A Comparative Study on the Pore Size Distribution of Different Indian Shale Gas Reservoirs for Gas Production and Potential CO2 Sequestration

A thorough knowledge on pore size distribution (PSD) is one of the fundamental requirements for characterization of shale gas reservoirs and for accurate estimation of their gas storage potential. However, being an important future source of energy need in India, the pore size distribution of Indian shale gas systems is not scientifically well understood. In the present study, the nanoscale pore size distributions of prospective Indian shale basins, viz., Cambay, Cauvery, Krishna Godavari (K-G), and Damodar valley (DV), were investigated using mercury injection porosimetry (MIP) and low-pressure gas adsorption (LP-N-2 and LP-CO2) techniques. The study focused on identifying the priority basins for shale gas production which can be substituted for sequestration of CO2 based on their PSDs. The samples exhibited higher thermal maturity with increasing organic content. The chemical composition of the shale samples was inferred from XRD data, which depicted higher clay content. The prominent clay minerals identified muscovite, illite, and kaolinite, which are generally flaky in nature. These minerals contributed significantly to the pore size complexity of the studied shale samples. The experimental result suggested that the samples exhibited diversified pore size characteristics. The shales are chiefly bimodal, consisting of mesopores (2-50 nm) and micropores (<2 nm). The micropores were efficiently accessed using CO2, while N-2 was effective on characterizing the mesopore region. MIP analysis was used to infer the pore throat area. The average pore diameter of samples ranged from 3.38 nm in Damodar valley to 3.94 nm in thr K-G basin, while Cauvery and Cambay basin samples possessed 3.88 and 3.86 nm, respectively. Both N-2 and CO2 adsorption (type II and type I, respectively) suggested the presence of micropore infilling in all of the basin samples. However, Cauvery basin samples were inferred with higher mesopore content as compared to other basins and possessed higher quartz percentage, making it more appropriate for hydraulic fracturing. The Cauvery basin showed enrichment of larger pore sizes. The results signified that the Damodar valley shales have a higher affinity toward CO2 adsorption. This suggested that the basin could be a better host for future carbon storage, compared to other basin pore structures.