Organic Geochemical Evaluation of the Lower Cretaceous Sembar Formation to Identify Shale-Gas Potential from the Southern Indus Basin Pakistan

: In this research, we evaluated the shale gas potential of Sembar Formation (Lower Cretaceous) from four different wells, i.e., Well TE-1, Well TE-2, Well TE-3, and Well TE-4 of the Southern Indus Basin, Pakistan. Seventy-eight samples have been analyzed for this study by means of Total Organic Carbon (TOC), Rock-Eval analysis, Vitrinite Reflectance (Rₒ), and Geochemical logs. The Lower Cretaceous Sembar Formation in the study area is mainly composed of shales and minor traces of siltstone and sandstone. Sembar Formation in the Southern Indus Basin is organically rich with an average TOC of (2.05 wt. %). The shales of Sembar Formation has adequate potential to generate hydrocarbons. The mean genetic potential is 4.69 mg HC/g rock. The HI values range from 5.96-505 mg HC/g TOC with an average value of 144.45 mg HC/g TOC. Whereas, the OI values range from 3.90-306.66 mg CO₂/g TOC with an average value of 45.43 mg CO₂/g TOC. The Hydrogen Index data, HI vs. Tmax cross plot, and Van krevelen Diagram (HI vs. OI) show the Sembar Formation has type II & type III kerogen, which are mainly oil and gas prone. Organic-rich shales of the Lower Cretaceous Sembar Formation in the Southern Indus Basin are thermally mature. The average Tmax values are (450 ºC), the mean Production Index is 0.38, whereas the calculated Vitrinite Reflectance based on burial history is 1.5 (%). On the basis of current investigations, it is concluded that sufficient vertical thickness of organic-rich facies, their lateral continuity, High TOC content, appropriate Kerogen type, thermal maturity reflecting oil– gas generation zone, an indigenous hydrocarbon exists within the Formation. Thus the Sembar Formation has the potential to produce unconventional hydrocarbons in the Southern Indus Basin.