• Mesopotamian Basin;
  • Iraq;
  • Rumaila oilfield;
  • Zubair oilfield;
  • Sulaiy Formation;
  • source rocks;
  • organic geochemistry

This paper reports on the hydrocarbon potential of subsurface samples from the Upper Jurassic Lower Cretaceous succession at the Rumaila (North and South), Zubair, Subba and West Qurna oilfields in southern Iraq. A total of 37 fine-grained core samples of the Sulaiy, Yamama, Ratawi and Zubair Formations from ten wells were analyzed. Contents of organic carbon and sulphur were measured; other analyses included Rock-Eval pyrolysis, optical microscopy in incident light, solvent extraction and gas chromatography of non-aromatic hydrocarbons. The results indicated that the samples from the Cretaceous succession (Yamama, Zubair and Ratawi Formations) are at moderate levels of thermal maturity, whereas samples from the Upper Jurassic – Lower Cretaceous Sulaiy Formation are at a stage of thermal maturity beyond peak oil generation. According to the results of this study, the Sulaiy Formation is an excellent highly-mature source rock and it is probably responsible for the generation of large quantities of oil in the study area. The samples differ with respect to their organic fades and biomarker distribution, indicating that palaeo depositional conditions varied significantly.