The Impact of Diagenesis and Dolomitization on the Reservoir Potential of Middle Jurassic Samana Suk Formation from Khanpur Dam Section Hazara Basin, Khyber Pakhtunkhwa Pakistan

Abstract

Detailed study of the Samana Suk Formation has been carried out from the Khanpur Dam Section. Two
lithological units have been identified in the studied section, limestone and dolomite (60% and 40% respectively). The
dolomite is present in the form of beds or veins filling fracture and joints. In the field three types of dolomitization can
be observed, yellowish, brown and saddle varieties. Microscopic studies reveal either partial, complete and selective
dolomitization, which include (1) fine crystalline planar-euhedral, subhedral dolomite and non-planer anhedral
dolomites (2) fine to medium crystalline non-planar-anhedral dolomite, (3) medium crystalline planar-euhedral
dolomite, (4) coarse crystalline planar-subhedral dolomite, (5) coarse crystalline non-planar-Anhedral dolomite and (6)
saddle dolomites. The dolomitic facies have intercrystalline porosity compared to limestone facies, which is
characterized by inter-particles, moldic, vug, intraparticle, fractures and burrows porosities. The porosity of the
limestone facies varies between 3% and 6%, which increase to 12% in the fractured samples, while the porosity of the
dolomitic facies is in the range of7% and 14%. It has been concluded that the increasing porosity is the direct result of
dolomitization. This interpretation is consistent with the field and petrographic observation, which indicate that
dolomitization is secondary in nature. The dolomitization is the direct result of fluid along the fault plane due to
tectonic loading creating pressure gradient.
Keywords: Samana Suk Formation, diagenesis, dolomitization, Hazara basin, porosity analysis.