Dolomitization and Reservoir Characterization of the Creataceous Upper Qamchuqa Formation, Khabaz Oil Field, Kirkuk Embayment, Northern Iraq

Basim J. Al-Qayim¹, Fuad Qadir¹, and Fawzi Al-Biaty^2
1Department of Geology, Sulaimani University, Sulaimaniah, Iraq
²Survey Department, Kirkuk Technical College, Kirkuk, Iraq

The Platform carbonate sequence of the Upper Qamchuqa Formation (Albian) of Kirkuk embayment , northern Iraq, is extensively affected by pervasive dolomitization. These dolomite rocks become the most productive Cretaceous reservoirs of several oil fields in the area. Core and log data analysis of ten wells from Khabaz oil field in the area shows that understanding the dolomitization impact would greatly enhance reservoir quality prediction model. These carbonates are about 120 thick and consist of three basic lithologic units from top: Unit (A) alternation of of sucrosic dolomite and dolomitized limestone, (B) Massive coarse crystalline dolomite with intercalations of dolomitic marl, (C) Alternating shale , marly limestone and fine crystalline dolomite. The upper unit include six good quality reservoir units of variable thickness but closely similar petrophysical properties. Thickness of these units is ranging between 3-10 meters, and consists often of saturated fairly homogenous dolostone of fine to medium crystalline planar-s to Planar-e dolomite mosaic with excellent intercrystalline pore network. Porosity ranges between 10-25% and permeability exceed in some case 50 md. Successive burial diagenesis lead to enhance their petrophysical properties by dissolving resistant undolomitized bioclasts which support the additional moldic and vug porosity. Overall fracturing of the reservoir enhance reservoir potentiality. The origin and paragensis of these dolomite is discussed in term of fluctuation of sea level and burial history.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas