Evaluation of Selected Wells for the Mishrif Formation through Porosity and Saturation Study in the Ratawi Oilfield, Southern Iraq

The Mishrif Formation constitutes a significant oil reservoir within the Ratawi oilfield located in Southern Iraq. Three wells, R T-2, R T-3, and R T-5, situated 70 km northwest of Basra, were chosen to examine the petrophysical attributes with potential for oil production. Gamma-ray (GR), resistivity, and porosity logs were used to define the upper and lower parts of the Mishrif Formation. Water saturation of oil and non-oil areas, shale volume and porosity were calculated. The results show that the amount of oil shale is less than 15% in most wells, and the formation contains varying percentages of produced hydrocarbons. The Cretaceous Mishrif Formation is widespread in Iraq. Due to erosion, truncation, and lateral face changes, the thickness of this formation varies. The Mishrif Formation consists of four units from top to bottom: MA, CR-1, MB-1, and MB-2. The bottom of the Mishrif Formation (MB) extends from the Middle Mishrif, where the Middle Mishrif is at the top and the Rumaila Formation is at the bottom. This unit can be considered a cover rock for the Middle Mishrif Reservoir due to the low saturation rate in well 3, lower than the other wells in the two units, and the low saturation rate in the unit MB-2 in well 2. The results of analyzing and interpreting the MA unit records showed that they contain a very small percentage of the volume of oil shale in wells 5, 3, and 2, respectively, and the percentage of water saturation in wells was higher than in wells 3 and 5. CR unit is composed of a high percentage of shale or the volume of oil shale in well 2, followed by wells 3 and 5, considered the lowest percentage of oil shale. Analyzing and interpreting the logs showed they contain more water saturation in well 2 than in wells 3 and 5. MB unit can be found in all of the studied wells. The studied 3 wells have porosity ranges between 0.08 and 0.16 and water saturation ranges between 0.6 and 0.9.