Evaluation of the gas production enhancement effect of hydraulic fracturing on combining depressurization with thermal stimulation from challenging ocean hydrate reservoirs

The stimulation of hydraulic fracturing on a combination of depressurization with thermal stimulation for natural gas hydrate (NGH) exploitation from challenging ocean hydrate reservoirs is investigated in this study. The influence of fracture permeability, well spacing on hydrate exploitation, and the enhancement effect of hydraulic fracturing on different well spacing are numerically investigated. The results show that the hydraulic fracturing has a significant improvement on hydrate exploitation performance, including hydrate decomposition behaviour, gas production behaviour, gas recovery ratio, and energy ratio. This improvement enhances with the increase of fracture permeability, but the corresponding rate of increase gradually decreases. Gas production performance is extremely sensitive to well spacing. An extremely low gas production volume, gas recovery ratio and energy ratio will be obtained when well spacing is excessive. The existence of fracture can increase the effective well spacing. After fracturing, the gas production performance of each well spacing are significantly improved and this improvement performs better with larger well spacing.