bluuebunny/crossref_metadata_2025_split huggingface dataset:
Combining high-resolution sequence stratigraphy and mechanical stratigraphy for improved reservoir characterisation in the Fahud field of Oman
Authors: Morettini Elena , Thompson Anthony , Eberli Gregor , Rawnsley Keith , Roeterdink Roeland , Asyee Wenche , Christman Peter , Cortis Anthony , Foster Karen , Hitchings Victor , Kolkman Wilhelm , van Konijnenburg Jan-Henk 
Published: October 2021

ABSTRACT
In the Fahud field of Oman, the integration between hierarchies of sequence stratigraphic units and fracture systems has proven to be crucial to explain the distribution of flow and mechanical units. The study focused on the Upper Cretaceous, Albian to Lower Cenomanian Natih e unit (Natih Formation, Wasia Group), a 170-mthick carbonate sequence/reservoir, which exhibits heterogeneities in both facies and reservoir quality. Based on a core-derived high-resolution sequence stratigraphic analysis, the Natih e reservoir can be subdivided into four orders of depositional cycles (from 6th- to 3rd-order). Each cycle consists of a transgressive and regressive hemicycle with characteristic facies and rock properties. The facies and diagenetic overprint of the higher-order cycles vary according to their position within the 3rd-order sequences. Analysis of core, borehole images, seismic, tracer and production data indicate a hierarchy of fractures and faults that seems to follow the stratigraphic subdivisions. A relationship between depositional and diagenetic architecture of the cycles, and the aforementioned data, led to the identification of mechanical layering and stratigraphy within the reservoir. This finding was validated and supported by the successful history match of the three-phase production data within the dynamic model of the reservoir. The combination of sequence and mechanical stratigraphy provides a framework for the correlation of facies and mechanical units across the field. Furthermore, the facies and mechanical units are related to reservoir quality and fracture distribution for consistent upscaling into large-scale reservoir models. Through close co-operation between geologists and reservoir engineers utilising dynamic data, it was possible to determine the most appropriate scale for flow and ensure that such a scale was then used as input for dynamic modelling and for planning of the future exploitation of the Fahud field. As a result of this study, Petroleum Development Oman (PDO) has evaluated a 20% increase in risked reserves, and a 25% reduction of well costs.
Nautiloids of the Permian-Triassic Khuff Formation, central Saudi Arabia
Authors: Chirat Régis , Vaslet Denis , Le Nindre Yves-Michel 
Published: October 2021

ABSTRACT
Nautiloids are described for the first time from the outcrops of the lower part of the Midhnab Member and the lower part of the Khartam Member of the Khuff Formation in central Saudi Arabia. The nautiloids from the lower Midhnab Member, including Tirolonautilus gr. hoernesi, were found at two localities, and are associated with conical shaped cephalopodes (bactritids), bivalves, brachiopods, foraminifers, algae and ostracods. The nautiloids were recovered from the most marine horizon of the Khuff Formation. The nautiloid fauna confirms the Late Permian (Changhsingian) age assigned to the Midhnab Member based on the foraminiferal assemblage. In the lower part of the Khartam Member, a single specimen of Tirolonautilus feltgeni n. sp. is described here. It occurs in association with other cephalopods (bactritids), bivalves, foraminifers, and ostracods. The specimen confirms the Late Permian age (late Changhsingian) assigned to the Lower Khartam Member based on foraminiferal and ostracod assemblages. This marine fauna is located within the latest Permian maximum flooding event of central Saudi Arabia. The Khuff Formation nautiloids are compared to other fauna in the Peri-Tethys, particularly the southern Alps, where similar forms are described. Their similarity confirms a Late Permian marine exchange between the Arabian platform and the Western Tethyan realm.
Pre-stack 3-D Tau migration and velocity analysis: application to 3-D seismic data from offshore Abu Dhabi, United Arab Emirates
Authors: Alkhalifah Tariq , Al Sharif Saif , Belaid Kamal 
Published: October 2021

