Effects of CH4-CO2 replacement in hydrate-bearing sediments on S-wave velocity and electrical resistivity

CH4-CO2 replacement has been considered as a method for methane production from hydrate-bearing sediments to maintain sediment stability. Sediment stability has been studied at both the particle scale and mesoscale. However, the shear stiffness of sediments has not yet been explored. Moreover, the effects of CO2 and CO2-N-2 mixtures as injection fluids on sediment stability remain unclear. Thus, this study aimed to determine the variations in shear wave velocity and electrical resistivity during hydrate formation, CH4-CO2 replacement, and hydrate dissociation using two types of injecting fluids (CO2 and CO2-N-2 mixture). The results demonstrated that hydrate-bearing sediment could maintain its stability during CH4-CO2 replacement by injecting CO2 or CO2-N-2 mixture. Furthermore, injecting CO2-N-2 mixture was more efficient for methane production than injecting CO2. The Results also revealed that injecting CO2-N-2 mixture could lead to higher stability of sediments during CH4-CO2 replacement than injecting CO2, although the difference in sediment stability was small between the two cases.