Microfacies analysis, depositional settings and reservoir investigation of Early Eocene Chorgali Formation exposed at Eastern Salt Range, Upper Indus Basin, Pakistan

The Early Eocene Chorgali Formation, Eastern Salt Range has been investigated for microfacies, depositional and reservoir analyses. The Formation consists of light to dark gray limestone with shale intercalations. The identified microfacies of Chorgali Formation are: (a) Foraminiferal bioclastic wackestone, (b) Benthonic foram-rich wackestone, (c) Bioclastic wacke-packestone, and (d) Miliolidal bioclastic wackestone. These microfacies represent wackestone depositional fabric with major faunal assemblage of Nummulites, Lockhartia, Assilina, and Miliolids. The environment of deposition is consistent with distal middle to proximal inner ramp settings. Diagenetically, the Chorgali Formation is affected by neomorphism, micritization, rare sparitization, dissolution, microfracturing, chemical and mechanical compactions and very rare dolomitization. Among these features, dissolution, micro-fracturing are the porosity-enhancing processes that increase the reservoir potentiality of the Chorgali Formation. The core plug porosity and permeability values of surface samples are 3.91% and 0.244 mD, respectively, depicting that surface sample porosities are comparatively lower than the subsurface porosities. The petrophysical analysis of the two wells (Balkassar-OXY-01 and Turkwal Deep-01) established that Eocene Chorgali Formation with dominant limestone facies at certain depths has suitable reservoir parameters. The Early Eocene Chorgali Formation of Pakistan depicts analogous features to that of the Early Eocene Naredi Formation (shale and carbonate member) of the Kutch Basin of Western India, based on the Nummulites and Assilina species, depositional fabric and depositional environment. This endeavor may be implied to the future studies of the Chorgali Formation as a hydrocarbon reservoir either in some unexplored oil or gas fields or to extend the limits of already explored fields along with the academic insights.