedimentary patterns when long-term trends in both regional and global sea-level curves show similarities.

The use of the Cycle Chart could facilitate exploration efforts on the Arabian Platform, provide better chronostratigraphic estimates and global correlations, and prove a useful accompaniment for sequence-stratigraphic studies. This integrative effort was greatly facilitated by the recent publication of the sequence stratigraphic synthesis of the Arabian Plate. The ages of Maximum Flooding Surfaces, however, have been recalibrated to the new (GTS 2004) time scale. This synthesis also represents a new recalibration of the Mesozoic and Cenozoic eustatic curves of Haq et al. (1988) to an up-to-date numerical time scale (GTS 2004).
Generation, migration, accumulation, and dissipation of oil in Northern Iraq
Authors: Dunnington H.V.
Published: October 2021

Most of the known oil accumulations of Northern Iraq probably originated by upward migration from earlier, deeper accumulations which were initially housed in stratigraphic or long-established structural traps, and which are now largely depleted. The earlier concentrations had their source in basinal sediments, into which the porous, primary-reservoir limestones pass at modest distances east of the present fields. Development of the region favored lateral migration from different basinal areas of Upper Jurassic and Lower-Middle Cretaceous time into different areas of primary accumulation.

Important factors affecting primary accumulation included: (1) early emergence and porosity improvement of the reservoir limestones, followed by burial under seal-capable sediments; (2) the timely imposition of heavy and increasing depositional loads on the source sediments, and the progressive marginward advance of such loads; (3) progressive steepening of gradients trending upward from source to accumulation area; (4) limitation of the reservoir formations on the up-dip margin by truncation or by porosity trap conditions. In late Tertiary time, large-scale folding caused adjustments within the primary reservoirs, and associated fracturing permitted eventual escape to higher limestone reservoirs, or to dissipation at surface.

The sulfurous, non-commercial crudes of Miocene and Upper Cretaceous reservoirs in the Qaiyarah area are thought to stem from basinal radiolarian Upper Jurassic sediments, which lie down dip, a few tens of miles east of these fields. Upper Cretaceous oils of Ain Zalah and Butmah drained upward from primary accumulations in Middle Cretaceous limestones, which were filled from basinal sediments of Lower Cretaceous age situated in a localized trough a few miles northeast of these structures. The huge Kirkuk accumulation, now housed in Eocene-Oligocene limestones, ascended from a precedent accumulation in porous Middle-Lower Cretaceous limestones, which drew its oil from globigerinal-radiolarian shales and limestones of the contemporaneous basin, a short distance east of the present field limits.

Eocene-Oligocene globigerinal sediments, considered by some the obvious source material for Kirkuk oil, seemingly provided little or no part of the present accumulation. The reservoir formation may have been filled from these sources, to lose its oil by surface dissipation during the erosional episode preceding Lower Fars deposition. Upper Cretaceous basinal sediments probably contributed nothing to known oil field accumulations, though they may have subscribed to the spectacular impregnations of some exposed, Upper Cretaceous reef-type limestones. Neither Miocene nor pre-Upper Jurassic sediments have played any discernible role in providing oil to any producing field. Indigenous oils are thought to be negligible in the limestone-reservoir formations considered.
Ostracods of the Permian-Triassic Khuff Formation, Saudi Arabia: palaeoecology and palaeobiogeography
Authors: Crasquin-Soleau Sylvie , Vaslet Denis , Le Nindre Yves-Michel
Published: October 2021

Ostracods were recovered for the first time from outcrops of the Permian-Triassic Khuff Formation in central Saudi Arabia. The fauna is exceptional in that the Khuff lithofacies were not considered favourable for their development and preservation. This ostracod fauna positions the Triassic-Permian Boundary between the Lower and Upper Khartam members of the Khuff Formation. The palaeoecological analysis shows that the Saudi Arabian Permian ostracods are typical of a shallow, intertropical, warm-water setting. The evolution of the ostracods is directly linked with variations of sea level, and particularly the two Late Permian maximum flooding events: (1) at the base of the Midhnab Member (MFI PKm), and (2) within the Lower Khartam Member (MFI PKk). Some of the species discovered in the Saudi Arabian outcrops are known from other countries. The provincialism index (PI) was used to establish the palaeobiogeographic relationships between different Palaeo-Tethyan areas. A schematic model of oceanic currents is proposed to explain the spreading of species.
Arabian Plate sequence stratigraphy: Potential implications for global chronostratigraphy
Authors: Simmons Michael D. , Sharland Peter R. , Casey David M. , Davies Roger B. , Sutcliffe Owen E.
Published: October 2021

The ability to recognise and correlate third-order depositional sequences across Arabia and between Arabia and other plates indicates that these sequences are driven by synchronous eustatic sea-level change. This is of value in providing guidance for the definitions of stages, which are the fundamental units of chronostratigraphy. Each Phanerozoic stage requires a Global Stratotype Section and Point (GSSP), which is a location and specific bedding plane where the base of each stage is defined. This definition is tied to an event in the rock record useful for correlation. Progress in defining GSSPs has been delayed because of difficulties in choosing the most appropriate event and section to relate to a definition. It is recommended here that stage boundaries be related to correlative conformities of sequence boundaries. This closely links chronostratigraphy with sequence stratigraphy and honours the original concepts upon which many stages were first described in the 19th Century.
Application of Thomeer Hyperbolas to decode the pore systems, facies and reservoir properties of the Upper Jurassic Arab D Limestone, Ghawar field, Saudi Arabia: A “Rosetta Stone” approach
Authors: Clerke Edward A. , Mueller Harry W. , Phillips Eugene Craig , Eyvazzadeh Ramsin Y. , Jones David H. , Ramamoorthy Raghu , Srivastava Ashok
Published: October 2021

We investigated the basic geological and petrophysical properties of the multimodal pore systems in the Arab D limestone facies in Ghawar field, Saudi Arabia. The study used more than 500 mercury injection capillary pressure (MICP) data, which were type-curve matched using Thomeer Hyperbolas. The new MICP sample data were drawn from 10 cored wells that transect the Ghawar field from north to south and from a previous fieldwide study with 125 MICP samples. These 500 samples have a very rich statistical foundation in that they were selected using only random decimation within each of the facies from more than 3,500 core plugs all with assigned facies. In addition to MICP data and facies, a former, smaller sample set had both facies and Dunham texture codes. A new view of these pore systems emerged, that is built upon the intrinsic, fundamental and separate maximum pore-throat diameter modal elements named porositons. Porositons are stable, recurring and intrinsic modes in the maximum pore-throat diameter of the carbonate pore systems. Analytical results derived from the MICP data showed that the pore systems of the Arab D limestones can be classified based on porositons. The benefits of this new classification are demonstrated by considering in detail the relationships to geological facies, well-log responses, permeability modeling and simple nuclear magnetic resonance (NMR) well-log response. By analogy to the decoding of the Egyptian hieroglyphics using the Rosetta Stone, the use of porositons enables strong connections to be made between the geological facies, petrophysical and reservoir-flow properties of these complex carbonate rocks. The relationships between the new pore systems categories and the facies were thoroughly tested using north-south field trends.