bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impact of basin evolution, depositional environment, pore water evolution and diagenesis on reservoir-quality of Lower Paleozoic Haima Supergroup sandstones, Sultanate of Oman
Authors: Ramseyer Karl , Amthor Joachim E. , Spötl Christoph , Terken Jos M.J. , Matter Albert , Hove Marietta Vroon-ten , Borgomano Jean R.F. 
Published: October 2021

ABSTRACTSandstones of the Early Paleozoic Miqrat Formation and Barik Sandstone Member (Haima Supergroup) are the most prolific gas/condensate containing units in the northern part of the Interior Oman Sedimentary Basin (IOSB). The reservoir-quality of these sandstones, buried to depths exceeding 5 km, is critically related to the depositional environment, burial-related diagenetic reactions, the timing of liquid hydrocarbon charge and the replacement of liquid hydrocarbon by gas/condensate.The depositional environment of the sandstones controls the net-sand distribution which results in poorer reservoir properties northwards parallel to the axis of the Ghaba Salt Basin. The sandy delta deposits of the Barik Sandstone Member have a complex diagenetic history, with early dolomite cementation, followed by compaction, chlorite formation, hydrocarbon charge, quartz and anhydrite precipitation and the formation of pore-filling and pore-lining bitumen. In the Miqrat Formation sandstone, which is comprised of inland sabkha deposits, similar authigenic minerals occur, but with higher abundances of dolomite and anhydrite, and less quartz cement. The deduced pore water evolution from deposition to recent, in both the Miqrat Formation and the Barik Sandstone Member, reflects an early addition of saline continental waters and hydrocarbon-burial related mineral reactions with the likely influx of lower-saline waters during the obduction of the Oman Mountains.Four structural provinces are recognized in the IOSB based on regional differences in the subsidence/uplift history: the Eastern Flank, the Ghaba and Fahud Salt Basins and the Mabrouk-Makarem High. In the Fahud Salt Basin, biodegradation of an early oil charge during Late Paleozoic uplift resulted in reservoir-quality degradation by bitumen clogging of the pore space. On the Eastern Flank and the Mabrouk-Makarem High, however, the early oil bypassed the area. In contrast, post-Carboniferous liquid hydrocarbons were trapped in the Mabrouk-Makarem High, whereas on the Eastern Flank surface water infiltration and loss of hydrocarbons or biodegradation to pore occluding bitumen occurred. In the Ghaba Salt Basin, post-Carboniferous hydrocarbon charge induced a redox reaction to form porosity/permeability preserving chlorite in the reservoirs. The liquid hydrocarbons were replaced since the obduction of the Oman Mountains by gas/condensate which prevented the deep parts (&gt;5,000 m) of the Ghaba Salt Basin from pore occluding pyrobitumen and thus deterioration of the reservoir quality.
Seismic forward model of a Natih Formation outcrop: the Adam Foothills Transect (northern Oman)
Authors: Anne M.Schwab , Peter W.Homewood , Frans S.P.van Buchem , Philippe Razin 
Published: October 2021

ABSTRACT
The platform carbonates of the Natih Formation (Albian-Turonian) are hydrocarbon reservoirs throughout the Middle East. This study uses a high-resolution sequence stratigraphic model built from the Natih outcrops of the Adam Foothills Transect, in northern Oman, as the basis for the construction of synthetic seismic sections along the Natih outcrops. The model covers the seaward progression from a proximal carbonate platform to a distal intrashelf basin. Three third-order depositional sequences had been identified and correlated across the outcrops, and facies were mini-core plugged for petrophysical data measurement, which were then used to construct an impedance model from the stratigraphic model. This impedance model was used to construct synthetic seismic sections with a zero phase Ricker wavelet at varying peak frequencies (80 Hz, 60 Hz and 40 Hz). The high-frequency synthetic seismic identified seismic characteristics of specific depositional environments, notably the organic-rich intrashelf basin, the platform margin and the platform interior. These seismic characteristics were very subtle on the lower frequency data, but could nonetheless be identified. A seismic line passing through a nearly analogous setting in the subsurface Natih was used to try and identify the characteristics observed on the synthetic seismic data. Many of the synthetically-produced characteristics were found on the industry seismic, which shows that this method is a good way of using the detail of the outcrop to help with predictions on the lower frequency/resolution seismic.
Correlation of the Lower Permian surface Saiwan Formation and subsurface Haushi limestone, Central Oman
Authors: Angiolini Lucia , Stephenson Michael H. , Leven Ernst J. 
Published: October 2021

