Microfacies Analysis and Depositional Environment of the Fatha Formation for Two Oil Wells North of the Salahuddin Governorate

The Fatha Formation (Middle Miocene), formerly known as the Lower Fars Formation, is very important in the petroleum system. It may be an oil reservoir in many northern, central, and southern oilfields, in addition to being caprocks in Tertiary reservoirs. Based on cutting samples, the lithology of the formation was determined, as it consists of a sequence of limestone, marl, marly limestone, siltstone, anhydrite, or saltstone. The lower contact of the Fatha Formation is conformable with the Jeribe Formation, while the upper contact represents the outcrop. The lithofacies were divided into evaporite, marl, limestone, marly limestone, dolomite, and siltstone facies. Based on the petrographic study, the microfacies of the Fatha Formation were highly influenced by diagenetic processes. These included the processes of micritization, compaction, cementation, neomorphism, fractures, dissolution, dolomitization, and anhydrization, in addition to locally occurring authigenic minerals (pyrite). The microfacies analysis diagnosed four main microfacies: mudstone, wackestone, packstone, and grainstone, and four submicrofacies based on the prevailing grain types. According to the facies analysis results, the depositional environment of the Fatha Formation in the study area represents a shallow marine environment forming part of the inner ramp, including tidal flat, lagoon, and shoal.