Quantification of CH4 adsorption capacity in kerogen-rich reservoir shales: An experimental investigation and molecular dynamic simulation

Abstract

Kerogen coexisting with inorganic matter has a complex nanoscale pore structure, including intra-kerogen pores (IKNs) and inter-particle pores between kerogen and inorganic matter (IPNs), which has made it difficult to accurately evaluate shale gas reserves and production. In this study, we examine how IKNs and IPNs contribute to shale gas adsorption via experiments and molecular simulations. To distinguish the effects of IKNs and IPNs on CH4 adsorption, a programming-heating method was devised to burn out the organic matter from shale samples without destroying inorganic matter by carefully controlling the temperature. The burned organic matter was replaced with carbon nanotubes and graphite particles to represent the IPNs and IKNs. Our experiments show that the adsorption capacity of the samples with IKNs can reach 2.187 mg/g, while the samples with IPNs on their surface area possess an adsorption capacity of only 0.974 mg/g. Even through organic matter only accounts for approximately 3.06% of the total weight of shale, it provides at most 67.4% of the total adsorption sites for CH4. The results of CH4 adsorption were verified using simulations of molecular dynamics. This study provides a quantitative approach to understanding and characterizing the mechanism of CH4 adsorption in shale kerogens.