Fracture Initiation and Slurry Diffusion in Marine Hydrate Reservoirs during Dual-Enhanced Stimulation

Abstract

Dual-enhanced stimulation is an innovative technology aimed at enhancing the permeability and strength of marine hydrate reservoirs by injecting and solidifying a dual-enhanced slurry, forming high-permeability slurry veins for gas and water flow, which is essential for commercial hydrate extraction. This study investigates the mechanisms behind fracture initiation and slurry diffusion in marine hydrate reservoirs during the dual-enhanced stimulation process with the goal of improving stimulation effectiveness. The results show that slurry veins diffused rapidly in the early stage, eventually forming a shuttle shape with a thicker middle section and thinner sides. As hydrate saturation increased, sediment particle cementation strengthened, reducing the slurry filtration. This required higher pressure for fracture initiation but also extended the diffusion distance and the area of the slurry veins. Increasing the injection angle created a complex, uneven stress field near the wellbore, making fracture initiation more challenging. The maximum diffusion distance was achieved at a 30° injection angle, although the slurry vein shape became irregular. Higher injection rates improved slurry diffusion, and at 500 L/min, the diffusion radius reached 10 m and covered nearly 240 m², demonstrating significant improvement in the stimulation effect. The sensitivity analysis indicates that the injection angle had the greatest influence on the initiation pressure, while changes in hydrate saturation had minimal impact. Injection rate was the key influencing factor to the diffusion radius; however, it is essential to determine the optimal point to achieve the appropriate diffusion radius. These findings offer practical insights for applying dual-enhanced stimulation technology in marine hydrate reservoirs and will guide future engineering efforts.