Large scale experimental investigation of influence of heat conduction and heat convection on hydrate dissociation by depressurization in sandy sediment

Abstract

Natural gas hydrate can be regarded as alternative energy source in future due to huge reserves of methane gas trapped in hydrate bearing formations. According to the laboratory studies and field programs, depressurization method has been considered as the most cost-effective and practical way to dissociate gas hydrates. Rates of hydrate dissociation by depressurization mainly depend on heat transfer rate. The heat transfer during hydrate dissociation mainly includes heat conduction and heat convection. In this work, the Pilot-Scale Hydrate Simulator (PHS), with an inner volume of 117.8 L, was applied to investigate the influence of heat conduction and heat convection on hydrate dissociation. Different thermal boundary conditions and different flow directions during gas recovery from hydrate reservoir by depressurization were performed in the PHS. The experimental results indicate that hydrate dissociation rate with isothermal boundary is fast than that with semi-adiabatic boundary. However, the influence of heat convection direction on heat dissociation in the CP stage may not be obviously. The heat transfer rate in the CP stage of the depressurization mainly depends on the heat conduction rate.