ABSTRACT
A pre-stack 3-D Tau migration was applied to a 3-D seismic data set acquired in offshore Abu Dhabi, United Arab Emirates. The velocity model was built through an initial series of 2-D Tau migration velocity analysis, and supplemented by 3-D subset migration. A 3-D Tau migration velocity analysis was used for the final two updates of the model. The final interval velocity model provided low residuals in the common-image gathers from different offsets and was consistent with velocities from four wells located in the region. This velocity model included the main known features of the region including a low-velocity zone and a major fault. A final 3-D pre-stack Tau migration was applied using the velocity model and a relatively moderate aperture. This migration imaged the region including part of the critical poor data quality region, which includes the reservoir as well as reflections from the fault. Based on the derived velocity model, we concluded that the major cause for the poor image is the presence of a shallow high-velocity anomaly separated by a fault from a low-velocity anomaly.
Key elements to clarify the 110 million year hiatus in the Mesozoic of eastern Syria
Authors: Caron Cécile , Mouty Mikhail 
Published: October 2021

ABSTRACT
Log correlations, biostratigraphical results and seismic data were combined to show that from Late Triassic Norian to Early Cretaceous Aptian times, the Euphrates area (Eastern Syria) was part of a huge saddle-like northeast-trending ridge (the Hamad Uplift) characterized by a prolonged stratigraphic hiatus. This uplift, developed in the Late Triassic, was multiply reactivated during the Mesozoic, particularly in the Early Cretaceous Aptian-Albian times, during a major reorganization phase of the Neo-Tethyan rift system. This uplift marked the separation between two regions with distinctive tectono-sedimentary evolutions: an eastern isolated and starved region (Euphrates Graben) and a western region that was mainly influenced by the sedimentary dynamics of the westerly Bishri Trough, linked to the Palmyrides Basin. The Hamad Uplift broke-up into a N140°E-oriented graben system in late Albian times. This early NE-trending extensional stage was accompanied by volcanic activity and introduced the main phase of horst-and-graben development within the Euphrates Graben in the Late Cretaceous Senonian times.
Lithology estimation from a multicomponent 3D-4C OBC seismic survey over a clastic reservoir in the Arabian Gulf
Authors: Macrides Costas G. , Neves Fernando A. 
Published: October 2021

ABSTRACT
In 2002, Saudi Aramco conducted its first 3D, 4-component (4C) ocean-bottom cable (OBC) seismic survey in the Arabian Gulf. The main objective was to delineate the middle Cretaceous Upper Khafji Sand Stringers Reservoir overlying the massive Main Khafji Sand Reservoir in the Zuluf field. The Upper Khafji Sand Stringers Reservoir in the Wasia Formation is typically characterized by weak acoustic impedance contrasts. A pre-survey modeling study, based on the logs of compressional (P) and shear-wave (S) velocities (Vp and Vs), indicated that converted compressional-to-shear waves (P-S) could better-image the structure and stratigraphy of the target reservoir. Commensurate with the objectives of the experiment, a pilot 100-square-kilometer survey was acquired with an inline swath-shooting geometry that employed two seabed receiver cables, with a symmetric split-spread deployment of the 4-C sensors. The acquisition geometry consisted of six sail lines per swath with a single-boat, dual-source, flip-flop configuration.
The data were processed through dual-sensor summation, horizontal-component rotation and P-P/P-S pre-stack time migration. Post-stack enhancement using non-stationary Gabor deconvolution proved beneficial in compensating for the missing high frequencies in the acquired converted-wave data. Well-to-seismic calibration for both P-P and P-S data at five wells aided in the interpretation of the data. Five horizons were interpreted and correlated between the P-P and P-S sections. The horizons were analyzed using both amplitude and interval times such that the lateral variations of the Vp/Vs ratio of the Upper Khafji Sand Stringers Reservoir could be mapped. A region of low Vp/Vs ratios in the northwest quadrant, obtained from the isochron interval-time analysis, was correlated with higher ‘net sand’ pay at a hidden well located in the middle of this region. These results were further corroborated by seismic facies analysis and provide a qualitative reservoir quality index in the Upper Khafji Sand Stringers Reservoir.
Correlation of the Al Khlata Formation in the Mukhaizna field, Oman, based on a new downhole, cuttings-based palynostratigraphic biozonation
Authors: Stephenson Mike H. , Al Rawahi Asya , Casey Brian 
Published: October 2021

