Experimental Investigation of Critical Parameters Controlling CH4-CO2 Exchange in Sedimentary CH4 Hydrates

Sequestration of CO2 in natural gas hydrate reservoirs may offer stable long-term deposition of a greenhouse gas while benefiting from CH4 gas production. In this paper, we review old and present new experimental studies of CH4-CO2 exchange in CH4 hydrate-bearing sandstone core plugs. CH4 hydrate was formed in Bentheim sandstone core plugs to prepare for subsequent lab-scale CH4 gas production by CO2 replacement. The effect of temperature, diffusion length, salinity, water saturation, CH4 hydrate saturation, and co-injection of chemicals (N-2 and monoethanolamine) with the injected CO2 were measured. The measurements prove the critical role of water saturation in these processes: formation of CO2 hydrate severely reduced the injectivity for water saturations above 0.1 fractions. The results presented in this paper are important when assessing natural gas hydrate reservoirs as candidates for CO2 injection with concurrent CH4 gas production.