Gas hydrate exploitation and carbon dioxide sequestration under maintaining the stiffness of hydrate-bearing sediments

To improve the stratum mechanical properties and prevent the geological disaster, we present a new approach by executing CH4 hydrate exploitation and CO2 sequestration below the freezing point of water to maintain the stratum stiffness during and after hydrate exploitation. An experimental method to clearly show the evolution of the stratum mechanical properties was built and a series of experiments were conducted to simulate the CH4 exploitation and CO2 sequestration process below and above the freezing point of water. The stratum stiffness was found to be maintained during the whole hydrate exploitation process when below the freezing point. Moreover, the presence of ice improves the stratum stiffness due to cementing the sandy grain. The CO2 injection into the hydrate-bearing sediments would further enhance the mechanical properties and realize a CO2 geological sequestration. Compared with hydrate exploitation above the freezing point, the CH4 recovery efficiency is a little lower when under below the freezing point and it decreased with the increased hydrate saturation due to the CH4 hydrate being surrounded by the generation of ice from hydrate dissociation. This phenomenon could be modified by injecting CO2, from which the CH4 recovery efficiency obviously improved for hydrate exploitation below the freezing point.