Investigation of Fracture Orientation Effects on Caprock Sealing for Enhanced Gas Hydrate Recovery

Caprock sealing has been proposed to improve gas hydrate production by redirecting pressure propagation and strengthening near-wellbore pressure drawdown. Integrating it with hydraulic fracturing offers further productivity gains. However, the influence of fracture orientation on caprock sealing efficacy and associated geomechanical responses remains insufficiently understood. This study applies a coupled thermo-hydro-mechanical-chemical (THMC) numerical model to evaluate the combined effects of fracture orientation and localized caprock sealing strategies in a low-permeability marine hydrate reservoir analogous to the Shenhu Area, South China Sea. Results show that caprock sealing modestly increases gas production while markedly reducing subsidence, with performance driven by fracture-sealing interactions. Vertical fractures accelerate pressure depletion and gas recovery but worsen compaction and subsidence, whereas horizontal fractures produce milder responses. Underburden sealing is more effective in the early stage due to faster downward propagation of the dissociation front, whereas combined overburden-underburden sealing provides more comprehensive long-term benefits. However, sealing impedes convective heat supply, limiting late-stage productivity. In the modeled conditions, caprock sealing increases the gas recovery ratio by approximately 7%, improves the gas-to-water ratio by 31%, and reduces wellhead subsidence by up to 37%. The results provide engineering guidance for selecting fracture-sealing strategies to balance gas recovery, gas-to-water ratio, and subsidence control in marine hydrate production.