Role of Composition and Depth on Pore Attributes of Barakar Formation Gas Shales of Ib Valley, India, Using a Combination of Low-Pressure Sorption and Image Analysis

Pore characterization of shale has gained attention over the years because it provides a good estimate of the total storage capacity of a gas shale reservoir. Ib Valley is a potential shale gas reservoir in India, and this study is a systematic pore analysis of these Barakar Formation shales. A combination of low-pressure gas adsorption and high-resolution scanning electron microscopy coupled with image analysis was used to characterize the pore structure and pore size distribution. The changes in pore attributes with increasing depth, varying mineral composition, and organic matter content were established. We observed a steady decrease in the micropore volume and carbon content with depth. We could successfully segregate the organic matter pores and inter- and intraparticle pores using the scanned images. Both CO2 and N-2 adsorption experiments indicate high adsorption and, thereby, good gas storage capacity in the shales from shallower depth. The decrease in the micropore volume with depth may be related to higher compaction and reduced organic carbon content. From a fundamental point of view, the CO2 grand canonical Monte Carlo model shows better fitting in calculation of the pore size distribution compared to the CO2 density functional theory model.