Methane hydrate (CH4 hydrate) consists of cagelike crystal structures made up of hydrogen-bonded water molecules surrounding guest molecules of CH4. CH4 hydrate existing in marine sediments is anticipated to be a promising source of natural gas. Depressurization method is considered the most effective procedure for CH4 -hydrate production. CH4 -hydrate dissociation into CH4 gas and water takes heat energy from the neighboring strata. CO2 injection into marine sediments is thought to be a potential method to enhance CH4 -hydrate recovery, because heat energy is generated by CO2 -hydrate formation. It is essential to consider the geomechanical characteristics of CO2 -hydrate-bearing sediments to ensure sustainable CH4 -hydrate production using CO2 injection. However, the mechanical properties of CO2 -hydrate-bearing marine sediments have not been clarified, although they are essentially required to simulate the geomechanical response to CO2 injection. It has recently been revealed that gas-hydrate-bearing sediments have rocklike mechanical properties due to the cementation effect of the hydrate between soil particles. In this study, the experimental methods of drained triaxial compression test for artificial CO2 -hydrate-bearing sandy sediment were developed. The mechanical properties of CO2 -hydrate-bearing specimen were compared to those of CH4 -hydrate-bearing specimen.

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