Evaluation Of Paleoenvironment, Reservoir Characterization, Microfacies And Diagenetic Fabrics Of Eocene Sakesar Limestone Western Salt Range, Upper Indus Basin, Pakistan

Abstract

In the western Salt Range (Nammal George) and Balkassar Oil field (Balkassar POL-1 and OXY-2), Eocene Sakesar Limestone has been investigated for the Evaluation of Paleoenvironment, reservoir characterization, microfacies analysis, and diagenetic fabric. The research work was carried out for the outcrop samples, picked from the Sakesar Limestone of the western Salt Range and two wells selected in the Balkassar Oil field (Balkassar POL-1 and OXY-2) Potwar Plateau, district Chakwal, Pakistan. Twenty-eight (28) outcrop samples of Sakesar Limestone were collected from Nammal George. The microscopic study revealed three microfacies and six (6) sub-microfacies with distinct textures, fossil content, and allochem types. These microfacies are Wackestone Microfacies, Mud-Wackstone Microfacies, Mudstone Microfacies, and sub microfacies are uniserial foraminifer, Lockhartia species, dasycladacean algae, bioclasts, milliolids, and Ranikothalia sub-microfacies. On the basis of the presence of biota, and micritic matrix in various microfacies, the Sakesar Limestone is interpreted to be deposited in the inner to middle shelf settings. In the western Salt Range, Sakesar Limestone has been affected and modified through various diagenetic events. The diagenetic fabrics includes the stylolites, calcite-filled microfracture, aragonite to calcite transformation, micritization, cementation, neomorphic, mechanical compaction and chemical compaction. Six (6) samples were selected from the outcrop samples for the permeability and porosity tests, carried out in the Hydrocarbon Development Institute of Pakistan (HDIP), ranging from 3.15% to 19.49% and 0.021 to 0.117 milli darcy respectively. Rock porosity and permeability were affected by the depositional, diagenetic and informational processes. The used data for Petrophysical analysis is obtained from Landmark Resources (LMKR) with the approval of the Directorate General of Petroleum Concession (DGPC). The petrophysical analysis for Balkassar POL-1 and OXY-2 is carried out by using geographic software and gamma-ray, sonic, caliper, neutron, density, and resistivity logs were used to identify the subsurface lithology of the Sakesar Limestone. While the paleoenvironment is recognized by the identification of cylindrical shapes in the gamma-ray log curve. The Surface (3.15 to 19.49) porosity and subsurface porosity for Balkassar POL-1(9.8%) and Balkassar OXY-2 (1.92) is correlated, clearly suggesting that the surface porosity is higher and subsurface is lower which may be due to overburden pressure