FACIES ANALYSIS AND RESERVOIR CHARACTERIZATION OF SEMBAR FORMATION, LOWER INDUS BASIN, PAKISTAN

Abstract

Pakistan petroliferous basin have vast area that remain unexplored. Independent international studies indicate that it has much more hydrocarbon potential than these proven reserves. Southern Indus Basin of Pakistan is considered sedimentary basin with immense hydrocarbon potential. The proven source rock in the Southern Indus Basin is the Sembar Formation which is being analyzed in this research study in terms of its hydrocarbon potential and facies analysis. Wireline log data of three wells and seismic lines of Gupchani area has been used for this. Sembar Formation has been divided into two main facies i.e sand and shale . Different lithological and mineralogical crossplots have been used for determining the type of lithology and clay mineral identification. The major part of the Sembar Formation is comprised of shale which is dominant in the lower part of the formation whereas the upper part is having sand facies in all the three (03) wells i.e Duljan-Re-Entry-01, Miran-01 and Shahdadpur-01. However, the top most sand facies decreases in thickness towards Shahdadpur-01 well moving from North to South direction. TOC values computed for the shales ranges between 1.5-2.5 wt% which lies in the fair to good source rock potential. However these shales are majorly composed of Illite and Kaolinite which are brittle clay minerals and are suitable for the frac job which is the most important criteria in evaluating the shlaes as a gas shale resource. Seismic data has been used to generate the subsurface structural trends in the area which shows planar to sub-vertical normal faults forming the horst and graben structures in the area due to extentional tectonics. Time and depth contour maps have been generated at the Sembar level in order to demarcate the depth of the Sembar and dipping trend in the area. The top most part of the Sembar Formation is mainly composed of sand facies so the possible lead marked on the contour map can be exploited for the hydrocarbon potential within the sand facies of the Sambar Formation. the faults do not penetrate up to the Chiltan Limestone and dies out with in the Sembar. This shows that the lower part which is mainly composed of shales might not be as much disturbed as the upper part. Moreover, the brittle clay minerals present within these shales are suitable for frac job but the sealing capacity of the faults has to be evaluated in order to exploit these shales as a gas shale resource for which high resolution seismic data is required.