Impact of fracture orientation on gas hydrate extraction using horizontal well depressurization and hydraulic fracturing

Natural gas hydrates are considered a potential future energy resource due to their vast reserves. However, commercial extraction remains highly challenging, particularly in low-permeability hydrate reservoirs. Hydraulic fracturing, applied successfully in shale gas reservoirs, has been proposed to promote natural gas hydrates recovery. Previous models often oversimplify the complex geological characteristics of hydrate reservoirs and provide limited consideration of the impact of fracture orientation. In this work, a coupled THMC model was developed based on the geologic data of the multilayered gas hydrate bearing sediments in the South China Sea to investigate the effect of fracture orientation on gas production performance and geomechanical responses. The key findings are as follows: (1) reducing fracture height is beneficial for improving recovery efficiency and minimizing geological risks, though excessively small fractures may hinder production; (2) fracture orientation primarily influences the distribution of stress concentration but not its intensity; (3) optimizing fracture orientation and reducing caprock permeability can enhance extraction efficiency, yet production still falls short of commercial targets; (4) fracture orientation affects subsidence by altering the direction of pressure drop and the degradation of reservoir mechanical properties. These findings offer new insights into fracture design for safe and efficient hydrate extraction.