Gas recovery from silty hydrate reservoirs by using vertical and horizontal well patterns in the South China Sea: Effect of well spacing and its optimization

Low productivity is the key to restrict the commercial development of hydrates. Due to the advantage of integration, the multi-well pattern is a promising way to obtain high gas recovery rate. Here, the vertical and horizontal well patterns with different WSs are designed under some possible reservoirs in the South China Sea. Then, the production behaviors of these well patterns are compared and the optimal WS is determined in both well patterns by numerical simulation. The results show that the relatively longer WS in homogeneous sediments with the same ultra-low permeability means the lower cumulative gas recovery, but the full opposite phenomenon will be observed after increasing the formation permeability. The exponential model can characterize the relationship between cumulative gas recovery and WS no matter which well pattern is employed, and the optimal WS can be determined by the minimum radius of curvature method. As for the relatively high-permeability reservoir confined by the ultra-low permeability burdens, the gas recovery will increase in both well patterns, but this stimulation may gradually weaken in the long-term production. The ideal WS can be suggested by the comparative law of cumulative gas recovery during each stage, which can give valuable reference for future application.