Structural style in the central and southern part of the Kohat Basin and it's implication for hydrocarbon traps potential

Abstract

The Kohat Basin, located in the western Himalaya, is an active tectonic foreland basin with a well-developed and proven hydrocarbon system in north Pakistan. However, a significant portion of the basin remains relatively unexplored due to its complex structural style. This study integrates field investigation and remote sensing to map surface geologic features across different structural domains over an area of approximately 3000 km2. The subsurface 2D and 3D models uses MOVE standard rock properties with adjustment as per the lithologies of the rock units. The subsurface cross sections are restored using Fault block restoration to zero stratigraphic throw, unfolding and horizon flattening method in 3D module of the MOVE software. Hydrocarbon potential in terms of structural traps were conducted to evaluate the hydrocarbon potential of the study area through reservoir top interpolation in different regional structural transects. The basin is characterized by thrust tectonics, with distinct anticlines cored mostly by Eocene evaporites and broad synclines forming Siwalik Group rocks. The structural fabric within the basin trends predominantly east-west, resulting from the north-south directed tectonic stresses of the Himalayan collision. Tectonic deformation is most concentrated in three zones: the Manzalai anticlinorium, the Karak fault zone, the Karak anticline, and the Surghar Range thrust. Crustal shortening within the study area gradually decreases from the central part towards the margins, with regional sections AA’ stretching from Manzalai anticlinorium to Karak thrust, BB’ extending from Banda Daud Shah to Surghar thrust, CC’ from Makori to Surghar thrust, and DD’ spanning from Nashpa to Surghar thrust, showing shortening percentages of 6.6%, 15.1%, 10.3%, and 8.1% respectively. 3D block diagrams and subsurface contours of the reservoir rocks indicate promising structural traps for hydrocarbon accumulation. The Manzalai anticline, Karak fault zone, Karak anticline, and surrounding areas exhibit structural highs surrounded by structural lows, making them potential hydrocarbon kitchens.