Optimization of well placement for CO2 sequestration in subsea hydrate reservoirs considering field synergy and inter-well interference

Carbon dioxide geological sequestration is a critical pathway for achieving carbon neutrality. Previous studies on hydrate-based CO2 sequestration have primarily focused on phase equilibrium, formation kinetics, and reservoir-scale capacity assessments. However, well placement optimization—extensively investigated for hydrate production—remains underexplored for CO2 sequestration in subsea hydrate reservoirs, particularly regarding systematic comparisons of different configurations and their effects on multi-physical field synergy, inter-well interference, and coupled deformation responses. Using multi-field coupled numerical simulations, this study systematically investigates the effects of various well placement systems on CO2 sequestration behavior, focusing on multi-physical field evolution and inter-well interference control. Results show that the three-point well pattern achieves a cumulative sequestration of 9.23 × 107 kg, 2.14 times that of a single well, highlighting its potential for large-scale carbon storage. Horizontal well spacing exhibits a non-monotonic relationship with performance, identifying an optimal spacing window. Vertical layer and spatial configuration further enhance efficiency. Multi-field analysis reveals that a hydrate cap layer forms gradually, with CO2 and hydrate exhibiting highly overlapping distributions where field synergy concentrates, while pressure and temperature fields remain stable—key indicators for storage safety. The Field Synergy Enhancement Factor (FGE) declines exponentially from 3.00 to 2.16, quantifying inter-well interference dynamics. Reservoir deformation displays creep-like growth, with shallow uplift (max 0.6 m) causally linked to a central deformation core zone. Rational design of well spacing, vertical layers, and spatial configuration is critical for balancing capacity and stability. This study provides a theoretical basis for efficient well placement in marine hydrate reservoir CO2 sequestration.