Mishrif Formation Oil Biomarkers Used to Assess Hydrocarbon Generation, Migration Path and Accumulation Sites in the Ratawi, Zubair, Rumaila North and South Oil Fields, Southern Iraq
Thamer K. Al-Ameri1* and Amer J. Al Khafaji2
1Baghdad University, Iraq
2Babylon University, Iraq
*[email protected]
The reservoir rocks of the Mishrif Formation in Iraq have a porosity of between 25% and 28%. Oil analysis indicated that the source rocks have the following properties: (1) carbon-ate rocks inter-bedded with shale deposited in reduced marine environment with low salin-ity and type II kerogen. This is based on biomarkers of Carbon Preference Index (CPI), Phytane, Pristane, n-alkanes of steranes and hopanes, as well as Early Cretaceous in age based on the sterane ratio of C28/C29 and C26/C29 (C=Carbone), the presence of the dinoflagellate cyst species Pseodoceratium pelliferum, and the ratio CPI, TS/(Ts+Tm), Pr/nC17 and Ph/nC18 biomarkers, and the brown colour of the dinoflagellate cysts and Tasmanites under light microscope. This oil analysis indicated that most of the oil accumu-lated in the Mishrif Formation might have been sourced from the Upper Jurassic Najmah and Sargelu and the Lower Cretaceous Sulaiy formations. Palynological analysis was con-ducted on samples taken from cores. Based on the abundance of amorphogen palynofacies, increasing foraminiferal test linings, and the thermally mature high total organic carbon (up to 8%) it appears that the main oil expulsion was mainly from the Sulaiy Formation. This formation was deposited in a distal suboxic-anoxic basin. Moreover, pyrolysis analysis of these core rocks indicated oil and gas generation from the Sulaiy Formation. This conclu-sion was based on their position in the diagram of Van Krevlen, scattered remains of hydro-carbon with TOC, and the hydrogen index with Tmax. The oil was generated and expelled during the Miocene from a depth of 5,000-5,357 m and charged the Mishrif reservoir in the traps formed earlier during the Late Cretaceous Period.
AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain