Shale gas potential evaluation based on well-logs and basin modeling of the Cretaceous-Paleocene succession of the Kohat Plateau, Pakistan: implication for shale gas exploration

This study examines subsurface data from three wells to assess the shale gas potential of the Cretaceous-Paleocene succession of the Kohat Plateau, Pakistan. The petrophysical analysis was performed to calculate total organic carbon (TOC) using the Passey model. Petro-elastic parameters (Poisson ratio, Young modulus, and brittleness) and thermal maturity were also evaluated, respectively. The average TOC values in Makori-01 (as calculated by Passey's method) are 2.88 (wt%) for the Lockhart Limestone and 2.10 (wt%) for the Chichali-1 Formation. In Manzalai-02 well, the Lockhart, Hangu, Kawagarh, Lumshiwal, and Chichali formations TOC values are 2.81 (wt%), 2.55 (wt%), 2.32(wt%), 2.29 (wt%) and 2.20 (wt%) respectively. To exploit the unconventional resources, zones I and II in the Sumari Deep X-01 well (Chichali Formation) with an average TOC value of 2.71 (wt%) can be considered favorable areas for further evaluation. The volume of shale value is resulted as maximum within Chichali Formation in Makori-01 (58.52–75.89%), Manzalai-02 (54.09%), and Sumari Deep X-01 (70.47%), while the least value is noted within Lockhart Limestone in Makori-01 (12.25%) and Manzalai-02 (14.02%), and in Hangu Formation in Sumari Deep X-01 (12.39%). Also, the elastic properties reveal two to four zones of Young modulus, brittleness index, and Poisson’s ratio within the Chichali Formation in the studied three wells. The isopach maps show that the Patala, Lockhart, Hangu, Lumshiwal, and Chichali formations in the research area exhibit variable thicknesses. The 1D maturity models of the Makori-01 and Manzalai-02 wells indicate burial to a depth of 8 km approximately 2.5 Ma ago and the apex of oil production (1.1% Ro). The 1D maturity models indicate that the Sumari Deep X-01 well has encountered minimal burial (in terms of both time and depth) and, as a result, exhibits minimal potential source rock intervals. The volumetric estimate of unconventional recoverable gas resources is approximately 1.57 TCF in the study area. The integrated research provides the basis for tracking and assessing the unconventional resource potential, distribution, and characteristics within the studied basin.