Geochemical Evaluation, Thermal Maturation and Petroleum Potential of the Upper Jurassic-Lower Cretaceous Formations in the Southern Iraq Basin

R. Paul Philip¹ and Abdullah Ali^2
1University of Oklahoma, Norman, OK
²South Oil Company, Basra, Iraq

The Upper Jurassic (Qutnia and Suliay) and Lower Cretaceous (Yamama Ratawi, Zubair, Shuaiba, Nahr Amr and Mishrif) formations of southern Iraq were characterized using Rock Eval pyrolysis, gas chromatography, gas chromatography-mass spectrometry and isotopic analysis in order to evaluate their thermal maturation and hydrocarbon generation potential. All units contain predominantly marine organic matter (Type II and III), in sufficient quantities to be considered potential oil prone source rocks. The Rock-Eval geochemical data indicate that the distribution of %TOC in the study area varies from good to poor. Accumulation of organic matter occurred in low energy, marine environments changing from shallow to deep shelf and open shallow marine. The data indicate that the Upper Jurassic formations are thermally mature with moderate source potential. The Cretaceous formations have entered the oil window and have fair to good source potential. Lower Cretaceous formations in this study consist of shales and carbonates deposited under anoxic conditions. Biomarker distributions in the crude oils suggest that the majority of the oils are primarily derived from algal and bacteria organic matter present in the carbonate source rocks. The carbonate derived oils are probably sourced from the Turonian (Mishrif) and Aptian (Zubair). The one exception to this appeared to be the Albian Nahr Amr oil which is thought to have been sourced from a shale source rock, of unknown origin at this time, containing significant amounts of terrestrial organic matter.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece