Petrophysical Evaluation of the Zubair Formation in the Luhais Oil field, Southern Iraq

This study analyses borehole log data from five producing wells to determine the petrophysical characteristics of the Zubair Formation in the Luhais Oil Field. This research aims to assess the mineralogical and lithological origin of the reservoir, calculate important petrophysical parameters, and evaluate reservoir units across various stratigraphic members. The NPHI-RHOB cross plot shown that sandstone is the primary lithological composition, while M-N plots which confirmed quartz dominance, revealing a sandy-clastic reservoir. Key parameters including shale volume, effective porosity, permeability, water saturation, and net pay thickness were all calculated using Computer Processed Interpretation (CPI). The Zubair Formation was divided into three members: the upper (Sandstone-Shale), which was further subdivided into six reservoir units (A-F), the Middle (Sandstone), and the lower (Shale-Sandstone). The evaluation results showed that unit C represents the production interval, with significant net pay thicknesses and attractive reservoir characteristics, whereas unit E has limited reservoir quality. Units A and B have weak properties, while units D and F are non-reservoir intervals. The findings also revealed that the middle and lower members’ contributions to the study area are limited due to high water content and poor reservoir continuity, with penetration observed in only two of the wells investigated.