New gas-hydrate phase; synthesis and stability of clay-methane hydrate intercalate

Intercalated Na-rich montmorillonite-methane hydrate was synthesized for the first time. The upper limit of stability for the intercalate in pressure and temperature is parallel to that of methane hydrate but at temperatures that are approximately 0.5-1 degrees C lower than for methane hydrate. The low-temperature stability of the intercalate is at -11.5+ or -3 degrees C at approximately 40 bar, where methane and some H (sub 2) O are expelled from the region between the silicate layers (interlayer). In contrast, methane hydrates do not dissociate at these low temperatures. We conclude that at conditions similar to where methane hydrate is stable, smectite may intercalate with methane hydrate and provide additional sinks for methane. The limitation in the stability of smectite-methane hydrate intercalate at low temperatures suggests that, if present in large quantities, it may release at decreasing temperatures sufficient methane to ameliorate a planetary cooling event.