Experimental measurements of mechanical properties of carbon dioxide hydrate-bearing sediments

•Decreasing temperature and porosity will enhance the strength of CO2 hydrate sediment.•Increasing strain rate will enhance the strength of CO2 hydrate sediment.•The strength of CO2 hydrate sediment is also sensitive to confining pressure.•The strength of CO2 hydrate sediment is larger than that of CH4 hydrate sediment.•CH4–CO2 replacement method can remain the stability of gas hydrate sediment.

The CH4–CO2 replacement method to recover methane from hydrate-bearing sediments has received great attention because it enables the long term storage of CO2 and is expected to maintain the stability of gas hydrate-bearing sediments. In this paper, the mechanical properties of CO2 hydrate-bearing sediments were measured by a low-temperature and high-pressure triaxial compression apparatus. The strength differences between the CO2 and CH4 hydrate-bearing sediments were then analyzed to evaluate the safety of the CH4–CO2 replacement method. The strength of the CO2 hydrate-bearing sediments was found to increase as the temperature and porosity decreased and as the strain rate increased. When the confining pressure was less than 5 MPa, the strength of the CO2 hydrate-bearing sediments also increased as the confining pressure increased. However, owing to pore-ice melting and particle breakage, the strength of the CO2 hydrate-bearing sediments decreased as the confining pressure increased for confining pressures exceeding 5 MPa. The strength of the CO2 hydrate-bearing sediments was found to be larger than that of the CH4 hydrate-bearing sediments, with the strengths of the CH4 and CO2 hydrate-bearing sediments varying with the influence factors in a nearly identical fashion. The results indicate that the stability of gas hydrate-bearing sediments could be maintained using the CH4–CO2 replacement method to recover methane from these sediments.