Present and Potential Oil Systems in the Mesozoic Strata of the Mesopotamian Basin, Southern Iraq

By

Fadhil N. Sadooni¹

(1) United Arab Emirates University, Al-Ain, United Arab Emirates

 Mesozoic strata of the Mesopotamian Basin host more than 90% of Iraq’s recoverable oil reserve. There are six present oil systems; all of them are within the Cretaceous rocks, with several other potential systems mainly in the Cretaceous and Jurassic strata. The present petroleum systems are found within the Sulaiy and Yamama formations of the lower Berriasian-Valanginian cycle; the Ratawi and Zubair formations of the Valanginian-Barremian cycle, the Nahr Umr and Mauddud formations of the middle Aptian-Albian cycle, the Mishrif Formation of the Cenomanian-lower Turonian cycle, the Khasib and Tanuma formations of the Turonian-lower Campanian cycle and the Hartha Formation of the Campanian-Maastrichtian cycle.

These stacked reservoirs are bounded by local and regional seals and charged mainly by Lower Cretaceous and Upper Jurassic source rocks.

Potential oil systems include the Upper Jurassic sediments of the Najmah Formation, the extension of the Ratawi, Yamama and Mishrif reservoirs outside the present areas, the presence of oil in formations that are not considered as reservoirs yet such as the Tanuma and Sa’di and the limestone member of the Ahmadi Formation, the stratigraphic traps resulted from the basin-margin rudist buildups within the Shu’aiba and Mishrif formations, or the clastics of Zubair and Nahr Umr formations, and those requiring the use of modern technology such as the delineation of any possible dolomite reservoirs within the evaporites of the Gotnia formation.