摘要：Geologic carbon sequestration (GCS) has been pursued as a feasible strategy to store the large amount of CO 2 to curb its emission to the atmosphere in an effort to mitigate the greenhouse effects. CO 2 hydrate, which can form when the pressure and temperature satisfy its stability condition, can provide a self-trapping mechanism for an offshore CO 2 geologic storage. For example, direct sequestration of CO 2 in the form of hydrate crystals can be achieved in the storage aquifer under the seafloor. Besides, the formation of CO 2 hydrates in an upper layer of the CO 2 storage zone can potentially provide a secondary caprock. These applications, however, require a thorough understanding of the formation and dissociation of CO 2 hydrates in porous media, which are largely unknown yet. In this manuscript, a laboratory study on the formation and dissociation of CO 2 hydrates in two different environments, a two- (CO 2 -water) or three-phase (CO 2 -water in glass beads) condition, is presented. Based on the experimental results, it can be anticipated that the pressure and temperature change will be negligible when the formation of CO 2 hydrate is induced for GCS in the actual soil/rock layers. Besides, the formation of CO 2 hydrate in porous media may be faster, compared to the two-phase bulk condition that has been typically used in many laboratory studies, as solid grains help accelerate the hydrate formation by providing nucleus sites of crystals. Further elaborations on the role of solid grains would bring a clear path for the feasible application in the subsea area.
