The replacement of CH4 by CO2 in gas hydrate bearing sediments has received great attention since it may enable long-term storage of CO2 which could mitigate the "Global Warming Effects", and facilitate CH4 recovery as a potential future energy resource. Elasticity and Stability of CH4 and CO2 hydrate are crucial for development of CH4 hydrate and CO2 storage in the field.
In this study, molecular dynamics simulations were performed to determine the elastic moduli of CH4 and CO2 hydrate for at one hundred pressure-temperature data points, respectively. The conditions represent marine sediments and permafrost where gas hydrate occurs. The Young's modulus and shear modulus of the CO2 hydrate increase anomalously with increasing temperature, whereas those of the CH4 hydrate decrease regularly with increase in temperature. We ascribe this anomaly to the kinetic behavior of the linear CO2 molecule, especially those in the small cages. The cavity space of the cage limits free rotational motion of the CO2 molecule at low temperature. With increasing in temperature, the CO2 molecule can rotate easily, and enhance the stability and rigidity of the CO2 hydrate. This work provides a key database for the elastic properties of gas hydrates, and molecular insights into stability changes of CO2 hydrate from high temperature of ~5 °C to low decomposition temperature of ~-150°C. Besides, the obtained results are significant with regard to CO2 storage in the form of CO2 hydrate in the field.