Unconventional Lower Middle Jurassic Source Rock Evaluation Prospects in the Indus Basin, Pakistan: An Integrated Petrographic, Geochemical, and Maturity Modeling Investigation

Abstract

The fluvial-dominated deltaic to shallow marine depositional systems were studied by utilizing integrated approach of organic and inorganic geochemistry and petroleum system modeling (PSM). Employing an integrated approach encompassing through scanning electron microscopy (SEM), x-ray diffraction analysis (XRD), I D maturity modeling, vitrinite reflectance (VRr%), total organic contents (TOC%), and rock–eval analysis (RE), with techniques used for volumetric calculation in the current study, sheds light on the region's hydrocarbon generation potential. The TOC% in the Lower Jurassic rocks is 1.10%–7.45%, and in the Middle Jurassic, it is 1.06%–5.43%, having II and III kerogens from cross-plots, that is, RE temperature (T_max) versus productive index (PI) and T_max versus hydrogen index (HI). The VRr% is 0.97%–1.53%, demonstrating that the mature unconventional oil prospects and falls in oil-to-wet gas window. The PSM demonstrates that petroleum generation from the studied succession was started during the Late Cretaceous to Paleocene era for Jurassic and Cretaceous source rocks inferred from burial history, indicating the economic viability of unconventional prospect. Although the combined use of geochemistry and stratigraphy determined the values of the original old total organic contents (TOC_o, i.e., 2.39 and 1.69) and old HI (HI_o, i.e., 282 and 251) in the Upper Indus Basin (UIB) as well as TOC_o (3.07) with HI_o (625) in Lower Indus Basin (LIB) were used for the volumetric calculations. Besides the good values of TOC, TOC_o, kerogen subtypes, RE parameters, I D maturity modeling, and VRr%, the XRD and SEM analyses indicated good suitability for fracability under hydraulic stimulation. However, the oil shale potential of the studied strata shows a good correlation with the People's Republic of China, the United States (US), and Canada primarily based on criteria of depositional setting, TOC%, VRr%, and mineralogy. The key comparative indicators of oil shale potential in Indus Basin with international cases are TOC% >1, VRr% >0.6, and shale thickness >30 m with characteristics of mineral composition supportive of brittle features.