Asmaa Mousa, Salah A. Hussain
One of the most important reservoirs in the southern part of Iraq is the Mauddud Formation. The microfacies, diagenesis, and depositional environment of the Mauddud Formation were identified in four wells in the Ratawi Field (RT-2, RT-4, RT-17, and RT-19). Petrographic analysis of 114 thin sections revealed four main microfacies and five sub-microfacies within the formation. Skeletal grains are more abundant than non-skeletal grains, providing strong evidence that the formation was deposited in a shallow marine environment, including four depositional settings: platform interior open marine, platform interior restricted, platform-margin sand shoal, and reef environment. Diagenetic processes were also classified, revealing that the formation was affected by several alterations. Some processes enhanced porosity, such as dissolution, which produced various porosity types, including intraparticle, interparticle, vuggy, channel, cavern, moldic, and fracture porosity. Other processes negatively affected the porosity and reservoir quality, particularly cementation, with three identified cement types: blocky, granular, and drusy. Dolomitization locally enhanced reservoir quality by creating intercrystalline porosity and improving permeability. In contrast, the chemical compaction, as represented by stylolite formation, had a negative effect, reducing the porosity through pressure solution and acting as a barrier to fluid flow.