EFFECT OF COMPACTION ON POROSITY AND PRESSURE OF RESERVOIR AND NON-RESERVOIR FORMATIONS OF TERTIARY AGE IN BALKASSAR AREA, POTWAR, PAKISTAN

Abstract

Compaction is a process in which the sediments, which were deposited earlier, are buried under the sediments which are deposited later. It is one of the major component which controls the porosity and reservoir pressures. The basic idea of this study is to analyze the effect of compaction on the porosity and pressure in the reservoir and nonreservoir formations of tertiary age in Balkassar area, Upper Indus Basin. 3D seismic cube (10 km2) and three wells of Balkassar block are used for this analysis. In order to determine the effects of compaction on the porosity and pressure in Balkassar area, porosity has been computed from the log data and seismic data as well. The results of the both the data sets are giving good porosity values in Chorgali Formation ranging between 10-12% and in Sakesar Limestone porosity values are between 2-3%. Pore Pressure in Balkassar OXY 1 well have also been computed using two different software and the results of both validate each other. Underpressure conditions in the Chorgali Formation, negatives pressures in Sakesar Limestone and several overpressure zones in the Murree Formation. Burial history plots are generated for the Chorgali and Sakesar formations to analyze the porosity reduction rate, with respect to lithostatic pressure, pore pressure and average porosities. the limestone of the Eocene age which were deposited before the collision of Indian plate had enough time for fluid expulsion and show underpressure conditions with high porosities. Whereas, Murree Formation shows overpressure zones due to high rate of sedimentation during the Miocene age which restricted the process of fluid expulsion from the pore spaces and shows high porosity values.