Numerical simulation of the development of hydrate-bearing layers by depressurization of radial wells

A perpendicular bisector unstructured grid was used for meshing a model with radial wells, and the non-orthogonal correction of the flux calculation was implemented in the Tough+Hydrate software. A numerical simulation model was established based on the geological parameters of hydrate-bearing layers (HBLs) in the Shenhu area of the South China Sea. Gas and water production from the HBL, developed through depressurization of radial wells, was studied, and factors influencing gas production were analyzed. The findings indicate that employing radial wells in both hydrate and mixed layers significantly accelerated gas and water production in the HBL, facilitating rapid depressurization. Faster depressurization, in turn, promoted the dissociation of natural gas hydrate (NGH) and increased gas production. Cumulative gas production using radial wells in double layers increased by 110.03% compared with a horizontal well. In the later stage of depressurization development, NGHs in the mixed layer were almost entirely dissociated, whereas nearly three-quarters of NGHs in the hydrate layer remained undissociated. The combined method of depressurization and thermal stimulation is expected to further promote NGH dissociation and enhance gas production. Analysis of influencing factors revealed that higher gas production was associated with a greater number of laterals and larger lateral length, whereas the layout of the laterals had little effect on performance.