Effects of pressure and temperature conditions on thermodynamic and kinetic guest exchange behaviors of CH4 - CO2 + N-2 replacement for energy recovery and greenhouse gas storage

Abstract

Both natural gas production and CO2 sequestration can be simultaneously achieved in natural gas hydrates (NGHs) by using a guest swapping technique. In this study, the effects of replacement pressure (10.0-18.5 MPa) and temperature (274.2-277.2 K) conditions on the guest exchange behaviors of CH4 - CO2 + N-2 replacement were investigated, focusing on the extent of replacement and replacement kinetics. At 274.2 K, the extent of replacement increased with injection pressure of CO2 (20%) + N-2 (80%) gas, which is mainly attributed to a larger N-2 inclusion at a higher pressure. At a higher temperature, the extent of replacement did not change, but CO2/N-2 ratio in the replaced hydrates decreased slightly. An increase in the pressure led to an accelerated CO2 inclusion rate in the large (5(12)6(2)) cages at the initial stage and an enhanced N-2 inclusion in the small (5(12)) cages at the final stage. The enhanced replacement kinetics at a higher temperature is attributable to the increased inclusion rates of both CO2 and N-2 at the initial stage of replacement. The results provide valuable insights into the guest swapping mechanism of CH4 - CO2 + N-2 replacement occurring in NGH reservoirs with various locations and environments. (C) 2021 Elsevier Ltd. All rights reserved.