First Offshore Gas Hydrate Production Test in the South China Sea: Numerical Simulation of Production Behavior with Different Multicluster Well Patterns

Multicluster wells are critical for the commercialization of natural gas hydrate (NGH). Based on the on-site data of the first natural gas hydrate trial production in the South China Sea, a numerical model was constructed. The key parameters, including well spacing and well-net patterns, were investigated. Under the preconditions of a fixed well-net pattern of four wells and continuous production for 1080 days, the results show that as well spacing increases from 20 to 60, 100, 140, and 180 m, respectively, productivity increases to 136.3, 169.7, 190.3, and 198.4% with a pressure difference of 2 MPa and 128.4, 158.6, 185.2, and 198.6% with a pressure difference of 6 MPa. The rate of production rise does not increase linearly, and the free gas tends to be trapped in the middle of the multicluster well, causing the "blind zone" phenomenon with increasing well spacing. Under the preconditions of fixed well spacing (60m) and pressure difference (6 MPa), with the number of wellbores increased from 2 to 9 in the well-net patterns, the productivity increases to 124.2, 131.8, 148.2, 158.1, 177.3, 201.9, 208.3, 244.4, and 250.3%, respectively, and the productivity increase is synchronized but not linear, and the increase ratio becomes smaller. Under the CVW15 well-net patterns, when the well spacing is set to 180m, it is estimated that 18 groups of well net can achieve commercial production, which provides a reference for well-net pattern selection and parameter setting for NGH production.