Dolomitization and porosity evaluation of the Cretaceous Upper Qamchuqa (Mauddud) Formation, Khabbaz oil field, Kirkuk area, northern Iraq

The Khabbaz Field in northern Iraq produces oil and gas from the Albian Upper Qamchuqa Formation, which corresponds to the Mauddud Formation of southern and central Iraq and the Arabian Gulf. The Formation is layered into Units A, B and C, of which Unit A is the main reservoir zone characterized by correlatable flow units and barriers/baffles. Units B and C generally have lower overall reservoir quality compared to Unit A. A detailed examination of cuttings, cores, and wireline logs from ten wells in the field revealed an important link between sedimentary facies, dolomitization, and heterogeneity of reservoir characteristics. The wide range of dolomite fabrics include microcrystalline, planar-e, planar-s, planar-p, non-planar as well as saddle and cement types. These fabrics imply successive phases of dolomitization, which profoundly influence the enhancement of reservoir character. Intercrystalline, micromoldic, and microvuggy porosity are the most influential byproducts of this dolomitization. Fracturing and stylolitization, in addition to the uniform network of intercrystalline pore systems, especially of the fine- to medium-crystalline dolomite, effectively contributed to the collective porosity and permeability of the reservoir.