The injection of CO2 into CH4 hydrate-bearing sediments causes the release of CH4 and the formation of CO2 hydrate within the CH4 hydrate stability field. CH4-CO2 replacement allows for the recovery of an energy source, CH4, while trapping CO2. In this study, we monitor pore-scale changes in electrical resistance and relative stiffness during CH4 hydrate formation, CH4-CO2 replacement, and hydrate dissociation; experiments are also observed using high-resolution time-lapsed photography. Results show that CH4-CO2 replacement occurs locally and gradually so that the overall hydrate mass remains solid and no stiffness loss should be expected at the sediment scale. Other experimental results confirm the slow diffusion of CH4 through the hydrate shell that forms between water and gas; this may allow for the coexistence of gas-hydrate-water phases for long periods of time.