Source Rocks of the Thamama Hydrocarbon in Abu Dhabi

Abstract

Abstract More than 80% of Abu Dhabi oil reserves are accumulated in the Thamama reservoirs. However, its source rock locations, thickness and richness distributions are not fully understood. Thamama hydrocarbons were generated and migrated from different source rocks including Diyab, Rayda, Thamama dense and Shuaiba basinal facies, in addition to a contribution from the deeper Paleozoic, Silurian Qusaiba and the Pre-Cambrian Huquf source rocks. The Oxfordian, Diyab high-energy Oolitic belts are prograding in westward direction, and have resulted in the development of Diyab intrashelf basin in west Abu Dhabi. At the end of the Kimmeridgian time, Abu Dhabi basin was tilted towards the east due to the opening of Arabian-Indian Suture. This tilting had completely shifted the high-energy Oolitic belts to prograde in eastward direction, which resulted in the development of Rayda source rock in east Abu Dhabi. The Thamama dense layers were deposited during the highstand system tract, which allowed some organic matter to be preserved; especially in intervals deposited below the wave base. The Shuaiba basinal facies were deposited in an intrashelf basin that was surrounded by the Shuaiba shelf facies. This resulted in restricted water circulation and anoxic conditions. Such depositional environment is reasonable for source rock preservation. The hydrocarbon generations from these different sources were mainly accumulated in a super-giant Paleo-structure that was located in the northeast onshore Abu Dhabi. This Paleo-structure was segmented by the Late Tertiary tilting, which resulted in remigrating its trapped hydrocarbon into the prominent Abu Dhabi fields. The development of Rayda source rock will increase the potentiality of finding additional unconventional hydrocarbon resources in east onshore Abu Dhabi. The high unconventional potential in this area can be attributed to the advanced level of source rock maturity and to the highly faulting and fracturing found in east onshore Abu Dhabi. The Rayda source rock maturity map confined the unconventional gas potential to the foreland basin while the unconventional oil potential is located to the south of this area (figure-10). Understanding the locations of Thamama source rock kitchens will facilitate the delineation of its migration pathways. This will reduce the exploration risk and help in detecting prospective areas for stratigraphic traps potential along the Thamama migration pathways over all Abu Dhabi.