Hydrocarbon Habitats in the Mesopotamian Basin and Zagros Fold Belt of Iraq

A.S. Alsharhan
Middle East Geological Establishment, Al-Ain, United Arab Emirates

Commercial oil was discovered in 1927 in the Kirkuk structure, since then many oil and gas fields discovered ranked Iraq one of the top leading producing countries in the world. With its proved reserves of 113 BB of oil and 110 TCF of gas from 84 fields.
The main reservoirs are the Cretaceous carbonates and sandstones in the Mesopotamian Basin, and Tertiary Carbonates in the Zagros Basin. These are sealed either by shales or evaporites. These two basins are dominantly oil-prone, while free gas in countered locally in the Tertiary reservoirs along the eastern margin of the fold belt and in Lowe Paleozoic reservoirs of Western Desert.
The Jurassic Sargelu and Naokelekan Formations are the main source rock potential in the Mesopotamian Basin and Zagros fold belt. The shales in the Sargelu has TOC ranges from 2% to 6% with higher values of up to 20%; while in the Naokelekan from 3-9% and locally reaches 15%. The present HI values ranges from less than 100 to more than 600 mg HC/g TOC. In the Mesopotamian Maturities ranges from 1.2-1.5% Ro, while in the fold belt it ranges from 0.5-1.9 Ro. The oil generation connected in the late Cretaceous and reached completion in the late Paleogene.
Structural traps in Mesopotamian Basin are large, broad N-S striking basement-cored anticlines, while in the fold belt are dominated by NW-trending compressional folds that formed by inversion over extensional faults. Trap-forming mechanisms are due to reactivation of deep-seated faults and diapiric growth, synorogenic faulting and restricted movements. While in the fold belt traps development involved multiple phases of folding occurred in the late Cretaceous and was subsequently overprinted by late Cenozoic folding and faulting.

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