Investigations on performance of hydrate dissociation by depressurization near the quadruple point

Depressurization is an effective method to exploit natural gas hydrate reservoirs. However, ice might be formed due to the endothermic effect of hydrate dissociation, which will have a significant influence on gas production. In this work, a numerical model is established to investigate the hydrate dissociation performance by depressurization near the quadruple point. The impact of production pressure and intrinsic permeability on gas production and ice formation are also analyzed. It is revealed that the ice tends to be formed around the perforated interval due to the lower production pressure. A decrease in the effective porosity and permeability due to ice formation has been observed. But in fact, the formed ice has played a positive role in enhancing gas production owing to the released latent heat during ice formation. A large amount of ice is formed which results in a higher gas production rate when the production pressure is lower. The gas production rate and ice formation are greatly enhanced in the early production stage of a hydrate reservoir with a relatively high intrinsic permeability. For a hydrate reservoir with low permeability, ice formation is beneficial for gas production in the long term.