Solubility or CO2 in hydrate region we measured. The data show the solubility decreases of the temperature. This temperature dependence, which seems to be contradictory to the common knowledge for solubility of a gas, was well estimated only from published data of the CO2 solubility In non-hydrate region and phase equilibrium diagrams or CO2 waters and methane-waters systems. This conclusion results in reconsideration of assessments for various CO2 sequestration methods in the ocean where the solubility extrapolated from non-hydrate region has been used.
As a promising measure to mitigate the global warming, Albanese and Steinberg (1980) proposed to sequestrate CO2 collected from power plants and other sources into the vast oceans. The CO2 sequestration in the ocean can mainly be classified into the following two methods: the dissolution method in which liquid CO2 is released in depths shallower than 2000 meters and dissolved CO2 diffuses, and the storage method in which liquid CO2, is pooled in hollows on ocean basins deeper than 3500 meters where liquid CO2 is heavier than saturated CO2 rich sea water. Figures 1and 2 show concepts of the above two methods proposed by the authors (Aya and Yamane,1996), respectively. These CO2 sequestration methods have some advantages and shortcomings. In the dissolution method, a high CO2 concentration region should appear although the increase of CO2 concentration is negligible after a completion of the diffusion. On the other hand, in case of the storage method, undesirable effects to the environment in the vicinity of a storage site is concerned although the influenced area can be limited. The authors, from this point of view, have conducted some experimental studies on stability and mechanical properties of the CO2 hydrate, using a high pressure facility which can simulate pressure and temperature conditions at 3000 meters depth in the ocean.
