Fluid flow mechanisms and heat transfer characteristics of gas recovery from gas-saturated and water-saturated hydrate reservoirs

Due to the huge reserves, natural gas hydrate is considered as a potential energy resource in future. Therefore, developing methods of gas recovery from hydrate reservoirs for commercial production are attracting extensive attention. In this work, hydrate dissociation and gas recovery from the gas saturated and water-saturated hydrate accumulations are investigated in a pilot-scale hydrate simulator. Depressurization, thermal stimulation, and depressurization assisted thermal stimulation method are adopted in this work. Furthermore, the mechanisms of fluid flow and the heat transfer during hydrate dissociation in different hydrate accumulations are elucidated by large-scale experimental results. The experimental results indicate that the fluid flow mechanisms and the heat transfer characteristics during the gas recovery from hydrate reservoirs are greatly influenced by the initial water saturation. The Optimum gas production method is also different for different hydrate accumulations. The depressurization is optimized method for hydrate dissociation in the gas-saturated reservoir considered from the aspect of gas-water ratio. Thermal stimulation results in the lowest gas-water ratio and the lowest hydrate dissociation ratio, and is not effective for both the gas-saturated and water-saturated hydrate reservoir. The depressurization assisted thermal stimulation is the optimum method for the hydrate dissociation in the water-saturated sample. (C) 2017 Elsevier Ltd. All rights reserved