Enhancing Multi-gas Recovery and CO ₂ Sequestration in Deepwater Clayey-Silt Reservoirs via a Novel Reservoir-Overburden Stimulation Strategy

Efficient and safe exploitation of deepwater multilayer gas systems, where shallow gas, natural gas hydrate, and conventional gas coexist in clayey-silt reservoirs, remains constrained by the competing requirements of permeability enhancement and geohazard control. Here, we propose a Reservoir-Overburden Stimulation (ROS) strategy based on directional splitting grouting to couple multi-gas recovery with in-situ CO 2 sequestration. A field-scale numerical model, geologically initialized using Shenhu logging data and validated for hydrate depressurization and multiphase-flow behavior, was established to quantify the coupled “Flow-Sealing” response. Sensitivity analyses show that slurry-vein width is the dominant parameter controlling reservoir stimulation: increasing the vein width to 0.10 m enhanced short-term gas production by 11.97% by reducing flow resistance. By contrast, excessive fracture extension (>75 m) induced a water-breakthrough effect, hydraulically connecting water-bearing zones and reducing production by 0.78% relative to the baseline. For risk control, top-layer overburden grouting provided the most effective hydraulic barrier and maintained a high gas-to-water ratio, although standalone sealing contributed negligible gas enhancement (<0.1%). Integrating these optimized reservoir and overburden treatments, the ROS strategy establishes a high-conductivity reservoir network while forming a low-permeability, CO 2 -mineralized overburden barrier. The resulting carbonate-bearing consolidation is expected to improve sealing integrity, support long-term carbon retention, and mitigate reservoir-compaction risks. This work provides a mechanistic and quantitative framework for coupling gas recovery, water-intrusion control, and carbon sequestration in deepwater clayey-silt reservoirs.