Evaluation of shale gas potential in the Lower Cretaceous Sembar Formation, the Southern Indus Basin, Pakistan

The Lower Indus Basin of Pakistan is reported to contain significant recoverable resources of shale oil, but until now no detailed research has been done to estimate its shale gas potential. In this study, an integrated approach was proposed and applied, combining source rock screening (SRS), petroleum system modeling (PSM) and volumetric calculations to evaluate the shale gas potential of the Lower Cretaceous Sembar Formation, the Southern Indus Basin. The study was conducted based on the data from the public domain of petroleum industry in Pakistan, including vertical well sections, well logs, seismic sections, regional geological sections, base maps, and geochemical data. Results of source rock screening (SRS) found that the organic-rich shales of the Sembar Formation have %Ro (vitrinite reflectance) ranging from 0.76 to 3.79 (corresponding to TAI from 2.8 to 2.9), kerogen types ranging from type II to type III, and TOC (total organic carbon) values as high as 9.5%. Results of petroleum system modeling (PSM) indicated that shales of the Sembar Formation are in the thermal window for gas and oil generation. Hydrocarbon generation was found to have started in the Late Cretaceous with maximum burial in the Late Paleogene. Shales of the Sembar Formation are interpreted to be over-pressured at present. Finally, the volumetric calculation estimated that the volume of Retained Gas In Shale (RGIS) of the Sembar Formation is 359 Trillion Cubic feet (Tcf), out of which 43.1 Trillion Cubic feet (Tcf) is risked RGIS. The results of this study concluded that the Sembar Formation has momentous shale gas potential and the integrated approach employed in this study for shale gas potential evaluation is pertinent to evaluate source rocks in other sedimentary basins of Pakistan.