Anomalous preservation of pure methane hydrate at 1 atm

Direct measurement of decomposition rates of pure, polycrystalline methane hydrate reveals a thermal regime where methane hydrate metastably "preserve s" in bulk by as much as 75 K above its nominal equilibrium temperature (19 3 K at 1 atm). Rapid release of the sample pore pressure at isothermal cond itions between 242 and 271 K preserves up to 93% of the hydrate for at leas t 24 h, reflecting the greatly suppressed rates of dissociation that charac terize this regime. Subsequent warming through the H2O ice point then induc es rapid and complete dissociation, allowing controlled recovery of the tot al expected gas yield. This behavior is in marked contrast to that exhibite d by methane hydrate at both colder (193-240 K) and warmer (272-290 K) test conditions, where dissociation rates increase monotonically with increasin g temperature. Anomalous preservation has potential application for success ful retrieval of natural gas hydrate or hydrate-bearing sediments from remo te settings, as well as for temporary low-pressure transport and storage of natural gas.