Structural and stratigraphic controls on reservoir distribution in the Ptah oil field, Shushan Basin, North Western Desert, Egypt

Abstract

Abstract The Ptah Oil Field, located along the northwestern margin of the Shushan Basin in Egypt’s Western Desert, hosts structurally complex clastic reservoirs whose hydrocarbon distribution is strongly fault controlled. This study applies an integrated seismic–petrophysical–petrographic workflow to characterize reservoir architecture and trapping mechanisms within the Bahariya, Lower Cretaceous Alam El Bueib (AEB-3D/3E) and Paleozoic Shiffah B sandstone intervals. Interpretation of 20 two-dimensional (2D) seismic lines extracted from 3D seismic cube, calibrated with well logs and core from six wells, reveals an extensional fault framework dominated by NW–SE and E–W normal faults forming horst–graben geometries and three-way dip closures that govern reservoir preservation and compartmentalization. Petrophysical analysis indicates moderate reservoir quality with significant lateral variability in reservoir properties. The net pay thickness varies across the study area and reached to 13, 38 and 129 ft. for Bahariya, Alam El Bueib and Paleozoic Shiffah B Sandstone reservoirs. Effective porosity derived from well logs ranges approximately between 7–12%, while core measurements indicate porosity values reaching 21%. Permeability values obtained from core analysis vary widely between 0.02 and 839 mD, reflecting heterogeneous pore systems within the sandstone reservoirs. Structural mapping identifies several fault-bounded closures with aerial extents ranging from approximately 273 to 4500 acres across the studied stratigraphic intervals, these structural configurations may represent promising exploration targets, particularly where fault sealing and reservoir quality are favorable. Petrographic observations confirm that diagenetic clay distribution further controls pore structure and permeability. Integrated results demonstrate that hydrocarbon accumulation is primarily dictated by the interaction of fault architecture, stratigraphic preservation, and diagenetic modification rather than reservoir properties alone. This framework refines reservoir delineation, reduces exploration uncertainty, and identifies structurally favorable targets, providing a transferable methodology for evaluating fault-controlled clastic reservoirs in extensional basin settings.