Accelerating gas production of the depressurization-induced natural gas hydrate by electrical heating

Abstract

Natural gas hydrate (NGH) will be one of the major future energy sources due to its properties of clean energy and large reserves. Depressurization is proposed as an effective method to extract natural gas from hydrate, however, the gas production from hydrate dissociation may be interrupted by ice generation and hydrate re-formation due to insufficient heat supply in the single depressurization process. To solve this issue, this work conducted simulation on accelerating gas production from the depressurization-induced methane hydrate by electrical heating. The continuous heating and intermittent heating modes were employed and then the electrical heating scheme was optimized for the comprehensive effect of high energy efficiency and high gas production rate. The results show that electrical heating is conducive to gas production from hydrate dissociation at a rapid rate. In the continuous heating, a high initial hydration saturation, low initial water saturation, low specific heat capacity, and high thermal conductivity result in the high gas generation rate and efficient electrical energy utilization (a large energy efficiency ratio). The intermittent heating has a higher efficient utilization of electrical energy than continuous heating. The optimal scheme is determined as the first-half heating type with the optimized electrical heating power of 25.6 W and the heating time of 12.5 min by the gradient descent method of AdaGrad. Compared to the baseline continuous heating case, the energy efficiency ratio (10.70) of the optimal scheme is enhanced by 24.7% with the average gas production rate (2.55 SmL/s) enhanced by 18.2%. It's hoped that the findings of this work can provide some insights into extracting natural gas from gas hydrate deposits. Electrical heating is employed to provide heat for the endothermic dissociation of methane hydrate induced by depressurization for accelerating natural gas production in this work. The electrical heating scheme is optimized to achieve high-efficient utilization of electrical energy for the fast extraction of natural gas from hydrate dissociation. • Electrical heating accelerates the depressurization induced dissociation of hydrate. • The effects of phase components and porous media properties are analyzed. • Intermittent heating has higher efficiency of energy utilization than continuous heating. • The electrical heating power is optimized by the gradient descent method of AdaGrad. • The optimal scheme is first-half heating with the optimized electrical heating power.