ABSTRACT
The palaeontology of the Saiwan Formation (Lower Permian) of the Al-Huqf outcrop area, Central Oman, has been the subject of significant study, but that of approximately equivalent beds in the subsurface (the Haushi limestone and ‘basal sandstones’ of the lower Gharif member) has been unknown until now. This has meant that the precise relationship between the surface and subsurface units has been poorly understood. A new subsurface brachiopod study has allowed a fourfold biozonation that correlates the surface Saiwan Formation with the subsurface Haushi limestone, implying that previous direct correlation of the Saiwan Formation with the lower Gharif member is not correct. Overall the brachiopod fauna of the subsurface is of lower diversity than that of the outcropping Saiwan Formation, suggesting deposition in quieter and deeper marine settings. The occurrence of a fusulinid assemblage with Pseudofusulina ex gr. karapetovi karapetovi Leven, the first such record in Gondwana, suggests a Sakmarian age for the Haushi limestone, and brachiopod data supports this determination. Subsurface Haushi limestone palynological assemblages, though diverse, are poorly preserved, and no palynomorphs have been recovered from equivalent surface outcrops. However, the distribution of autochthonous algal spores in three of the subsurface Haushi limestone sections suggest a local biozonation that is consistent with that indicated by brachiopods, while the terrestrially-sourced palynomorphs in the subsurface Haushi limestone sections indicate an OSPZ3c age. Surprisingly the sections contain no palynomorphs of unequivoval marine origin. Fusulinids indicate that a Sakmarian age for OSPZ3c is more likely than the Artinskian age suggested by previous palynological studies. The terrestrially sourced palynomorphs also suggest correlation of the carbonates of the Haushi limestone with the highest part of the clastic lower Gharif Member in South Oman, above the Ulanisphaeridium omanensis Biozone or Maximum Flooding Shale in that area. Using the new biozonation, the distribution of facies has been mapped for three time slices. This reveals an increase in carbonate deposition during the Sakmarian due to distancing and deepening of the terrigenous source, coupled with climatic warming, culminating with a regressive trend at the end of the cycle. A progressive increase in carbonate deposition is recorded westward into the basin.
Late Cretaceous to Paleogene post-obduction extension and subsequent Neogene compression in the Oman Mountains
Authors: Fournier Marc , Lepvrier Claude , Razin Philippe , Jolivet Laurent 
Published: October 2021

ABSTRACT
After the obduction of the Semail ophiolitic nappe onto the Arabian Platform in the Late Cretaceous, north Oman underwent several phases of extension before being affected by compression in the framework of the Arabia-Eurasia convergence. A tectonic survey, based on structural analysis of fault-slip data in the post-nappe units of the Oman Mountains, allowed us to identify major events of the Late Cretaceous and Cenozoic tectonic history of northern Oman. An early ENE-WSW extensional phase is indicated by synsedimentary normal faults in the Upper Cretaceous to lower Eocene formations. This extensional phase, which immediately followed ductile extension and exhumation of high-pressure rocks in the Saih Hatat region of the Oman Mountains, is associated with large-scale normal faulting in the northeast Oman margin and the development of the Abat Basin. A second extensional phase, recorded in lower Oligocene formations and only documented by minor structures, is characterized by NNE (N20°E) and NW (N150°E) oriented extensions. It is interpreted as the far-field effect of the Oligocene-Miocene rifting in the Gulf of Aden. A late E-W to NE-SW directed compressional phase started in the late Oligocene or early Miocene, shortly after the collision in the Zagros Mountains. It is attested by folding, and strike-slip and reverse faulting in the Cenozoic series. The direction of compression changed from ENE-WSW in the Early Miocene to almost N-S in the Pliocene.
Megaseismic section across the northeastern slope of the Arabian Plate, Iraq
Authors: Mohammed Sabah A.G 
Published: October 2021

