Sedimentary facies, diagenetic analysis, and sequence stratigraphic control on reservoir evaluation of eocene sakesar limestone, upper indus basin, NW himalayas

Abstract

The tectonic deformation by the Himalayan orogeny resulted in the development of sedimentary basins with multiple petroleum plays, especially in the Eocene rocks. Previous studies on the Eocene rocks broadly discusses the depositional environment, diagenesis, and outcrop features. However, the present work includes both outcrop and wireline log data to elucidate microfacies, diagenetic control, and sequence stratigraphic patterns used for reservoir characterization of the Sakesar Limestone, both at surface and sub-surface level. Field features include light to medium grey, massive, nodular, fossiliferous, fractured limestone which is mainly classified into wackestone to packstone microfacies. Several diagenetic features such as cementation, neomorphism, compaction, and calcite-filled fractures are observed and they have reduced the pore network. However, secondary dissolution in the bioclastic wackestone facies and fracturing have enhanced the pore network and its connectivity. Wireline logs also show sonic porosity of 5.3%, and 3.16% effective porosity is sufficient for carbonate reservoirs. The bulk porosity may reach up to 14%. Sequence stratigraphic study show that coarsening upward and massive carbonate beds characterized by packstone faices are interpreted as highstand systems tract in the Sakesar Limestone, which suggests the prograding depositional pattern. The outcome of this work demonstrates that potential reservoir intervals in the Sakesar Limestone are mainly fractures and solution enhanced pore spaces in the wackestone microfacies which can be targeted for enhancement for the exploration and production in these carbonate rocks .