Geochemical study of some Cretaceous rocks from Kuwait: comparison with oils from Cretaceous and Jurassic reservoirs

Geochemical study of some Cretaceous rocks from Kuwait: comparison with oils from Cretaceous and Jurassic reservoirs F.H. Abdullaha , J. Connan

Abstract

A set of 18 Cretaceous rock samples from wells drilled in the Raudhatain and Minagish Oil Fields and 10 oil samples from Cretaceous reservoirs (Raudhatain, Bahra, Burgan and Minagish Oil Fields) were characterized using geochemical methods including compound-specific carbon isotope analyses of n-alkanes and isoprenoids. In addition, one oil (Miqua) from the Jurassic (Marat Formation) of the Great Burgan Oil Field was included in the study. Despite having high organic carbon content in some samples, the Burgan and Zubair formations and the Ratawi Shale Member, of Albian to Valanginian age, are not source rocks for the oils for several reasons, but primarily due to lack of correlation of molecular and isotope chemistry as well as a humic organic matter type. These results are consistent with the corresponding depositional conditions for these rocks, which are deltaic/estuarine in the Burgan Formation and littoral/ deltaic in the Zubair Formation. The Minagish and Sulaiy Formations of Late Jurassic to Cretaceous age appear to be potential source rock candidates based on their molecular and bulk isotope geochemistry. Detailed isotopic analysis using individual normal and isoprenoid C15+ alkanes did not provide a good correlation between these possible source rocks and the oils. However, one sample from the Sulaiy Formation was found to be comparable to the oils. The oils belong to the same genetic family and were expelled from a source rock with a dominant carbonate lithology (e.g. the Sulaiy-Minagish Formations). These formations contain sulphur-rich, amorphous kerogen as observed in recent, shallow marine shelf deposits.