Well Logs and Petrophysical Characteristics of the Hartha Formation at Balad Oil Field, Central Iraq

The Hartha Formation is a crucial oil production reservoir in southern and central Iraq; known for its diverse carbonate sediments. The Hartha Formation at Balad oil field is divided into upper and lower parts. Based on the petrophysical characteristics (resistivity, porosity, and saturation), the lower parts of the Hartha Formation that contain the hydrocarbons are divided into two units: Har.UA and Har. UB. Analysis using the M-N cross-plot showed that calcite is the predominant mineral in the Hartha Formation, with dolomite and shale occurring to a lesser extent. Additionally, the neutron vs. density cross-plot analysis reveals that the Hartha Formation is primarily composed of limestone with dolomite as a secondary component. Based on the ComputerProcessing Interpretation (CPI) analysis of five wells studied at the Balad oil field, the wells in the northeastern block (Ba-5, Ba-6, and Ba-7) exhibit favorable reservoir quality. These wells are characterized by higher porosity fractions (0.228, 0.215, and 0.224), lower water saturation fractions (0.093, 0.099, and 0.092), and higher hydrocarbon saturation fractions (0.906, 0.9004, 0.907). Based on the separation of neutron and density records, these wells contain oil and gas phases, especially wells (Ba-6 and Ba-7). On the other hand, the wells located in the graben area (Ba-1 and Ba-8) demonstrate lower reservoir quality with porosity fractions of (0.13 and 0.20), water saturation fractions of (0.347 and 0.257), and hydrocarbon saturation fractions of (0.652 and 0.708), show only a single phase, specifically an oil zone.