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Seventh Arabian Plate Geology Workshop: Pre-Cambrian to Paleozoic Petroleum Systems in the Arabian Plate
- Conference date: December 9-13, 2018
- Location: Muscat, Oman
- Published: 09 December 2018
1 - 20 of 25 results
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Early Tectonic Evolution Of Oman Revisited: Implications for the evolution of North Eastern Gondwana and for the oldest hydrocarbon systems in Arabia
Authors Irene Gomez-Perez and Andy MortonSummaryThe Precambrian tectonic setting is important to understand the oldest petroleum systems of Oman, including the distribution of our main source rocks in the Huqf Supergroup, the reservoirs of the Nafun, Ara, Nimr and Haima plays, the basin subsidence history and diagenesis, and the early deformation history and trap creation.
Recent multidisciplinary studies, including sedimentology, heavy minerals and detrital zircon geochronology, support that Oman formed at the western margin of the Indian Shield (Eastern Gondwana) during the Neoproterozoic (Tonian), and that it only collided with the Arabian-Nubian Shield (Western Gondwana) in the Early Cambrian (~525 Ma ago). This resulted in the formation of the Western Deformation Front, which marks the final suture between East and West Gondwana. Oman stayed as part of Arabia after Permian-Jurassic Gondwana break-up. These tectonic changes are tracked by depositional evolution, tectonic/magmatic events as seen by detrital zircon geochronology, and sediment distribution patterns.
Our results entail a significant update to our present tectonic evolution and plate reconstruction models of eastern Arabia, and to our understanding of the early petroleum systems of Oman.
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The Precambrian succession of Oman from Platform to Basin: Predicting reservoir and source rock distribution
Authors Irene Gomez-Perez, Suleiman Farqani, Sven Scholten, Alban Rovira and Badar BaloushiSummaryBased on recent multidisciplinary studies of the Precambrian succession of Oman, both in PDO cores and in outcrops, a new correlation from type sections in outcrops to the subsurface is proposed. The results have implications for source and reservoir rock distribution, stratigraphy, and Precambrian tectonic setting and evolution of Oman.
The type Precambrian Nafun Group sections are found in the Huqf outcrops of central Oman, and represent a proximal, continental to shallow marine sequence up to ~2000 m thick. The succession studied in the subsurface is ~800 m thick and dominated by deeper water, basinal deposits with numerous source rock intervals and poor potential as conventional reservoirs, more alike the Precambrian succession exposed in north Oman.
Reservoir rocks are proven in shallow water carbonate deposits of the Khufai and Buah Formations, and are possible in clastic deposits of the Masirah Bay Formation. The best source rocks are found in basinal deposits of the Masirah Bay, Khufai and Buah Formations, and were deposited during transgressive system tracks.
Paleofacies maps and regional distribution support Ediacaran deposition controlled by regional thermal subsidence along a passive margin on the eastern side of the Mozambique Ocean.
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Pre-Khuff subsurface stratigraphy in Kuwait
Authors Saifullah K Tanoli, Riyasat Husain, Abrar Al-Bloushi, Andy Horbury and Patrick ClewsAbstractOnly a few wells were drilled through the Pre-Khuff section in Kuwait and therefore limited data is available. A composite pre-Khuff stratigraphic section is attempted from this data by utilizing age dating data, the distinctive heavy mineral assemblages and by correlating with regional analogues.
In north Kuwait, the oldest sediments encountered are evaporites overlain by carbonates likely belonging to the Hormuz Group of Infra-Cambrian to Early Cambrian age. The Permo-Carboniferous Unayzah Formation unconformably overlies these carbonates. In south Kuwait these strata are missing and the Upper Permian Khuff Formation directly overlies on the older sediments.
The oldest sediments in south Kuwait consist of deformed, varve like deposits of finely laminated siltstone and mudstone probably belonging to the Murdama Group of Lower Ediacaran age. The overlying Rubtayn / Mataar Formation of possible latest Precambrian (Ediacaran) to earliest Cambrian age is made up of polymictic conglomerate, red sandstone and mudstone. The Badayi Formation overlies this sequence and consists of volcanics and volcaniclastic tuffs. These are overlain by red sandstone, siltstone and mudstones that could be laterally coeval to the Hormuz Formation.
Heavy minerals in the Ediacaran to earliest Cambrian strata are typified by apatite while zircon is dominant in the Unayzah Formation.
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Insights into the Unayzah Formation and the Basal Khuff Clastics in North Kuwait
Authors Saifullah K Tanoli and Abrar Al-BloushiAbstractA continuous core of about 280 feet covering Basal Khuff Clastics, and the upper Unayzah Formation was cut in a North Kuwait well. The Unayzah Formation in the cored interval consists of four main lithologies. These include; 1) stacked normally graded braided fluvial coarse pebbly sandstones, 2) high angle cross bedded sandstone likely involves eolian reworking, 3) flood plain / distal alluvial fan red colour mudstones, and 4) dark colour mudstones and siltstones which were deposited in backswamp and marsh type settings. This latter facies locally contain impoverished palynofloral assemblages and the associated beds have indications of tidal influence.
