Structural Modeling and Restoration To Analyze Source Rock Maturity Southeastern Potwar Basin, Pakistan

Abstract

The Potwar Basin in Pakistan, a prominent segment of the Himalayan foreland fold-and-thrust belt, is a major hydrocarbon province characterized by intense compressional tectonics and complex subsurface geometries. The Kal Oil Field is located within the highly deformed eastern Potwar, featuring numerous structural traps, primarily formed by stacked thrust sheets and associated folding hosted by complex interaction of Domeli and Dil Jabba Thrusts. This primary objective of the study is to understand and map the subsurface geometries and their architecture in order to understand the distribution and interactions of different petroleum traps present in the study area followed by petrophysical analysis to asses source rock maturity. The methodology involves two main stages: First, detailed structural interpretation of 2D and seismic reflection data, integrated with well-log information, is performed to define the geometry, kinematics, and interaction of the major thrust faults and associated fold structures. Second, petrophysical analysis, particularly Vitrinite Reflectance measurements from wells in the upper thrust sheets, is used to constrain the present-day thermal conditions. Third, the structurally restored model is used as the basis for dynamic basin modeling. Detail Seismic interpretation followed by mapping (TWT, DEPTH) of subsurface geometries confirms the moderate to extreme compression conditions are prevailing in the study area, Since the structural geometries are varying from common imbricated associated folds to stacked thrust sheet providing multiple sites for hydrocarbon exploration. The replication of salt range formation and clays of Murree Formation supports the effective sealing of these traps. The secondary faults present in each sheet can be suitable venues for hydrocarbon migration. The structural interpretation of the Kal area reveals multiple stacked sheets, with the top sheet of the Kussak Formation (drilled in Kal-01 and Saba-01 wells) exhibiting good source rock potential. TOC and Vitrinite Reflectance values indicate that these shales fall within the oil generation window. With increasing burial depth, the lower sheets of the Cambrian strata are likely subjected to higher temperature and pressure, enhancing thermal maturity and potentially reaching the gas generation window. Consequently, structural closures within these deeper sheets may serve as potential gas reservoirs. In the Kal area, the Kussak Formation shales also show fair to good source rock potential within the oil window, with an average TOC of 1.44% and Vitrinite Reflectance of 1.50.