Carbonate facies patterns of the Lutetian-Priabonian strata from the western Indian plate margin: Reservoir potential and palaeoclimatic implications

Abstract

The Lutetian–Priabonian (47.8–33.9 Ma) formations from the western Indian Plate margin (the Central Indus Basin of Pakistan) are investigated for reservoir potential assessment in the light of climatic implications using new well data based petrophysics combined with the statistical approach of cluster analysis. The electrofacies resulted from the distinctive patterns of the gamma ray (GR), sonic (DT), and density (RHOB) geophysical logs delineating carbonate reservoir heterogeneities across the study area. The Habib Rahi Limestone shows good reservoir intervals in the area. The findings suggest that the Lutetian–Priabonian Pirkoh and Habib Rahi Limestone are classified as class 3 (mud dominated) and class 2 (wackestone–packstone) type rock fabric based on the total porosity (φT) vs water saturation (Sw) cross plots, respectively. The study concludes eustatic dynamics as the dominant factor in controlling the carbonate deposition in the study area. Based on the investigated carbonates reservoir facies heterogeneity across the Central Indus Basin of Pakistan, it is proposed that the carbonates of Sulaiman Depression were likely deposited during major transgression-regression events, witnessing a climatic change from warmer in the Ypresian–Early Lutetian to cooler one in the Middle Lutetian to Priabonian. The depositional model proposed inner to middle shelf facies for the Pirkoh whereas middle to outer shelf slope facies for the Habib Rahi Limestone in the Central Indus Basin of Pakistan. The results of this study suggest that the carbonate reservoir heterogeneity occurrence in space and time may be traced to design a strategy for hydrocarbon exploration in the Central Indus Basin of Pakistan and in analogous settings around the world.