In this study, unloading-reloading tests were conducted for artificial methane hydrate sediment samples under triaxial compression and the mechanical behaviors were discussed. In the early stage of axial loading, where consolidation of the sample would occur, the slope of unloading-reloading curve increased; in the following stage, where dilatancy behavior would be a dominant deformation mechanism, the slope decreased slightly. The findings may be of some help not only to understand the deformation mechanism but also to construct a mechanical model or a constitutive equation for methane hydrate sediment.
Methane hydrate is anticipated to be a promising energy resource of natural gas, since a large amount of reservoir exists in marine sediments or in permafrost regions worldwide (Kvenvolden, 1988; Kvenvolden et al., 1993; Okuda, 1993). It is important to predict mechanical behaviors of methane hydrate reservoir for sustainable production of methane hydrate. Deformation mechanism of methane hydrate sediment has a great significance not only on mechanical stability of methane hydrate reservoir in production but also on evaluation of gas productivity from methane hydrate reservoir. Although some previous studies have reported about mechanical properties of artificial methane hydrate sediment sample in triaxial compression test (Masui et al., 2005; Winters et al., 2005; Masui et al., 2008; Miyazaki et al., 2008), almost no information is available concerning the property in unloading and reloading process. Mechanical properties in unloading and reloading process during a triaxial compression test may be of some help to understand the deformation mechanism or construct a mechanical model for methane hydrate sediment. In this study, unloading-reloading tests were conducted for artificial methane hydrate sediment samples under triaxial compression and the mechanical behaviors were discussed.
In this study, the method of triaxial compression test followed previous studies (for example, Masui et al., 2005).