ABSTRACTA composite seismic image (Megaseismic Line 7) was constructed across Iraq using 16 pre-existing seismic lines that were recorded between 1975 and 1983. The image is the first of 15 megaseismic lines that will eventually form a rectilinear grid that covers Iraq. It is oriented in a SW-NE direction, and extends approximately 500 kilometers from the Iraq-Saudi Arabia border to the Iraq-Iran border. The seismic lines were recorded using a 48-channel system with either a vibroseis or dynamite source. The maximum offset varies from 2,400 to 5,000 meters. The seismic data was reprocessed using a common datum of 300 meters above sea level. Data quality is good where the source was dynamite and the terrain consists of gravel and sand surfaces; it is poor where vibroseis was used or/and the outcrops were carbonates. The final stacked section and Hilbert attributes (reflection amplitude and instantaneous phase) were displayed at different scales to determine the best perspective for interpretation. A total of 14 reflections, corresponding to Miocene to Permian horizons, were identified using synthetic seismograms from five wells. The horizons generally dip towards the northeast, except at the location of the Tel Ghazal oil field where syndepositional growth is inferred. Various seismic stratigraphic geometries, such as sigmoidal features, onlap, toplap and downlap, were identified and used to define disconformities and angular unconformities.The oldest two horizons that could be picked are from the tops of the Triassic Kurra Chine and Permian Chia Zairi formations. Below the oldest Permian reflection, the middle Carboniferous “Hercynian unconformity” was tentatively picked. The Paleozoic pre-Permian succession is not adequately imaged in the seismic data, nor is the crystalline basement seen. The seismic interpretation was compared to the profiles of the Bouguer gravity anomaly and the total magnetic field, and good correlations were established. The regional line helped identify several previously unknown structural features including the Ma’aniya Depression in the Western Desert, and two anticlinal structures: the first being within that depression and the second directly to the southwest of Tel Ghazal oil field.
Fault growth and coalescence: insights from numerical modelling and sandbox experiments
Authors: Filbrandt Jacek B. , Richard Pascal D. , Franssen Raymond 
Published: October 2021

ABSTRACT
Displacement of strata varies along the strike of faults. This has important implications for the hydrocarbon industry, since for example this affects the occurrence and distribution of fractures along faults in a reservoir and can influence the sealing capacity of faults. As faults grow, neighbouring faults will interact with each other and eventually connect or coalesce. Geometrical fault growth models for coalescence are used to explain a large part of the observed spread of one order of magnitude in Length and Maximum Throw in natural examples of fault populations. Numerical modelling indicates that coalesced (merged) faults tend to return to their steady state growth evolution by accumulating displacement more rapidly than increasing in length, if no further coalescence occurs. Therefore, repetitive coalescence leaves faults “under-displaced” and results in a considerable spread in Length and Maximum Throw. To confirm and support these observations, a series of sandbox experiments was performed, which help improve our understanding of fault growth processes. The fault geometries observed in these models reflect geometries in natural examples, for example in the Natih Formation of Al Jabal al Akhdar in Oman. With increasing strain, repetitive coalescence takes place at all scales. After linkage, a new, coalesced fault behaves as a single, linked segment and accumulates more displacement than increasing length during an increment of strain. The slope of the best fit line of Length vs. Maximum Throw data for the fault population, in double logarithmic space, steepens with increasing strain and stabilises at about one.
Methanogenesis during Shu’aiba diagenesis: examples from Al Shaheen Field, Block 5, offshore Qatar
Authors: Raven Madeleine J. , Dickson Tony 
Published: October 2021

ABSTRACT
Evidence has been found for the involvement of bacterial methanogenic processes in the diagenesis of late Early Aptian Shu’aiba Formation sedimentary rocks from Block 5, offshore Qatar. This is in the form of δ13C values significantly higher than the presumed late Early Aptian marine signal. High δ13C values were recorded in early-formed inclusion-rich calcite that represents neomorphosed aragonite/marine cement (+6.6‰) and the latest precipitated blocky non-ferroan calcite cement (+8.9‰). Oxygen-isotope data suggest that the later methanogenic episode occurred during burial. In bulk rock samples from another well, δ13C values of +6.5 to +11.5‰ were determined from a 10 ft thick zone located 4 ft below the top of the Shu’aiba. In other wells for which data were available the equivalent interval of the Shu’aiba was characterised by expected marine δ13C values. Finally, δ13C values up to +9.1‰ were recorded in a localised area of dolomite replacement immediately beneath the Top Shu’aiba surface, which can be dated to after the onset of Nahr Umr Formation deposition. These are the first reported examples of methanogenic reactions affecting the Shu’aiba Formation and provide new insight into the diagenesis of this formation, which is often assumed to be dominated by meteoric processes. The evidence presented for the resetting of the carbon-isotope composition of the bulk rock has implications for the application of carbon-isotope stratigraphy to the Shu’aiba Formation.
Controls on diagenesis of the Triassic Kurrachine Dolomite, Syria
Authors: Hips Kinga , Árgyelán Gizella B. 
Published: October 2021

