A Dual Petroleum System in the Eastern Onshore Abu Dhabi

Abstract

This study focuses on new exploration opportunities in the northeastern onshore area of the Emirate of Abu Dhabi where few commercial hydrocarbon discoveries are reported until recently. An exploration well newly drilled within the studied area has confirmed a total of five formations with oil and gas accumulations. A comprehensive geochemical analysis was conducted to identify potential source rocks and to correlate hydrocarbon with source rock. Furthermore, the effective kitchen and hydrocarbon migration/charging process were investigated by a simple 1D basin modeling approach. The key findings are:Rock-Eval pyrolysis suggests that at least three potential source rock formations are present in the (Cretaceous) Aptian, Cenomanian and Campanian. Any source rocks in and below the Jurassic are not fully understood in the studied area.Biomarker fingerprints indicate a possibility that oil in the Upper Cretaceous reservoirs and oil in the Lower Cretaceous reservoirs have been delivered from a different source rock and migration process.Oil in the Upper Cretaceous tends to exhibit a lower API gravity with no or trace associated H2S, suggesting an earlier-generated oil.Oil in Lower Cretaceous has a light to very light API gravity with minor to fair H2S content. This implies a mixed sourcing from a matured / gas source rock and post matured deep kitchen. The findings tell that two independent petroleum systems are simultaneously effective in the area. An Upper and Mid System is shallower, providing an early oil matured system that creates mostly oil accumulations in Upper Cretaceous. The system is situated in a foreland basin associated with obduction tectonism in the Late Cretaceous to Tertiary. The older system is a deeper late/gas matured system that creates both oil and gas accumulations in the Lower Cretaceous. The system is associated with the thermal subsidence of a thick passive margin basin which ranges from the Permian to Middle Cretaceous. The multiple petroleum systems in the eastern onshore Abu Dhabi region have been implied by a lot of evidence but have been less explicitly discussed. This study organizes the outline of these systems and delineates the potentialities for exploration and appraisal for the study area.