Impact of Varied Depressurization Rates on Gas Production and Heat Supply in Hydrate Dissociation

Natural gas hydrate is widely recognized as a promising energy source, with depressurization emerging as the preferred method due to its simplicity and cost-effectiveness. Employing an appropriate depressurization strategy is paramount for maximizing gas production efficiency, especially when faced with constraints in the reservoir heat supply. However, the precise influence of the depressurization rate on the gas production rate and heat supply remains unclear. In this study, we employ a fully coupled thermo-hydro-chemical (THC) model to simulate 60 days of hydrate dissociation using a horizontal well under various depressurization schemes: decelerating depressurization (DD), regular depressurization (RD), and accelerated depressurization (AD). We investigate the effects of dynamic changes in the depressurization rate on gas production, multiphysics response and reservoir heat supply. Our findings indicate that the influence of the depressurization rate on the multiphysics response is most pronounced during the initial depressurization stage. A positive correlation between the gas production rate and the depressurization rate is observed. The amplitude of the gas production rate fluctuations is more significant at higher depressurization rates, and these fluctuations intensify as the depressurization rate increases. From a heat supply perspective, the sensible heat supply ratio increases with the depressurization rate. Gas production is primarily driven by flow dynamics and propelled by sensible heat during depressurization and the early stages of constant pressure. Subsequently, it is controlled by the heat supply and driven by the ambient heat transfer. Therefore, additional heat replenishment can enhance gas production and improve economic viability when sensible heat supply is not predominant. Such findings hold crucial reference value for the commercial exploitation of hydrate resources.