Class-III Hydrate Reservoir Depressurization Production Enhancement by Volume Fracturing and Cyclic N₂ Stimulation...

The depressurization effect is limited to class III hydrate reservoir recovery. To improve the depressurization effect, a new method of volume-fracturing and cyclic N₂ stimulation combination (VFCS) was proposed. The production performance of this method was investigated by using numerical models based on reservoir parameters of the SH7 hydrate site in the South China Sea. The results show that (1) VFCS can greatly enhance the production performance with the average CH₄ production rate being approximately 2.85 times higher than that of pure depressurization. This method combines the effects of volume fracturing and cyclic N₂ stimulation by improving the seepage environment and further reducing the CH₄ partial pressure in the gas phase. (2) High reservoir permeability, medium hydrate saturation, large volume-fracturing scale, low bottom-hole pressure, and high N₂ injection amount can increase CH₄ production by VFCS. (3) Although VFCS has the largest CH₄ production volume and the highest hydrate dissociation degree among the studied production strategies, the reservoir temperature drop is significant by VFCS and future studies can be focused on the external heat supply to the reservoir to further improve the production.