Geological Setting and Hydrocarbon Potential in the Mesopotamian Basin, Iraq

A. S. Alsharhan¹ and K. H. Habib^2
1 Middle East Geological Enterprises, Al Ain, United Arab Emirates
² Qatar Petroleum, Doha, Qatar

The Mesopotamian basin is about 200km wide, NW-SE trending sector of the unstable shelf that immediately border the Salman Zone of the stable shelf to its west. It is wedged between the Salman Zone and the Zagros folded zone to its east, narrowing until it disappears northwards toward NE Syria. The basin absence of surface manifestations of folds although long buried structures of NW-SE trends are common in its northern part, and N-S trends in its southern part, while its western part is relatively tectonically quite. The basin is underlain by numerous NW-SE trending folds and undergoing compressional folding.

The Jurassic Sargelu Formation is the main source rock potential. The shales in the Sargelu has TOC ranges from 2% to 6% with higher values of up to 20%. The present HI values ranges from less than 100 to more than 600 mg HC/g TOC. Maturities ranges from 1.2-1.9% Ro, and the oil generation commenced during the late Cretaceous and reached completion in the late Paleogene. The timing of oil generation and expulsion postdated the formation of major Plaeozoic and Mesozoic traps in the region. Trap-forming mechanisms are due to reactivation of deep-seated Precambrian faults and diapiric growth, synorogenic faulting in the Mesozoic and restricted movement in the Cenozoic.

The main reservoirs are Cretaceous and characterized by deltaic sandstones and carbonates in the Yamama, Zubair, Ratawi, Nahr Umr and Ahmadi. The carbonates contains an excellent petrophysical properties (porosity exceed 30% and permeability (D). The sandstone reservoirs has 1-30% porosity and 0.1 to 5D permeability. Shales represent an excellent and regional seals on these reservoirs.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005