Numerical simulation of gas recovery from natural gas hydrate using multi-branch wells: A three-dimensional model

Natural gas hydrate, a potential energy source, is clean and occurs abundantly in nature. Enhancing the gas production efficiency from gas hydrate-bearing sediments (GHBS) is of great significance to promote its industrial development. In this study, the radial jet drilling (RJD) technology is innovatively proposed to stimulate oceanic hydrate reservoirs. With an open-source simulator HydrateResSim, a 3D model is constructed based on the geological data from the SH7 site in the South China Sea. The hydrates exploitation performance using the combination of radial wells and depressurization is studied for the first time. Results indicate that radial wells can significantly enhance the gas production rate in the early stages of production. The hydrate recovery factor and the radial branch length are linearly related. However, the application of radial wells seems incapable of prolonging the gas production life cycle. By analyzing the multi-physical response of GHBS induced by depressurization, the stimulation mechanisms of radial wells are characterized as enlarged drainage area, enhanced pressure drop propagation, and increased geothermal heat flow. This work verified the capability of RJD in promoting hydrate extraction. Also, it provides insights into the potential applications of multi-branch wells in field trials of hydrate production. (c) 2020 Published by Elsevier Ltd.