Conclusions

The experimental results of CO2 sequestration in CH4 hydrate reservoirs and subsequent CH4 recovery (under excess gas conditions) were obtained by using two types of experimental set ups. The experimental investigation using the Ultrasonic Rig imitated CO2 injection in a methane hydrate reservoir under excess gas conditions. An increase in CH4 composition in the headspace gas samples indicates that CH4 enclathrated in the host hydrate lattice was partially replaced by the injected CO2. Injection of CO2 below its saturation pressure in this test produced 7.97-mole% methane in 206 hours. The experimental results show that the CH4 recovery rate in porous media was higher than previous results obtained by Hirohama et al. (1996) under bulk conditions.

The tests in the Visual Glass Micromodel showed that CO2 injection into sediments containing methane hydrates under excess water conditions was converted into either CO2 hydrates or mixed CO2-CH4 hydrates. However, it should be noted that these tests were conducted under constant temperature conditions, which may not be the case in real reservoirs due to the release of heat as a result of CO2 and/or mixed CH4- CO2 hydrate formation.

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