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.