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Hydrocarbon Generation Potential and Source Rocks Characteristics of Upper Jurassic - Lower Cretaceous Formations in the Southern Part of the Mesopotamian Basin (Zubair Subzone), Southern IraqGold Open Access

Authors: Qusay H. Abeed, Sabine Heim, Amer Alkhafaji and Ralf Littke
Event name: GEO 2010
Session: Petroleum System Analysis III
Publication date: 07 March 2010
Organisations: EAGE
Language: English
Info: Abstract, PDF ( 33.32Kb )

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

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