ABSTRACT
Palynology is the primary method of correlating the subsurface glaciogenic Al Khlata Formation of Oman, due to extreme lateral variability of lithofacies, and poor seismic resolution. Up to now, however, it has been difficult to use cuttings samples because published and in-house palynological zonations rely mainly on quantitative variations in palynomorph groups, and such samples are susceptible to downhole caving. Study of around 400 samples from 12 well sections in the Mukhaizna field in south-central Oman has revealed a small number of palynomorphs that can be used alongside quantitative assemblage character to distinguish five biozones. The biozones are defined downhole using mainly cuttings samples. The top of the highest, Biozone A, is marked by the first downhole increase of Microbaculispora tentula and Cycadopites cymbatus and is associated with high gamma-ray readings indicating the Rahab Member of the Al Khlata Formation. Its quantitative character is similar to the upper parts of Oman and Saudi Arabia Palynological Zone 2 (OSPZ2) as well as the Converrucosisporites confluens Zone of the Collie Basin, Western Australia, and is therefore Sakmarian (Early Permian) in age. The top of Biozone B is distinguished by the first downhole appearance (FDA) of common cavate-zonate spores, and Densoisporites truswellii sp. nov., and is also likely to be Sakmarian in age. It is associated with shaley diamictites and more distal lacustrine mudstones with considerable lateral variability. The top of Biozone C is marked by the FDA of Anapiculatisporites concinnus but also contains persistent occurrences of Ahrensisporites cristatus, Spelaeotriletes triangulus and Deusilites tentus and is similar to Stage 2 of the Collie Basin and is therefore likely to be Asselian (earliest Permian) in age. It is associated with thick sequences of shaley diamictites that occur throughout the Mukhaizna field with relatively little lateral variability, suggesting very long-lived, large, proglacial or subglacial lakes. A lower subdivision of Biozone C, termed Sub-Biozone C1 is distinguished by very high percentages of cavate-zonate spores. Biozone D, of probable Carboniferous age, is characterised by dominant monosaccate pollen and Punctatisporites, contains small numbers of distinctive spores such as Indotriradites fibrosus sp. nov. and Auroraspora sp. A, and is associated with thick, stacked sandstone sequences and sandy diamictites with extremely high lateral variability. The thickness of the upper biozones, A to C, is relatively constant across the Mukhaizna field, and some consistency in log character is also apparent. However Biozone D varies greatly in thickness and is the most internally heterogeneous in terms of log character. This, and the marked discontinuity in the palynological succession at the Biozone C/D boundary, suggests a possible break in the depositional sequence at the top of Biozone D.
Siliciclastic sedimentation in the interlude between two Neoproterozoic glaciations, Mirbat area, southern Oman: A missing link in the Huqf Supergroup?
Authors: Rieu Ruben , Allen Philip A. 
Published: October 2021

