Study on the factors affecting the sealing performance and mechanical stability of CO2 hydrate cap during gas production from methane hydrate

Abstract An innovative idea of “reservoir reformation” was proposed earlier and verified to be feasible for enhancing methane gas recovery efficiency and CO2 sequestration by constructing an artificial impermeable CO2 hydrate cap between the methane hydrate reservoir and overburden. However, the effects of different factors on the sealing performance and mechanical stability of the CO2 hydrate cap need to be further clarified for the optimization of this new technology. In this study, experiments were conducted to simulate methane hydrate gas production by depressurization and analyze the influence of CO2 emulsion injection temperature, injection rate and overlying pressure by controlling these variables. The results indicated that the desired CO2 hydrate cap was formed by decreasing the injection temperature and rate. A cyclic process of “hydrate formation-fracture-regeneration” was proposed at a controlled injection rate of 3 mL/min. The degeneration rate of the CO2 hydrate layer was accelerated with an increase in the overlying pressure. The mechanical stability of CO2 hydrate cap was determined by the combined effects of methane hydrate decomposition and an increase of axial load.