Reservoir Characteristic of Sa’adi Formation, Southern Iraq

The Sa’adi Formation (Santonian-Campanian) is one of the important reservoirs hydrocarbon-bearing zones in the southern Iraq. According to the reservoir quality, the Sa’adi reservoir is considered a clean tight reservoir (moderate to low permeability less than 20 mD) in all study area. The Sa’adi Formation subdivided into two members; the upper member is chalky limestone rocks and the lower member is limestone, the lower member can be further divided clearly into three units (A, B, and C) according to wells logs. Petrophysical properties showed a relationship with facies distribution, the relationship between porosity and permeability in some study wells through Winland R35 method, four types of pore throat sizes have been identified (nanopores, micropores, mesopores, and macropores). Upper Sa’adi and lower Sa’adi Unit C have the low quality related to medium average values of porosity less than 12% and permeability less than 2mD while it’s absence of oil saturation. The micropores and nanopores dominate of this flow and related to mud-supported microfacies of outer ramp and mid-ramp facies associations. While lower Sa’adi Unit A and B, mesopores and macropores marked with grain-support facies related to inner-ramp facies associations, which reflect to high porosity is 17% and medium permeability less than 20 mD with high oil saturation at (78–65%), it represents the best flow unit of Sa’adi Formation in West Qurna I and West Qurna II Oilfields.