ABSTRACT
The evaluation of major diagenetic processes affecting the main hydrocarbon-producing interval of the Triassic Kurrachine Dolomite, in the central part of Syria, has proved to be of importance in understanding its reservoir characteristics. To describe the paragenetic sequence, core samples from two wells were studied by conventional petrographic analysis. In the first stage, pervasive replacement dolomitisation occurred. The dolomite petrography can be best explained by evaporative dolomitisation in the case of tidal flat facies and by the hypersaline brine reflux model in the case of subtidal facies. During relatively longer periods of subaerial exposure dolocrete sequences were developed. Dolomitisation of subtidal sediments in a more open-marine setting was completed during further burial by rising temperature. As a result, pervasively dolomitised rocks, with minor intercrystalline porosity in subtidal deposits and supposedly in dolocretes, were formed. In the deep burial realm, solution seams and stylolites acted as conduits for migrating hydrocarbon. Overmature hydrocarbon was observed as insoluble residue. Following fracturing and leaching by sulphate-bearing warm fluids, significant vuggy porosity was created but was subsequently occluded by precipitated anhydrite cement. The effective vuggy and fracture porosity of the Kurrachine Dolomite was created by latest stage leaching, which was controlled by the previous deep burial diagenetic processes and fracturing. The selective leaching, on the evidence of dissolution of anhydrite cement, improved the reservoir potential. Taken all together, the Kurrachine Dolomite exhibits evidence of important porosity development in burial conditions. Accordingly, the analysed core porosity and permeability data within the formation varies by location.
Characterization and significance of dedolomite in Wadi Nisah, central Saudi Arabia
Authors: Cantrell Dave L. , Al-Khammash Abdullah , Jenden Peter D. 
Published: October 2021

ABSTRACT
Two different types of calcified dolomite, or dedolomite, occur as stratiform and non-stratiform bodies within the Jurassic (Kimmeridgian) upper Jubaila Formation in the Wadi Nisah area of central Saudi Arabia. In the stratigraphically-equivalent subsurface Arab-D reservoir in eastern Saudi Arabia, two types of dolomite, stratiform and non-stratiform, occur which appear to be similar in architecture to the dedolomites examined in this study. However, Wadi Nisah dedolomites exhibit systematic changes in texture and isotopic composition from their precursor dolomites. Non-stratiform dedolomite contains lower oxygen isotope (average δ18O = -10.99‰) and much lower carbon isotope (average δ13C = -7.51‰) values and is much more coarsely crystalline than typical subsurface Arab-D non-stratiform dolomite; in contrast, Wadi Nisah stratiform dedolomite contains similar oxygen isotope values (δ18O = -2.89‰) and only slightly lower carbon isotopes (δ13C = 0.98‰) relative to subsurface Arab-D stratiform dolomites. We suggest that non-stratiform dolomite was more susceptible to late meteoric diagenesis than the horizontally bedded stratiform dolomite intervals. Such differences in character highlight the importance of structural and diagenetic architecture in determining later, post-dolomitization diagenesis and ultimately final reservoir quality.
High-resolution seismic imaging of a deep gas reservoir from azimuthal offset VSP, Saudi Arabia
Authors: Owusu John C. , Nebrija Edgardo L. 
Published: October 2021

ABSTRACT
A multi-offset, azimuthal, three-component VSP survey was acquired over a deep Unayzah sandstone gas reservoir in central Saudi Arabia. The objective was to confirm the direction for a proposed horizontal sidetrack to a vertical delineation well. A production test at the vertical well indicated a possible reservoir boundary less than 100 feet away from the well. It was hoped that some of the offset sections might image a small fault, which may represent such a boundary. In addition to the normal zero-offset VSP conducted at the vertical well, two multi-offset VSPs at orthogonal azimuths, and four single-offset VSPs at other azimuths were acquired.
Due to excellent cased-hole conditions for the receivers and uniform sandy terrain for the sources, the VSP records were nearly noise-free. The VSP data had virtually twice the dominant frequency of the surface seismic data. The offset VSP sections (both compressional and shear) succeeded in better resolving the reservoir properties of the gas-bearing Unayzah-A sandstone. They showed that its quality deteriorates to the northeast, whereas both its thickness and porosity remain uniform to the northwest, the proposed direction of the horizontal sidetrack. The shorter offset sections in each quadrant surrounding the well showed no clear disruptions that may indicate faulting. This suggests that the boundary detected from the well test may be due to facies change, cementation, or mineralized fractures associated with a major fault bounding the accumulation to the south.
The Middle Miocene Fatha (Lower Fars) Formation, Iraq
Authors: Al-Juboury Ali Ismail , McCann Tom 
Published: October 2021

