The determining factor of hydrate dissociation rate in the sediments with different water saturations.

In nature, gas hydrate is mainly distributed in permafrost region and deep ocean sediments. For these two types of hydrate reservoirs, water contents in the sediments were different. The water content has a large influence on the characteristics of heat transfer and fluid flow in the sediments, thereby affecting the hydrate dissociation behavior. In this paper, the experiments of hydrate dissociation by depressurization in sediments with different water saturations were conducted. The influences of water saturation on the pressure, the temperature, the gas production, the water production, and the hydrate dissociation rate were analyzed. The experimental results showed that, in the depressurization stage (DS), the rate of pressure dropping and the amount of hydrate reformation increased with the raise of the water saturation in the sediments. In the constant pressure stage (CPS), although the heat conduction rate of the sediments increased with the increase of the water saturation, the mass transport rate of the gas released from hydrate dissociation was limited due to the increase of water saturation. As a result, the hydrate dissociation rate decreased with the increase of the water saturation in the sediments. According to these experimental results, during the hydrate dissociation in the sediments with different water saturations, the hydrate dissociation rate is determined by the mass transport rate of the gas released from the hydrate dissociation. For the hydrate reservoirs with the high-water saturation, the hydrate dissociation rate is largely limited by the diffusion rate of gas released from hydrate dissociation. Hence, the key factor to improve the hydrate dissociation rate in the sediments with high water saturation is to increase the diffusion rate of gas in the sediments. • Hydrate dissociation rate decreased with the increase of water saturation in the sediments. • Water surrounding the hydrate particle limited the diffusion of gas released from hydrate. • The mass transport rate of gas released from hydrate determined the hydrate dissociation rate. [ABSTRACT FROM AUTHOR]