Abstract

In the western Abu Dhabi, oil fields have been discovered from the Mishrif reservoir (Cenomanian/Turonian). These fields are found in shoal/reef related stratigraphic prospects and composed of grainstone or packstone around platform margin setting. Regional understanding believes that the in-situ Shilaif mudstone is not mature enough to source the overlain Mishrif. So, it is inferred that the Mishrif reserves were charged from Shilaif kitchen of regional syncline through over 100km lateral migration from south to north. However, this accumulation pattern seems presumptive as little solid evidence was reported and little geochemistry measurement have been done previously.

To enhance understanding of the Shilaif source characteristics and figure out Shilaif-Mishrif accumulation rules, cuttings, cores from Shilaif and oil samples from Mishrif & Tuwayil were taken. Subsequently, geochemistry assay, oil-source correlation and related research were carried out. The results shows the in-situ Shilaif has abundant organic content with high TOC, HI and bitumen "A" with low maturity. Tmax of Shilaif mudstone yields an average value of 430°C and calculated vitrinite reflectance about 0.6, which means an early oil generation for in-situ Shilaif source. Oil-source correlation indicates a higher maturity of crude oil in the Mishrif & Tuwayil than the in-situ Shilaif. Furthermore, similarities of biomarkers between Mishrif oil and the Ghurab syncline Shilaif source are proved. All these evidences reveal the lateral hydrocarbon migration and accumulation northwards.

For the migration pathway, it is inferred the regional unconformity of TopMishrif plays an important role to transfer the hydrocarbon. In Western Abu Dhabi, truncation or depositional hiatus around TopMishrif are not as pronounced as Eastern Mishrif platform, but obvious exposure as well as leaching evidence could be observed from uppermost Mishrif and Tuwayil through core investigation. Besides, almost all the oil shows in Mishrif concentrate around the interface, which further proves the role of the unconformity.

The study on Shilaif source characteristics and hydrocarbon migration mechanism enhances the insight into accumulation rules of Cretaceous Petroleum system in Western Abu Dhabi and would guide the further exploration activity.

You can access this article if you purchase or spend a download.