Microfacies Analysis And Reservoir Characterization Of Early Eocene (Ypresian) Sakesar Limestone In The Eastern And Central Salt Range, Upper Indus Basin, Pakistan

Abstract

Detailed investigations have been carried out for the Early Eocene Sakesar Limestone to evaluate microfacies analysis, reservoir characterization and depositional environment. This work is accomplished of three outcrop sections which are, Dandot village section, Ratucha village section and Sardhai village section in Eastern and Central Salt Range Potwar plateau, Upper Indus Basin. In addition, well-cuttings of Sakesar Limestone were studied from Balkassar-7 well located in the Potwar sub-basin. The main aim of this research work was to investigate the reservoir quality and identify the microfacies of Sakesar Limestone. Based on the relative proportions of bioclasts and micrite, five microfacies were identified which include Calcareous Algal-Miliolidal wackestone, Alveolina-Miliolidal packestone, Assilina Nummulitic wackestone, Lokhartia Rich-Foraminiferal wackestone and Nummulitic Heterostegina packestone. The presence of micrite matrix, relative abundance of fossils and their association in these microfacies has proved that the Sakesar Limestone to be deposited in Shallow-marine, inner-middle ramp environment. The porosity types identified in Sakesar Limestone include fracture, moldic, interparticle and intraparticle porosity. The visually estimated porosity values of Sakesar Limestone from thin-section studies ranges from 0.70% to 2.9% while the core plug porosity and permeability values of the outcrop samples vary between 0.66% to 2.98% and 0.05mD to 0.09mD respectively. The well-cuttings plug porosity values ranges from 0.79% to 2.60% and permeability from 0.06mD to 0.44mD respectively. The relationship between plug porosity and permeability shows a reasonable correlation coefficient. The main reservoir quality enhancement factors are fractures on outcrop scale while microfractures and dissolution on microscopic scale which makes the Sakesar Limestone as a secondary reservoir in nature.