Fracture network stimulation effect on hydrate development by depressurization combined with thermal stimulation using injection-production well patterns

Highlights: • A fracture network-assisted hydrate mining scheme is firstly proposed. • Horizontal fractures significantly improve mining while the vertical is useless. • Water breakthrough of production wells severely inhibits hydrate mining behaviour. • Fracture spacing converts hydrate dissociation mode, dramatically impacting mining. In this study, the stimulation effect of the fracture network on hydrate development by depressurization combined with hot water injection (D + T_iw) utilizing injection-production well patterns was explored and the key fracture properties' influences on stimulation effect were investigated. The results showed that D + T_iw significantly improved hydrate decomposition, but has a minimal enhancement on CH₄ production owing its extremely low CH₄ recovery ratio. The fracture network improved CH₄ production of D + T_iw significantly. Water breakthrough of production wells has a strong influence on D + T_iw development performance; and, divided the influence of fracture conductivity on hydrate development into two opposite stages. The change in fracture spacing caused a hydrate decomposition mode transformation. Under larger fracture spacing, hydrate decomposition occurred in the piston-like decomposition mode and the effect of fracture spacing on hydrate development performance was minimal. However, when fracture spacing was small enough to transform the hydrate decomposition into a non-piston-like decomposition mode, hydrate decomposition and CH₄ production rate increased sharply.