Microfacies and Depositional Analysis of Mauddud Formation in Selected Wells at Three Oilfields—Southern Iraq

Mauddud Formation (Late Albian–Early Cenomanian) is one of Iraq’s most important carbonate hydrocarbon reservoirs. Fifty-four core samples and one hundred fifty thin sections were made from several wells of Mauddud Formation in Ratawi, south Rumaila, and west Qurna oilfields, southern Iraq. The mineralogy of this formation is limestone and dolomite. The microfacies analysis results in five main microfacies associated with Mauddud Formation, including mudstone, wackestone, packstone, grainstone, and dolostone. In addition to ten submicrofacies including planktonic mudstone, benthic wackestone, bioclastic wackestone, algal wackestone, peloidal wackestone, bioclastic packstone, benthic packstone, benthic grainstone, bioclastic grainstone, and peloidal grainstone. These facies are indicated to be shallow restricted, lagoon, shoal, open marine, and mid-ramp environments. It was deposited on a shallow carbonate platform with a ramp setting. Several digenetic processes are affected in this formation: micritization, neomorphism, dissolution, cementation, dolomitization, and compaction are the main diagenetic processes. Dolomitization and dissolution processes improved the porosity and permeability with higher reservoir quality while cementation reduced the reservoir quality.