Fracture connectivity, porosity and permeability evaluation of the Sakesar Limestone around the Surghar Anticline, Kohat Plateau, Pakistan

Abstract

The ENE trending Surghar Anticline is located in the Surghar Range. Stratigraphy ranging in age from the Jurassic to EoceneIs nicely exposed in the Anticline. This thick sedimentary sequence is unconformably overlain by the fluvial molasses sediments of the Siwalik Group deposited during the Himalayan Orogeny. The Surghar Anticline exposes hydrocarbon bearing formations, which elsewhere are concealed by the younger sediments in the Kohat and Potwar foreland Basins. The potential reservoir rocks of the Sakesar Limestone of Eocene age are nicely exposed along northern and southern limbs of the Anticline. Detailed fracture analyses indicate that the formation is predominantly characterized by extension mode fractures followed by shear mode conjugate fractures. The ENE and NNW trending fracture sets are sub-parallel and orthogonal to the ENE trending Surghar Anticline axis respectively. Overall fracture density is greatest at the fore-limb than the back-limb. The fracture connectivity and porosity-permeability calculations demonstrate that various fractures at all stations within the formation are connected and imparting high secondary porosity and permeability.
These fractures could potentially provide pathways to hydrocarbon circulation to suitable trap structures.The prominent fracture network both geometrically and genetically related to the SurgharAnticline.