Numerical Simulation on Geothermal Energy-Assisted Depressurization for Gas Hydrate Extraction

Natural gas hydrates are characterized by abundant reserves, wide distribution, and high energy density, while geothermal energy also holds significant development potential. Conventional hydrate dissociation methods face challenges in the later stages of production, such as insufficient driving force for dissociation and secondary hydrate formation. This study explores the approach of utilizing deep-sea geothermal energy to assist in the extraction of hydrate. The aim is to achieve efficient exploitation of hydrate while expanding the applications of geothermal energy. A field-scale coupled thermo–hydro–mechanical–chemical (THMC) injection-production numerical model is established, taking a typical hydrate reservoir in the South China Sea as the study area. The engineering feasibility of geothermal-assisted hydrate extraction is evaluated through numerical simulations. Injection temperature, extraction rate, and well layout are systematically analyzed to optimize production performance, with particular focus on the evolution of physical fields, hydrate dissociation, and geothermal formation temperature stability. The novelty of this study lies in the proposal of a closed-loop ‘in-situ geothermal extraction and reinjection’ system, and the systematic optimization of its coupled THMC responses, which has received limited quantitative investigation. The results indicate that an injection temperature of 50 °C and an injection rate of 500 m³/d provide the most favorable production performance under the investigated conditions. Compared with conventional depressurization, the optimized geothermal-assisted scheme increases cumulative gas production by approximately 40% after 600 days. Horizontal well configurations outperform vertical wells, whereas excessively close well spacing reduces thermal stimulation efficiency because of hydraulic interference. Temperature variations in the geothermal layer during the simulated extraction period are minimal, indicating favorable operational stability under the investigated conditions. In summary, geothermal-assisted depressurization enhances hydrate extraction efficiency and expands geothermal applications, offering a promising approach for future development.