Enhancing Gas Production via Combined Hydraulic Fracturing and Depressurization in a Hydrate Reservoir Underlain by Free Gas, South China Sea

The gas production rates of recent hydrate production tests remain below the commercially viable threshold. To enhance the gas rate, a combined method of hydraulic fracturing and depressurization was proposed for a reservoir containing hydrate and free gas layers. The model was initially validated against the gas production rate from the second offshore Shenhu production test in the South China Sea. Subsequently, the production rate by hydraulic fracturing and depressurization in a horizontal well was investigated. Results indicate that horizontal well deployment in the three-phase layer (TPL, including hydrate, gas, and water) achieves the highest gas rate, while a similar gas rate is observed for the free gas layer (FGL), and the least rate is observed for the hydrate-bearing layer (HBL). The fracture significantly boosts the gas and water production rates, especially in the early stage. However, similar gas rates are observed later for TPL and FGL due to the presence of a band of free gas flow. The well deployment in the TPL is the optimal option because of low water production, whether fractures are present or not. A vertical fracture has a less significant impact on enhancing gas and water production compared with that of a horizontal fracture. The influence of fracture length and number is negligible for wells in the TPL but considerable in the HBL. Implementation of fracturing technology could reduce the number of required horizontal wells by over 33%. This methodology is pivotal for the commercial exploitation of the hydrate reservoirs.