Gas Production Enhancement from a Multilayered Hydrate Reservoir in the South China Sea by Hydraulic Fracturing

In this work, hydraulic fracturing was used for gas hydrate production at the second test site in the South China Sea for the first time. A multilayered hydrate reservoir model with low permeabilities was built on the basis of the field data obtained at this site, and artificial fractures were assumed to be created in the hydrate-bearing layer by hydraulic fracturing. Long-term simulations of the depressurization-induced gas hydrate production were conducted with a horizontal well, and the effects of the fractures on the enhanced gas recovery were thoroughly investigated. From the analysis of the simulation results, it can be known that the horizontal fracture could greatly promote the long-term production of natural gas from the reservoir, while the vertical branch fractures mainly contributed to the short-term gas recovery. By a combination of a horizontal fracture of 50 m with four branch fractures of 40 m, the long-term average gas production rate for a 1000 m long horizontal well was estimated to be 1.49 × 104 m3/day, and thus only two such horizontal wells were required to reach the level of the second Shenhu field trial (2.87 × 104 m3/day). This indicated that hydraulic fracturing was a promising technology for gas production enhancement from low-permeability clayey-silt hydrate reservoirs.