Comparison of the Petrophysical Properties of the Zubair Formation in the Rumaila and West Qurna Oil Fields, Southern Iraq

The Early Cretaceous Zubair Formation is a key clastic reservoir in southern Iraq, but reservoir quality varies laterally between major fields. To evaluate and compare Zubair Formation petrophysical properties in the Rumaila and West Qurna oil fields and determine the main pay intervals and producibility. Open hole logs from four wells (RU145, R25, WQ1, WQ3) were quality checked, environmentally corrected, and interpreted using Interactive Petrophysics (IP v3.5). Shale volume was derived from gamma ray, lithology was identified using GR response, density–neutron crossover, PEF and crossplots, and porosity and fluid saturations were computed (including Indonesia watersaturation modeling). The formation is subdivided into upper, middle, and lower zones. Shale volume and carbonate content increase toward West Qurna, while effective porosity and hydrocarbon saturation improve toward Rumaila (highest in RU145). The middle sand member is the main pay zone, partitioned into reservoir units ZM1–ZM3 separated by barriers B1 and B2; West Qurna shows weak oil indications due to high shale and water saturation. Zubair Formation is producible in Rumaila, but largely nonproducible in West Qurna because increased shale and water saturation degrade porosity and permeability.