Indexed by:Journal Papers

Date of Publication:2020-06-01

Journal:MARINE AND PETROLEUM GEOLOGY

Included Journals:EI、SCIE

Volume:116

ISSN No.:0264-8172

Key Words:Hydrate dissociation; Magnetic resonance imaging; MR/MRI-Compatible metallic core holder; Phase evolution; Capillary-trapped residual gas; Elevated pore pressure

Abstract:Methane hydrate deposits worldwide are vast potential sources of natural gas. Although field tests, and many laboratory studies, of hydrate dissociation have been performed, long term gas recovery from hydrate deposits still requires a comprehensive knowledge of the pore gas pressure and related phenomena. Pore gas pressure can significantly affect the safety and efficiency of gas production from hydrate deposits. Capillary-trapped residual gas saturation, known to cause elevated pore gas pressure during methane hydrate dissociation, was measured by magnetic resonance. Elevated pore gas pressure was estimated to be 8500 psi. Different molecular species and fluid environments produced during the methane hydrate dissociation process were discriminated. The results show that the majority of gas is initially confined as capillary-trapped gas upon dissociation. The evolution of water and gas saturations was measured as a function of time. Water migration, bed failure, and crack growth, related to elevated pore gas pressure, were observed both spatially and temporally resolved. Hydrate dissociation proceeded from the sand pack exterior to the interior, in a shrinking core manner, due to heat transfer effects. It was observed that hydrate dissociation resulted in pronounced water migration toward the low-pressure surface.
   This study was undertaken with advanced magnetic resonance imaging (MRI) and magnetic resonance (MR) methods employing a MR/MRI-compatible metallic core holder. A hydrate-bearing sand pack, with 96% initial hydrate saturation, underwent dissociation by depressurization at 290 psi and 4 degrees C.