Evidences for New Attractive Gas Exploration Targets in Abu Dhabi Upper Permian Section

Taher, Ahmed; Suwaidi, Ahmed S. Al; Al-Habshi, Ali Mohamed

doi:10.2118/118276-ms

All Days 2009

DOI: 10.2118/118276-ms

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Evidences for New Attractive Gas Exploration Targets in Abu Dhabi Upper Permian Section

Ahmed Taher

Ahmed S. Al Suwaidi²,

Ali Mohamed Al-Habshi³

Abstract: The great Paleozoic system of the Arabian Gulf forms one of the most prolific hydrocarbon producing systems in the world. The Primary elements of this system like source, reservoir, seal and traps are extended throughout the eastern Arabian Peninsula and have exceptional scale and quality. Modeling of the structural growth history, in conjunction with the hydrocarbon generation and migration in the area, has shown that early growth and charge were essential conditions for the formation of economic hydrocarbon … Show more

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Cited by 4 publications

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Tight Gas Exploration Potential of Middle Triassic to Early Jurassic Successions in Abu Dhabi

Taher

2012

All Days

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Middle Triassic to Early Jurassic formations were not previously considered as exploration objectives. Only a limited wells penetrate these formations and most of these wells were targeting the deeper Khuff and pre-Khuff reservoirs. Stratigraphically, the section is comprised of sequences of shallow marine mixed carbonates intercalating with shale, sandstone and anhydrite streaks. These formations, although they exhibit gradual thickening from the north towards the south direction, yet they show remarkable lateral consistency, both in lithology and log response. Primary and secondary porosity are generally poor in these formations, reflecting the deep burial depth and the intercalation of shale and anhydrite beds with the carbonate reservoirs. Structurally, the formations have been subjected to numerous phases of tectonic deformation that have affected the facies variations and reservoir development. Evidence indicates that the early phase of Qatar Arch development and the southeast Mender palaeohigh were tectonically active during the Triassic time. The Lower Jurassic and Upper Triassic formations have discontinuous and moderate source rock development. Sapropelic kerogen constitutes the dominant type of organic matter, however, also humic type is present but in minor quantities (Lutfi, 1987; Hassan, 1989). The top Triassic maturation modeling showed various degrees of thermal maturation ranging from mature to intensively mature stages. Interpretation of the maturation regime indicated that most of onshore Abu Dhabi is in the dry gas generation window. The southern offshore area is within the wet gas generation, while the northern offshore is still in the oil generation window. The relatively lean source rock intervals found within the Lower Jurassic and Triassic Formations suggest that there is a significant charge contribution from the deeper Silurian Hot Shale source rocks. Pronounced gas shows were experienced while drilling some of the offshore and onshore structures. The well data indicates that the Izhara, Hamlah, Minjur and Marrat Formations are developed in onshore Abu Dhabi. Sedimentary patterns, facies variations and log response of the Lower Izhara, Minjur and possibly Upper Gulailah Formations suggest the presence of shale gas developed in these formations.

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Tight Gas Exploration Potential of Middle Triassic to Early Jurassic Successions in Abu Dhabi

Taher

2012

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Hydrocarbon Habitat of the Early Permian Unayzah Formation in Abu Dhabi

