Specific surface area and pore size distribution in gas shales of Raniganj Basin, India

Abstract

Understanding of multiscale transports of shale gas is important for shale gas exploration and exploitation. Traditional porosity determining approaches normally underrate the shale gas transport capacity as these techniques do not include adsorb gas in nanometer-sized slit pores. Silty shale, carbonaceous shale, claystone and ironstone shale unit of Barren Measures Formation was examined to understand the pore system at various scales. The pores are intergranular, intragranular, interlayer, dissolved pore and fracture pores where gas molecules are present as free state and/or adsorbed gas in the internal structure of the pores and at the edge of their structures. Here, we used the Brunauer–Emmett–Teller technique with scanning electron microscopy for considering the adsorption mechanism to understand the gas transport in micro and nano pores in shales. The adsorption parameters between organic wall and grain surface were observed to be controlled by clay mineralogy. SEM, X-ray diffraction and BET manifest significant information about role of clays, organic matter and mineral composition in development of pore network, which also governs the gas storage and transport properties. A large portion of pores in Barren Measures shales ranges between 20 and 55 nm and the pore size diameter ranges from 5.49 to 29.75 nm.