Organic geochemistry indicates source-rock characteristics and hydrocarbon potential: A case study from Early Cretaceous Sembar Formation, southern Indus Basin, Pakistan

Abstract

Shale samples from the Early Cretaceous Sembar Formation were selected from a well in the southern Indus Basin, Pakistan, and were analyzed for geochemical parameters. The study investigates the source-rock characteristics and hydrocarbon-generation potential indicated by organic richness, organic-matter type, and thermal maturity. The high values of total organic carbon (TOC) content of the Sembar shales indicate favorable source-rock characteristics. The shale samples analyzed in this study have hydrogen index (HI) values in the range 43–238 mg HC/g TOC and oxygen index (OI) values in the range 14–151 mg CO2/g TOC. Accordingly, the organic matter is mainly type III, which is consistent with high amounts of terrestrial organic matter. The dominant presence of type III kerogen suggests mainly gas generation. According to geochemical-maturity indicators, the organic matter in the analyzed Sembar shale is thermally mature, having reached an early peak-window, but commercial amounts of oil and/or gas have not yet been generated. Therefore, further petroleum exploration at depth in the southern Indus Basin, mainly for gas production, is recommended.