Mechanism Analysis of Multi-Cluster Fracture Interference in Horizontal Wells of Hydrate Reservoirs in the South China Sea

At present, reservoir reconstruction technology is a possible and practical way to solve the commercial exploitation problem of hydrates, such as low production, limited production range, and high production cost. The research mechanism of hydraulic fracturing in NGH (natural gas hydrate) reservoirs has not formed a theoretical system for the most common reservoir reconstruction technology. In this work, according to the measured geological conditions of site GMGS3-W19, a multi-cluster hydraulic fracturing model for horizontal wells in NGH reservoirs is established with the extended finite element method. The effects of fracture spacing, hydrate saturation, and horizontal in situ geostress difference on the final propagation path of multi-cluster fractures are analyzed. When the alternating fracturing and sequential fracturing are adopted, the subsequent fracture will have a certain extrusion force on the formed fractures, which makes the existing fractures continue to propagate and produce a second expansion. The total lengths of fractures generated by alternating and sequential fracturing modes for values of fracture spacing from 8 to 20 m are longer than that of simultaneous fracturing mode. The hydrate saturation increases from 20 to 60%, and the fracture propagation path hardly changes. However, the fracture propagation of HBS (hydrate-bearing-sediments) with high hydrate saturation is hindered, which leads to a small fracture length in alternating fracturing and simultaneous fracturing modes. When sequential fracturing is adopted, the interference between fractures of HBS with low hydrate saturation is apparent, and the bending degrees of hydraulic fractures are large. When the hydrate saturation reaches 60%, the last fracture will hardly bend and expand along the perforation direction. The difference of horizontal geo-stress increases, and the interference between fractures is more substantial, specifically reflected in the increase of the second fracture expansion lengths and further expansion along the direction of the maximum horizontal geo-stress.