et al. 2012

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The pre-Khuff principal hydrocarbon reservoir, Unayzah Formation, consists mainly of distal braid plain sandstones characterized by aeolian and sabkha facies with minor fluvial units. It extends between the pre-Khuff and the Hercynian unconformities. In Abu Dhabi, the Unayzah-A is further subdivided into three members, Members 1 and 2 are comprised of sandstone reservoirs and Member 3 consists of siltstone and shale sediments. Facies controls on reservoir quality are weak. The main controls on porosity reduction of the reservoir are mechanical compaction and silica cementation. Quartz cementation tends to be the most severe in the cleanest, coarsest sandstones and near certain fractures. The presence of clay mineral grain coatings, although reducing the permeability, but locally protects the rock from secondary quartz overgrowth and preserve the porosity to great depths of burial. Without the grain coating, porosity will decrease with depth until the reservoir rock is completely tight. Unayzah reservoir seals are provided by the Basal Khuff Clastics, tight Basal Khuff Carbonate and Middle Khuff Anhydrite. The Basal Khuff Carbonate seal does not appear to be regionally extensive but localized and potentially prospect specific. However, there are insufficient data to accurately define the seal for the Unayzah hydrocarbon accumulations. Due to lack of deep penetrations in Abu Dhabi, basin modeling for Silurian hot shale source rock is challenging. Therefore, much of the unknown source and tectonic information were derived from the surrounding countries. This comes from understanding the regional tectonics and depositional trends of the southeastern Arabian plate, which helped to extrapolate the source trends into the Abu Dhabi area. The basin model shows that oil from Silurian source rock was generated early in the basin history and was widespread by the Late Triassic (220 Ma). Significant gas generation occurred during Lower Cretaceous (140 Ma) and dominated the hydrocarbon system by Middle Cretaceous (110 Ma). During the Early Tertiary (50 Ma), the source rock was highly mature for gas generation and at present-day, the charge is still active in the north offshore of Abu Dhabi. The pre-Khuff charge history showed that the southern offshore and onshore structures are underfilled. The filling of these structures ranges between 50% and 80%, but in some onshore structures the filling is less than 50%. The middle and northern offshore structures are expected to be filled to spill point.

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Tight Hydrocarbon Exploration Potential in Central Onshore Abu Dhabi Giant Field

Taher

Aryani

Zaabi

2017

Day 4 Thu, March 09, 2017

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As the super-giant fields in the area continue to produce their hydrocarbon resources, there is a natural decline in production as the easy to access resources are going to be depleted in a few decades. Finding additional oil and gas resources to replace the produced hydrocarbon is representing major challenge. The hydrocarbon saturated tight layers, found in the super-giant onshore field, could represent an example for finding additional hydrocarbon volume that accumulated in a difficult trap style. The central onshore field tight layers were found in the successions extended from the Lower Cretaceous, Thamama Group down into the Upper Permian Khuff formation. The high hydrocarbon saturation found in the Thamama tight layers was previously interpreted as residual oil left behind during the vertical oil migration from the Upper Jurassic Hanifa source rock into the Thamama reservoirs. However, the current charge model assumes a lateral westward hydrocarbon migration from east onshore Abu Dhabi through the Thamama reservoirs and towards the major Abu Dhabi central onshore fields. The charge filling started from the top of the structure and down into the spill point and filled both, the porous and tight layers (figure 3). The differences are in the reservoir properties, which by using the technology improvement in the horizontal drilling and hydraulic fracturing, the tight zones hopefully will produce a significant volume of hydrocarbon. The Lower Jurassic and Triassic formations were not previously considered as exploration objectives. Only one well penetrated these formations and it was targeting the deeper Khuff reservoirs. Several attempts were made to test some of these formations, but they were found to be completely tight. The water recovered from such testings was most probably drilling fluids. The Khuff reservoirs high gas shows while drilling, the high hydrocarbon saturation of its interpreted logs do not match its negative testing results. The cause of failure is most probably related to the formation damage and the classical tools and methods used in the production test. In addition to that, the cement jobs were not quite successful, which will allow for the water leakage behind the casing.

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Evidences for New Attractive Gas Exploration Targets in Abu Dhabi Upper Permian Section

Cited by 4 publications

References 7 publications

Tight Gas Exploration Potential of Middle Triassic to Early Jurassic Successions in Abu Dhabi

Tight Gas Exploration Potential of Middle Triassic to Early Jurassic Successions in Abu Dhabi

Hydrocarbon Habitat of the Early Permian Unayzah Formation in Abu Dhabi

Tight Hydrocarbon Exploration Potential in Central Onshore Abu Dhabi Giant Field

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