ABSTRACT
The Huqf Supergroup in Oman contains an exceptionally well-preserved and complete sedimentary record of the Late Neoproterozoic era, including the oldest components in some of Oman’s hydrocarbon plays. Outcrops of the Huqf Supergroup in northern and central Oman are now well-documented. However, a key succession in the Mirbat area of southern Oman, the Mirbat Group, which includes a stratigraphic interval missing elsewhere in the Arabian Peninsula, remains poorly understood. The &lt;1.5 km-thick Cryogenian (850–635 Ma) Mirbat Group comprises an essentially continuous succession of little-deformed sedimentary rocks containing two glacial intervals separated by c. 1 km of non-glacial marine deposits. The lowermost glacial interval (Ayn Formation) occupies deep paleovalleys incised into crystalline basement. The overlying Arkahawl Formation records at its base a major post-glacial transgression over the previous basin margin and a 300 to 400 m-thick turbidite complex consisting of 1 to 5 km-wide, coarse-grained depositional lobes embedded vertically and laterally in fine-grained distal turbidite fan deposits. Ayn Formation paleovalleys continued to serve as sediment transport routes for the coarse-grained turbidite complexes of Arkahawl times. The turbidite complex deposits gradationally pass up into a c. 500 m-thick unit of distal-marine mudstone and siltstone. The overlying c. 100 m-thick Marsham Formation records highstand deposition and the pulsed progradation of shallow-marine and fluvial deposits over offshore mudstone and siltstone in the approach to a second glaciation, represented by the Shareef Formation. The sedimentary succession described in this paper is believed to largely fill the stratigraphic gap present between the Ghubrah and Fiq formations in the Al Jabal al-Akhdar in northern Oman represented by an unconformity.
Dolomitization and porosity evaluation of the Cretaceous Upper Qamchuqa (Mauddud) Formation, Khabbaz oil field, Kirkuk area, northern Iraq
Authors: Al-Qayim Basim , Qadir Fuad M. , Albeyati Fawzi 
Published: October 2021

ABSTRACT
The Khabbaz Field in northern Iraq produces oil and gas from the Albian Upper Qamchuqa Formation, which corresponds to the Mauddud Formation of southern and central Iraq and the Arabian Gulf. The Formation is layered into Units A, B and C, of which Unit A is the main reservoir zone characterized by correlatable flow units and barriers/baffles. Units B and C generally have lower overall reservoir quality compared to Unit A. A detailed examination of cuttings, cores, and wireline logs from ten wells in the field revealed an important link between sedimentary facies, dolomitization, and heterogeneity of reservoir characteristics. The wide range of dolomite fabrics include microcrystalline, planar-e, planar-s, planar-p, non-planar as well as saddle and cement types. These fabrics imply successive phases of dolomitization, which profoundly influence the enhancement of reservoir character. Intercrystalline, micromoldic, and microvuggy porosity are the most influential byproducts of this dolomitization. Fracturing and stylolitization, in addition to the uniform network of intercrystalline pore systems, especially of the fine- to medium-crystalline dolomite, effectively contributed to the collective porosity and permeability of the reservoir.
Sedimentary facies and trilobite and conodont faunas of the Ordovician Rann Formation, Ras Al Khaimah, United Arab Emirates
Authors: Fortey Richard A. , Heward Alan P. , Miller C. Giles 
Published: October 2021

ABSTRACTThe Rann Formation occurs as unique ‘exotic’ rafts in front of the Semail Ophiolite in the northern Oman Mountains. Its Ordovician age has been poorly constrained and it is often associated with the Ayim rock unit, which has been considered Devonian, Carboniferous or Ordovician by different workers. Here we present new trilobite and conodont evidence for the Ordovician ages of the three members of the Rann Formation, which includes the Ayim. The members are readily distinguishable on sedimentological and faunal grounds.The Lower Member comprises shales, quartzitic sandstones and thin fossiliferous shell beds. Large Cruziana are common, as is lingulacean debris and, at several horizons, possible hyolithids. Assemblages of graptolites, acritarchs, trilobites (Neseuretus cf. arenosus and Taihungshania cf. miqueli) and conodonts (Baltoniodus sp., Drepanodus arcuatus, Drepanoistodus sp. and Protopanderodus sp., Scolopodus sp.) are considered to range in age from Floian to early Dapingian, late Early Ordovician. The Ayim Member (previously formation) consists of fossiliferous shales and griotte-like nodular bioclastic limestones. The member is distinguished by its red colour and by numerous orthoconic nautiloids. Conodont faunas (Complexodus cf. originalis, Eoplacognathus protoramosus, Dapsilodus sp., Cornuodus sp. and Panderodus sp.) imply a late Darriwilian, Middle Ordovician age. The Upper Member consists of siltstones and sandstones generally lacking bioturbation and with rare shell beds and faunas. Trilobites (Deanaspis goldfussii seftenbergi, Vietnamia teichmulleri and Dreyfussina taouzensis) and chitinozoans are interpreted to indicate an early-middle Katian, Late Ordovician age.The three members represent shallow-marine deposits on a continental shelf subject to changing sand supply, storm-wave activity and sea-bottom oxygenation. The three periods of deposition, Floian – early Dapingian, late Darriwilian and early – middle Katian, correspond to highstands of Paleo-Tethys that also flooded interior Oman and Arabia. The limited burial and lack of metamorphism of the Rann is remarkable given its proximity to the Semail Ophiolite and to subduction related metamorphic rocks occurring nearby.
The Upper Jurassic–Cretaceous petroleum system of southern Iraq: A 3-D basin modelling study
Authors: Abeed Qusay , Littke Ralf , Strozyk Frank , Uffmann Anna K. 
Published: October 2021

