Feasibility assessment of enhancing permeability and stability in marine hydrate reservoirs with dual-enhanced stimulation: Slurry-sediment cementation characteristics

Natural gas hydrate reservoirs in the South China Sea exhibit weak cementation, low strength, and low permeability, which severely restricts their commercial viability. To overcome these challenges, we propose an innovative dual-enhanced stimulation method involving slurry injection via splitting grouting. This slurry undergoes in-situ solidification, forming porous, high-strength, and high-permeability channels. The method's success hinges on understanding cementation patterns between the slurry and reservoir sediments, along with the permeability dynamics at the cementation interface. This study explored the microscopic features of the slurry-sediment cementation interface and evaluated changes in permeability nearby and within the slurry-sediment composite. It was observed that during the solidification process, the slurry invaded the sediments, resulting in an interface thickness more than 55µm. This invasion altered the pore structure of the sediment at the interface, reducing its porosity by more than 40 %, which in turn decreased gas permeability and damaged the permeability of the slurry-sediment coupled sample. After consolidation, the permeability damage of the coupled sample reached about 75 %, but it decreased to 27 % with the discharge of the permeability-enhancer in the slurry. Additionally, the evaluation of the pressure drop coefficient revealed that hydrate reservoirs stimulated with polyurethane slurry exhibit superior permeability compared to those transformed with guar gum fracturing fluid and pure water. This suggests that the dual-enhanced stimulation slurry causes minimal damage to reservoir permeability, demonstrating its feasibility in enhancing both permeability and strength of the reservoir. This study presents a novel stimulation method for the safe and efficient extraction of marine hydrates. (a) In situ solidification of slurry after fracturing; (b) Local map of slurry vein; (c) Variation of coupled sample permeability damage with the permeability-enhancer discharged.