Sedimentary Microfacies Analysis and Reservoir Characterization of the Middle Jurassic Carbonates: A Case Study from Lower Indus Basin, Pakistan

The present integrated study aims to study the sedimentary microfacies and reservoir characterization of the middle Jurassic carbonates (Chiltan Formation) succession exposed in lower Indus Basin, Pakistan. The plug porosity/permeability analysis and petrographic studies were carried out for the identification of facies and reservoir potential of the rock unit. The petrographic details show three microfacies in the rock unit including ooidal/peloidal grainstone microfacies, bioclastic grainstone microfacies and mudstone microfacies. The grainstone microfacies indicate deposition of carbonates in the high energy shallow inner shelf environment, while the mudstone microfacies indicate deposition in the restricted shelf environment. The visual porosity estimation shows the existence of secondary porosity in the form of minute fractures up to 7% and dissolution (vuggy) porosity up to 8%, while very low permeability is the characteristic of rock unit. This estimation is further supported by the plug porosity/permeability estimation that ranges from 0 to 11.5% porosity and 0–2.75 Ka Md permeability. The SEM also holds up the same interpretation and shows minute pore spaces between the grains. By integrating all the studies, it is concluded that the middle Jurassic carbonates of lower Indus Basin (Chiltan Formation) are poor-quality reservoir rock unit.