Improved diagnosis of the carbonate reservoirs: a case study from the Potwar Basin, northwest Pakistan

Abstract

The key obstacles to developing the four wells in the Pariwali Block of the Potwar Basin in Pakistan continue to be an accurate age diagnosis of the reservoir intervals, facies variation, and locating the hydrocarbon target for future development wells. The purpose of this work is to offer integrated biostratigraphic, facies, and sequence stratigraphic information from well cuttings to more fully characterize the carbonate reservoirs. The diagnosis of exact stratigraphic units, their ages, and order of cyclicity were constrained by larger benthic foraminiferal biostratigraphy, and the facies integration has made it possible to identify the sequence stratigraphic architecture. The Paleogene Lockhart, Sakesar, and Chorgali Formations were diagnosed, which were deposited on a ramp carbonate platform in a range of environments, including tidal flats, the inner ramp, the proximal middle ramp, and the outer ramp. Integrated sequence stratigraphic analysis has demarcated two third-order cycles (TR1 and TR2), two depositional Sequences (Sequence 1 and Sequence 2) having two transgressive systems tracts (TST 1 and TST 2) which are separated from the Two regressive Systems tracts (RST 1 and RST 2) by Maximum Flooding Surfaces (MFS 1 and MFS 2), respectively. The diagenetic analysis and nanoporosity information was helpful in delineating sweet spots for the hydrocarbons in the Lockhart, Sakesar, and Chorgali formation that lies within the larger benthic foraminiferal–algal wackestone–packstone and dolomitized mudstone–wackestone facies. The occurrence of lime mudstone facies controlled the reservoir compartmentalization at repeated intervals in different wells.