Natural gas hydrate that exists in the ocean sediment is thought to constitute a large methane gas reservoir and is expected to be an energy resource in the future. In order to make recovery of natural gas from hydrates commercially viable, hydrates must be dissociated in-situ. Meanwhile, steam injection method is practically used for oil sand to recover heavy oil and recognized as a means that is commercially successful. In this study, the steam injection method for methane hydrate bearing sediments has been examined and discussed on an experimental basis. New experimental apparatus for steam injection has been designed and constructed. In-situ methane hydrate bearing sediments were simulated in laboratory scale. And just after the depressurization, inner temperature at each area dropped down to approximately 0 deg C caused by the combination of endothermic reaction of hydrate dissociation and exothermic reaction of ice formation. Also, the phase transition from vapor water to liquid water in methane hydrate bearing sediments was observed. Obtained temperature profile suggested that phase transition from steam to liquid water occur at upstream area (from 25mm to 75mm from top of the core). Additionally, reaching point of steam moved back and forth around this area. From the gas production behavior, it can be concluded that roughly 44 % of total hydrate origin gas was produced after steam injection.
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).