More than 60 core and oil samples from different wells and different oil and gas fields were selected to<br>determine the thermal history, hydrocarbon generation and migration in four important formations<br>from the Upper Jurassic- Lower Cretaceous period of the Mesopotamian Basin (Zubair subzone),<br>southern Iraq. The study area is situated in the southern part of the basin and covered many important<br>oil and gas fields in the Basrah province. Only few detailed geochemical studies on this important<br>petroleum systems have been published so far (Alsaadoni and Aqrawi, 2000). The aim of this study is<br>to get a more thorough understanding of source and reservoir rock characteristics of the Sulaiy,<br>Yamama, Ratawi and Zubair formations. Sediment and oil samples from important producing oil and<br>gas fields like Rumaila, Nahr Umar, Subba, Zubair, Ratawi, West Qurnah and Toba oil fields were<br>analysed by geochemical and organic petrological methods.<br>TOC-analyses, Rock-Eval pyrolysis as well as GC-FID and GC-MS measurements on solvent extracted<br>and fractionated samples were performed. To further estimate the thermal maturity of sedimentary<br>rocks vitrinite reflectance values were measured.<br>Results of this analytical work show that the studied formations are mature and have reached the oil<br>window. Most of the samples in the studied formations can be classified as type II/III or type III<br>kerogen. This coincides with a suboxic-anoxic depositional environment of Sulaiy and Yamama<br>formations while the Zubair formation is suggested to derive from a distal suboxic shelf deltaic<br>environment and the Ratawi formation from an inner shelf neritic environment. Due to the high TOC,<br>S2 and HI values, the Sulaiy, Ratawi, Yamama formations and the shales within Zubair formation are<br>considered as good petroleum source rocks.<br>Detailed molecular geochemical studies revealed a variabiliy in pristane/phytane ratios, CPI values and<br>biomarker ratios, both for source rocks and oils. These parameters were further used to establish oil<br>families and to correlate oils with their respective source rocks.<br>References<br>-Alsaadoni, Fadhil N. and Aqrawi, Adnan A.M., 2000, Cretaceous sequences stratigraphy and petroleum<br>potential of the Mesopotamian basin, Iraq: SEPM (Society for Sedimentary Geology), special<br>publication No.69, ISBN 1-56576-075-1, p.315-334.


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