Source Characteristics and Lateral Migration of Middle CretaceousPetroleum System in Western Abu Dhabi,Insight from Biomarker andReservoir Investigation

摘要

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 orpackstone around platform margin setting.Regional understanding believes that the in-situ Shilaif mudstoneis not mature enough to source the overlain Mishrif.So,it is inferred that the Mishrif reserves werecharged from Shilaif kitchen of regional syncline through over 100km lateral migration from south tonorth.However,this accumulation pattern seems presumptive as little solid evidence was reported and littlegeochemistry measurement have been done previously.To enhance understanding of the Shilaif source characteristics and figure out Shilaif-Mishrifaccumulation 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 resultsshows the in-situ Shilaif has abundant organic content with high TOC,HI and bitumen"A"with lowmaturity.Tmax of Shilaif mudstone yields an average value of 430°C and calculated vitrinite reflectanceabout 0.6,which means an early oil generation for in-situ Shilaif source.Oil-source correlation indicatesa higher maturity of crude oil in the Mishrif & Tuwayil than the in-situ Shilaif.Furthermore,similaritiesof biomarkers between Mishrif oil and the Ghurab syncline Shilaif source are proved.All these evidencesreveal the lateral hydrocarbon migration and accumulation northwards.For the migration pathway,it is inferred the regional unconformity of TopMishrif plays an important roleto transfer the hydrocarbon.In Western Abu Dhabi,truncation or depositional hiatus around TopMishrif arenot 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 showsin 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 insightinto accumulation rules of Cretaceous Petroleum system in Western Abu Dhabi and would guide the furtherexploration activity.