Novel insights into the conventional and unconventional hydrocarbon potential of the Sembar Formation, Southern Indus Basin, Pakistan: A multi-analytical and basin modeling approach

Abstract

Significant hydrocarbon discoveries in the Southern Indus Basin of Pakistan are attributed to the Sembar Formation as the primary source rock. Prior studies on the Sembar shale were limited to screening analyses, which were inadequate for accurately evaluating its hydrocarbon potential. Therefore, this study employs a multi-analytical approach to assess organic matter’s impact on hydrocarbon generation by examining its quantity, quality, maturity, sources, and depositional paleoenvironment. The results reveal organic richness ranging from poor/fair to excellent, with total organic carbon varying from 0.51 to 28.12 wt%. The Sembar shale predominantly contains type III kerogen, with occasional type II and type IV presence. The biomarker results indicate a mixture of facies with varying contributions from higher plants, algae, plankton, and bacteria deposited in marine depositional settings that were predominantly suboxic and intermittently anoxic. The Sembar shale has reached the late mature stage, with vitrinite reflectance ranging from 1.11 to 1.40%. Basin modeling indicates a maximum transformation ratio of 72% in Jumman Shah-1 and 60% in Palari Sarki-1 for the Sembar shale. The detailed investigation suggests that the Sembar shale primarily generated conventional gas with a secondary contribution of oil. The abundance of quartz and kaolinite (analyzed through vibrational spectroscopy) in the Sembar shale supports its feasibility for fracturing. In conclusion, this study confirms the shale oil and shale gas potential of the Sembar Formation, demonstrating that integrating a multi-analytical and basin modeling approach provides a novel framework for assessing hydrocarbon potential and identifying sweet spots in the Sembar shale and analogous formations.