ABSTRACT
The Middle Miocene Fatha Formation (previously Lower Fars Formation) in northern Iraq was deposited in a broad and shallow foreland basin adjacent to the Zagros and Taurus Mountains. It forms a transgressive-regressive sequence comprising numerous shallowing-upward cycles of alternating mudrocks, limestones, gypsum and/or anhydrite and halite. These cycles reflect rapid changes in accommodation space in settings that ranged from open and restricted hypersaline marine to continental (sabkha and fluvio-deltaic). In the marginal parts of the basin, continental siliciclastics (red and variegated marls, silts and fine sandstones) represent either aeolian deposition or a combined lagoonal- and/or fluvial-dominated delta system. Eustasy, rather than tectonics, caused the high-frequency cyclicity seen in the Fatha Formation. We present twelve sections dominated by evaporites from the Sinjar and Fatha sub-basins to represent the main lithologic constituents of the formation. Our detailed analysis of the sedimentary succession focuses on the three main lithofacies (siliciclastics, carbonates and evaporites). Petrographic, geochemical and scanning electron microscope analysis of these units are presented. We identified a range of carbonate lithotypes: marly, arenaceous (detrital), organic-rich (fossiliferous), dolomitic limestone and dolomite. Dolomitic limestones occur mostly in the lower part of the lower member of the formation, which was deposited in a barred lagoonal environment with high salinity. The presence of peloidal lime-wackestone with bioclasts, particularly in the upper part of the lower member of the formation, may reflect quiet, shallow-water marine conditions with moderate depths and low energy. The bioclastic-peloidal grainstone-packstone microfacies, with a common and diverse fossil assemblage, may reflect high to moderate energy, shallow-water environments. Evaporites comprise the main sediments of the Fatha Formation. Nodular gypsum is the dominant gypsum type, although laminated, thick-bedded, and secondary gypsum (selenite and satin spar) also occur. In the subsurface, anhydrite and halite are the principal minerals.
Constraints on the diagenesis, stratigraphy and internal dynamics of the surface-piercing salt domes in the Ghaba Salt Basin (Oman): A comparison to the Ara Group in the South Oman Salt Basin
Authors: Reuning Lars , Johannes Schoenherr , Ansgar Heimann , Urai Janos L. , Littke Ralf , Kukla Peter A. , Rawahi Zuwena 
Published: October 2021

ABSTRACT
In the South Oman Salt Basin (SOSB), the Ara carbonates form an extensively cored, deeply buried intra-salt hydrocarbon play. Six surface-piercing salt domes in the Ghaba Salt Basin (northern Oman) provide the only outcrop equivalents for carbonates and evaporites of the Ediacaran – Early Cambrian Ara Group (upper Huqf Supergroup). Based on fieldwork, satellite images and isotope analysis it is concluded that most of the carbonate bodies (so-called stringers) in the Ghaba salt domes are time-equivalent to the stratigraphically uppermost stringer intervals in the SOSB (A5–A6). Maturity analyses demonstrate that the carbonate stringers in the salt domes were transported with the rising Ara Salt from burial depths of c. 6 to 10 km to the surface. Petrographic and stable-isotope data show that their diagenetic evolution during shallow and deep burial was very similar to the Ara carbonate stringer play in the SOSB. However, during the retrograde pathway of salt diapir evolution, the carbonate stringers were exposed to strong deformation in the diapir stem and diagenetic alterations related to dedolomitisation. As the salt domes contain facies that are in all aspects identical to the deeply buried Ara play in the SOSB, this study provides substantial additional information for hydrocarbon exploration in southern Oman. Moreover, our work has implications for the hydrocarbon prospectivity of the Ghaba Salt Basin and possibly of other Ediacaran – Lower Cambrian evaporite basins in the Middle East, such as for the time-equivalent Hormuz salt basins.