It is noted that natural gas hydrate exists in geological formations and constitutes a potentially large natural gas resource for the future. To make recovery of natural gas from hydrates commercially viable, hydrates must be dissociated in-situ. At the present stage, depressurization method is expected to be a main dissociation procedure because of its high energy profit ratio and so on. Whereas, there is a worry that some interruptions for gas production i.e. plugging by hydrate formation will occur. Also there is a demand to enhance the recovery ratio of natural gas. In this study, inhibitor injection method or steam injection method combined with depressurization have been examined using laboratory made methane hydrate bearing sediment. As a result, it becomes clear that the combined method contributed the fastest gas production rate compared to the other methods. The advantages of combined method become remarkable as higher pressure condition (smaller depressurization from initial pressure). The production rate of combined method become faster as the pressure is lower.
Natural gas hydrates are crystalline compounds that can contain a large amount of natural gas (Sloan, 1998). 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). To make recovery of natural gas from hydrates commercially viable, hydrates must be dissociated in-situ. At the present stage, depressurization method is expected to be a main dissociation procedure because of its high energy profit ratio and so on. Whereas, there is a worry that some interruptions for gas production i.e. plugging by hydrate formation will occur.
