Formation / dissociation behavior of clathrate hydrate in bentonite or kaolin suspension with or without sodium chloride was experimentally investigated for safe gas production from the natural gas hydrate reservoir. Raman spectroscopic analysis is conducted to investigate the property of formed hydrate from bentonite or kaolin suspension. Vapor pressures of water of these suspensions, which are related to hydrate equilibrium conditions, are also determined. The crystal structures of clathrate hydrates formed from clay suspensions can be determined as sI. However, the small cavity occupancies of hydrate formed from calcium bentonite and kaolin are 0.792 and 0.794 respectively, which are approximately 10 % smaller than that of pure MH or hydrate formed from sodium bentonite. Obtained vapor pressure suggests that equilibrium T-P condition in clay suspension without NaCl does not shift within the concentration region of 1 to 10 wt%. However, for NaCl 20 wt% - sodium bentonite 10 wt% suspension and NaCl 20 wt% - calcium bentonite 10 wt% suspension, the vapor pressures are rather smaller than that of NaCl 20 wt% solution. It suggests the equilibrium pressures in these suspensions become high compared to that in NaCl 20 wt% solution.
Natural gas hydrates are crystalline compounds that can contain a large amount of natural gas (Sloan and Koh, 2008). Owing to recent seismic exploration and geological research, it is widely known that natural gas hydrate that exists in the sediment constitutes a large natural gas resource and is expected to be an energy source in the future (Makogon, 1981; Brooks et al., 1986; Kvenvolden, 1988; Kvenvolden et al., 1993; Okuda, 1993; Gornitz and Fung, 1994; Sassen, 2001; Fujii, 2008). Natural gas hydrate will be dissociated mainly by the depressurization in the geological formation for commercial gas recovery. Fig. 1 shows an example of gas production scheme.
