Evaluation of Shale Gas Reservoirs in Complex Structural Enclosures: A case study from Patala Formation in the Kohat-Potwar Plateau, Pakistan

Abstract Breakthroughs in shale gas exploration and production technology in China point to a possible solution to Pakistan's current energy crises. In this study, we evaluate the shale gas prospects in the Kohat-Potwar Plateau of Pakistan by establishing an integrated approach involving the analysis of fundamental elastic and petrophysical properties, Rock-Eval pyrolysis, and the sealing mechanism of shale. Detailed geochemical and petrophysical evaluation of the Patala Formation in the Kohat-Potwar Plateau indicates the good potential for shale gas with the following characteristics similar to the Longmaxi shale of Sichuan Basin China, i.e., (i) complex structural types sandwiched by tight limestone strata with low porosity (less than 3%), ultra-low permeability, high density, and large thickness which provides strong sealing capacity for gas preservation and enrichment; (ii) multiphase tectonic evolution of Patala Formation allowed various slippage processes to develop fractures and enhance the porosity and permeability; (iii) high organic matter content and thermal maturation stage (TOC > 2%, 416 to 445 °C); (iv) high brittle minerals content (e.g., calcite and dolomite > 40%); and (v) large formation thickness (> 30 m) at shallow burial depth