PETROGRAPHY AND RESERVOIR EVALUATION OF KHEWRA SANDSTONE, UPPER INDUS BASIN, PAKISTAN

Abstract

The current research work is dealt with the sedimentological investigations, reservoir evaluation and surface to subsurface correlation of the Early Cambrain Khewra Sandstone exposed at the Khewra Gorge Eastern Salt Range. Lithologically, the Khewra Sandstone is mainly comprised of fine to medium grained, areneceous sandstone which at some intervals has silty clay bands and minor shale at the base. The results of petrographic analysis of Khewra Sandstone have revealed that the lithology of the Khewra Sandstone is quartz arenite and sub-litharenite according to Pettijohn (1973) classifications. The Khewra Sandstone has well sorted and rounded grains. According to Dickenson and Suzek (1979) and Dickinson (1985) provenance QFL diagram, the sandstone of the Khewra Formation at the study area is consistent with recycled orogeny and further it corresponds to the quartzose recycling of the recycled orogenic provenance. Based on the results of SEM analysis, the Khewra Formation has mainly intergranular porosity followed by microfractures porosity that enhance the reservoir efficacy of the formation. Surface samples passed through Helium Porosimeter test depict that the range of the porosity of 20 to 25% with average porosity of 22.6% and surface samples undergone through Gas permeameter test delineating permeability range of 439.17md to 1541 md averaging 1243 md. The Petrophysical analysis, in investigated wells of Rajian- 01 and Fimkassar-04 two zone is of interest in each well having (14 m and 45m) and (22 m and 24) thicknesses respectively. In Rajian-01, zone-01 has good reservoir properties having ranges of 10 to 15 % porosity and 10 to 15 md permeability, where in zone-02 has low values of porosity 7-9% and permeability 0.58md. The Zone-01 in Fimkassar- 04 permeability and porosity ranges of 4 to 6% and 1 to 3md whereas, in zone-02 have very low porosity 4% and permeability 0.12md respectively. So the porosity and permeability from outcrop and from borehole shows that the upper most part of Khewra Sandstone act as Reservoir.