Effect of Hydrate Saturation on the Methane Hydrate Dissociation by Depressurization in Sediments in a Cubic Hydrate Simulator

This study presents the three-dimensional (3D) cubic hydrate simulator (CHS) to analyze the methane dissociation phenomena from hydrate-bearing sediment with different hydrate saturation. The experiments by depressurization have been carried out at the environmental temperature of 281.15 K, the dissociation pressure of 5.0 MPa, and in the hydrate saturation range of 17.0–43.2%. The hydrate dissociation process consists of two periods: the depressurizing period and the steady-pressure period. In the depressurizing period, the hydrate dissociation occurs in the whole reactor. The cumulative gas production is similar, and the gas production rate is affected by the depressurization rate and the water production in this period. The cumulative water production increases with the decrease of the hydrate saturation in the whole depressurization process. In the steady-pressure period, the cumulative gas production increases with the increase of the hydrate saturation. The average gas production rate first increases with the increase of the hydrate saturation and then decreases at hydrate saturation of 43.2%. The water production during the steady-pressure period only occurs in the experiments with the high hydrate saturation. The temperatures in different regions in the reactor change with similar degrees in the depressurizing period and have the similar lowest values for different experiments. In the steady-pressure period, the temperatures increase gradually from the inner-wall region to the center region. On the basis of the calculation of the energy balance, it was found that the ratio of the sensible heat of the reservoir to the latent heat of the hydrate dissociation decreases with the increases of the hydrate saturation and the dissociation pressure.