THE ROLE OF THE SALT TECTONIC FOR PETROLEUM SYSTEM DEVELOPMENT IN EASTERN POTWAR SUB-BASIN, PAKISTAN

Abstract

The geological structures and seismology of Northern Pakistan are affected by salt tectonics. These salts or evaporates are the major contributor, which are balancing northward thrusting and south verging uplifts in this part of Sub Himalaya i.e., in back bulge. Also, the role of basements related normal faults is important, which are forming ramp-flat geometries where these incompetent strata (evaporites) are assembled and give rise to popup structures like Balkassar, Joya Mir, Chak Nourang and diaprism like Salt Range Thrust (SRT) in the southern part. The Study is lies in the back bulge of the Sub Himalaya or in the southern part of Potwar platform sequence. Balkassar and Salt Range structures are evaluated to know the behavior of the salt in Structure development where popups and diaprism is prominent. Basement faults under these structures are almost running in EW direction and assembling the maximum thickness of salts even it exceeds from its actual thickness (800-1000 m). This study is an attempt to investigate the role of salt in the geological deformation of the Salt Range-Potwar Plateau using well log interpretation, Burial history of wells and seismic interpretations, seismic data facilitate to construct the sub-surface models of the study area i.e., Kalar Kahar and Balkassar area. The structural restoration practice was done alone seismic lines (KK-13 and PBJ-1) to calculate difference appeared due to the shortening. Areal distance of the two seismic lines (tied with jump tie method & well log) is 43 km but when it is restored in a form of platform sequence the distance is 78 km. Therefore, difference or shortening of about 35 km. Burial history shows composite unconformity from the top of Cambrian to Lower Permian and again remained exposed from middle Permian to Middle Paleocene age. Temperature data shows increasing temperature and pressures with respect to depth i.e., 2 degrees per 100 m. Sonic/density log also gives compaction trend with respect to the depth but it falls dramatically in the evaporites due to the very low competency i.e., from maximum 2.9 g/cm3 of dolomite to salt about 1.1 g/cm3. While talking about the reservoirs and hydrocarbon prospectively, Khewra Sandstone has very good results. But not producing in the whole basin because of the presence of sealing strike slip fault in Balkassar structure.