Dissociation characteristics of methane hydrates in South China Sea sediments by depressurization

Abstract

Marine methane hydrate is a considerable energy source for use in the near future. With great obstacles to spot production, researchers are focusing on the production characteristics of hydrates in various experimental systems, such as glass beads, clay, silica sand and so on. This study investigated the production behaviors of methane hydrate in the real South China Sea sediments using depressurization method. The hydrate saturations of the remolded hydrate-bearing sediments ranged from 10.10% to 23.76%. The results indicate that an 8% increase of hydrate saturation can prolong the dissociation duration under the same backpressure of 2 MPa by 120 min. In addition, the excess temperature drop caused by the depressurization may induce the unpredictable occurrence of hydrate reformation or icing; therefore, a double depressurization method that depressurizes to 2 MPa (second stage) after 20 min maintenance at 4 MPa (first stage) is employed in order to shorten the temperature drop in the first stage and increase the dissociation rate in the second stage. The results of this study are significant for the spot production of marine hydrates in order to achieve high efficient gas production.