The Basal Khuff Clastics consist of 1) amalgamated sandstone, 2) bioturbated sandstone and siltstone, 3) heterolithic black carbonaceous shale with sandstone interbeds, and 4) interbedded sandstone, siltstone and dolomite facies. These sediments were deposited in coastal plain environments representing tide influenced channels, crevasse splay, interfluve, and coastal marsh / lagoon environments, prelude to the onset of a major transgression.
With the exception of ?eolian sandstone, due to authigenic illitic clay development, compaction, and the quartz cementation the reservoir potential in these sediments is reduced.
Based on the limited palynofloral information, age of these strata is most likely Kazanian to Tatarian.
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A new insight into understanding the middle Cambrian Miqrat reservoir in the North of the Sultanate of Oman: Implication for exploration and development strategies
Authors Nadeem Al Balushi, Othman Al Harrasi and Timothy LeeAbstractIn the past decade, Petroleum Development Oman (PDO) has been actively drilling deep tight gas wells targeting structural four way dip closures in the Miqrat Formation (middle Cambrian). The Miqrat Formation was widely deposited in an arid to semi-arid continental setting in alluvial and playa/sabkha environments.
The wide distribution of the Miqrat formation and the lack of high resolution seismic together with unavailability of dense well information imposed various challenges in developing accurate subsurface depositional models. The play depositional model was constructed as simplistic as possible assuming a wide-spread playa which tends to be sandy in the south and muddier toward the north. In addition, the previous models were forcing the correlations to fit the entire reservoir subdivisions (Upper, Middle & Lower) to be present within the play domain. This served the regional understanding for prospect identification. However, when zooming into field-scale areas it becomes obvious that the depositional model needs further refining to understand the well data and the flow behaviors in various domains.
Recently, with the arrival of high resolution wide azimuth seismic data and the availability of denser well penetrations, a relook was applied to the previous depositional model by integrating various multidisciplinary inputs including: well log evaluations, seismic inversion for reservoir characterization, well test results and pressure measurements. The data integration revealed that the Miqart reservoir properties and thickness are highly influenced by the paleo structural elevation variations and the accommodation space post the Angudan unconformity (poor properties close to the highs). These variations resulted in lateral change to thinner/poorer units or onlaps on dominant highs, and the existence of capillary trapping ( Figure 1 ). As a result, the tighter and thinner facies retained significant amount of water which did not succeed to get flushed by late gas charge due to capillary barriers. Therefore, wells which are drilled in good reservoir properties in a structurally down dip position show better gas saturation with high gas and low water production rates in comparison to the wells which are drilled up dip in poor properties within the same traps ( Figure 2 ).
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Reservoir Characteristics of the Late Ordovician in The Rub' al-Khali Basin, Kingdom of Saudi Arabia
Authors Z. Andegeorgs, Kok G. Mah, J. Ismail and M. HusniAbstractIn the Rub' al-Khali Basin, the Late Ordovician glacial sediments were deposited in a vast water body where laterally shifting depositional environments resulted in lateral facies changes, from well-sorted glacio-fluvial reservoir sandstone to diamictite deposits. The predominantly fluvial channel deposits, consisting of medium to very fine grained sheet sands and interfluve muddy siltstones, were widely distributed, the thicknesses of which ranged from tens to several hundreds of feet. In core, glacial outwash channels, braided plain sands, and lacustrine shale layers with drop-stones from melting ice were observed.
The net sand-to-gross ratio is generally high due to the sedimentation dynamics, whereby moving icepressured meltwater jets became sorting agents in the process of glacial sedimentation. In the central Rub' al-Khali, core studies from drilled wells and associated log responses show variable reservoir quality. The overall reservoir quality is controlled by a number of primary and secondary factors. Primary controls are related to sedimentation and the depositional environment, which are manifested in these type of facies, grain size and sorting. Well-sorted, coarse sandstone is associated with high energy currents, and is mainly present in the fluvial system. Non-reservoir facies such as lacustrine shale and diamictite deposits are associated with low energy lacustrine or deep water deposits. The characteristic high net-to-gross ratio observed in the Rub' al-Khali Basin is primarily due to grain sorting. Thin sections from core indicate that mechanical compaction and silica cementation had, in areas, effected reservoir quality.
Post-deposition diagenesis, particularly clay coatings, preserved intergranular porosity by preventing continued silica growth on sand grains. Mineral dissolution is not prevalent, and likely did not have significant effect on porosity. Evidence of pressure solution, such as micro-stylolites and sutured contacts between grains are present, indicating sandstone grains were subjected to significant mechanical compaction. Compaction is related to the depth of burial, and its impact on reservoir quality varies throughout the Rub' al-Khali Basin. Silica cementation appears to be sourced from stress inducing stylolites, where the silica cement is formed around the grains.
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