ABSTRACT
A 3-D basin model of the southern Mesopotamian Basin, southern Iraq, was built in order to quantify key aspects of the petroleum system. The model is based on detailed seismic interpretation and organic geochemical data, both for source rocks and oils. Bulk kinetic analysis for three source rock samples was used to quantify petroleum generation characteristics and to estimate the temperature and timing of petroleum generation. These analyses indicate that petroleum generation from the Yamama source rock (one of the main source rocks in the study area) starts at relatively low temperatures of 70–80°C, which is typical for Type II-S kerogen at low to moderate heating rates typical of sedimentary basins. Petroleum system analysis was achieved using the results from 1-D, 2-D, and 3-D basin modelling, the latter being the major focus of this study. The 1-D model reveals that the Upper Jurassic–Lower Cretaceous sediments are now within the oil window, whereas the formations that overlie the Yamama Formation are still immature in the entire study area. Present-day temperature reflects the maximum temperature of the sedimentary sequence, which indicates that no strong regional uplift affected the sedimentary rocks in the past. The 3-D model results indicate that oil generation in the Yamama source rock already commenced in the Cretaceous. At some locations of the basin this source rock reaches a present-day maximum temperature of 140–150°C. The most common migration pathways are in the vertical direction, i.e. direct migration upward from the source rock to the reservoir. This is partly related to the fact that the Lower Cretaceous reservoir horizons in southern Iraq directly overlay the source rock.
Five buried crater structures imaged on reflection seismic data in Saudi Arabia
Authors: Neville Allen S. , Cook Douglas J. , Afifi Abdulkader M. , Stewart Simon A. 
Published: October 2021

ABSTRACT
Reflection seismic data acquired for hydrocarbon exploration in Saudi Arabia have revealed five buried crater structures ranging in diameter from 5 km to 34 km. These structures have little or no present-day surface expression and span a range of ages from Ordovician to Cenozoic. The Saqqar structure (29°35′N, 38°42″E) is 34 km in diameter and is formed in Devonian siliciclastics. The structure is partially eroded and is unconformably overlain by Upper Cretaceous and Paleogene strata up to 400 m thick. The Jalamid structure (31°27′N, 39°35″E) is 19 km in diameter at Lower Ordovician level and is infilled by Middle Ordovician sediments, at a present-day depth of 4,500 m. The Banat Baqar structure (29°07′N, 37°36″E) is 12 km in diameter at Middle Ordovician level and infilled by Upper Ordovician sediments, at a depth of 2,000 m. The Hamidan structure (20°36′N, 54°44″E) is 16 km in diameter at Paleogene level and is overlain by a thin veneer of Recent sediment. The Zaynan structure (20°23′N, 50°08″E) is 5 km in diameter and affects Triassic sediments at depth of 3,800 m, and is infilled by Jurassic strata. In addition to reflection seismic imaging, various amounts of gravity and magnetic data and drilled wells are available in or near these structures. Various models including impact cratering are discussed here for each structure. One structure (Saqqar) has yielded quartz grains with possible shock metamorphic features that, contingent on future work, may support a meteorite impact crater interpretation.