Abstract：
Natural gas hydrate is a potential alternative source of energy for the future, and improving the extraction efficiency
is of great significance to promote its industrial development. In this study, productivity simulation of natural gas hydrate by
radial well depressurization and vertical well depressurization is studied with the use of HydrateResSim. This numerical model
was developed for thin layers of Class 3 hydrate reservoirs with closed boundaries. By comparing the changes of temperature,
pressure and hydrate saturation during gas production by a vertical well and a four-branch radial well, the reservoir stimulation
mechanism of radial wells is investigated. We find that depressurization through radial wells can significantly reduce the seepage
resistance in the near-well area and increase the effective drainage area. Besides, radial wells can promote the propagation of
pressure drop to the inside of the reservoir, which expands the region of hydrate dissociation and slows down the secondary
formation of hydrate. The decomposition of hydrate is an endothermic process. Therefore, the low temperature area generated
in the hydrate extraction process by a radial well has a larger range and has a more significant temperature drop. Under the same
pressure drop, radial wells’ cumulative gas production exceeds 250 thousand cubic meters during 1,000 days’ production, which
is more than three times that of the vertical well. The cumulative gas-to-water ratio of the radial well exceeds 60, which is about
twice that of the vertical well. Results show that radial wells can significantly improve hydrate recovery efficiency, which helps
to promote the commercial exploitation of hydrates in the South China Sea.
