2D discrete element simulation on the marine natural gas hydrate reservoir stimulation by splitting grouting

Reservoir stimulation offers the possibility to solve the problems of low single well production, small mining range, and short stabilized production in NGH field trials. Compared with traditional hydraulic fracturing, split grouting technology has the advantages of both enhancing the gas-water seepage capacity of the reservoir and maintaining the stability of the reservoir. In this study, a 2D discrete element method was used to establish a finescale model for NGH reservoir and numerical tests were conducted on split grouting. The pattern, direction and range of the grouting expansion were analyzed under different conditions of hydrate saturation, injection pressure, grout viscosity, injection well size, in-situ stress, and the number of injection wells. The results show that the grouting process can be roughly divided into two stages: squeeze grouting and split grouting. Squeeze grouting occurs in the early stages, and grout expansion is limited in the wellbore area. Subsequently, split grouting occurs always along the direction of the maximum principal stress when injection pressure is high enough, creating dendritic grout veins inside the reservoir and enhancing the connectivity inside the reservoir. Larger grouting range is achieved under lower in-situ stress, lower hydrate saturation or with lower viscous grout. The split grouting capacity can be enhanced with the increase of wellbore size or multiple wells. The results could help to deeply understand the grouting pattern and veins morphologies in natural gas hydrate reservoirs during split grouting and construct potential reservoir stimulation strategies.