Gas Production Enhancement by Horizontal Wells with Hydraulic Fractures in a Natural Gas Hydrate Reservoir: A Thermo-Hydro-Chemical Study

Itis a complicated thermo-hydraulic-chemistry (THC) coupling processto produce methane from a natural gas hydrate (NGH) reservoir. Tomeet the commercial exploitation of NGH, hydraulic fracturing hasbeen proposed to increase gas production. In this study, a THC couplingmethod was set up to simulate the NGH production process. Based onthis coupling method, a series of three-dimensional models were builtto model the NGH production by the depressurization method througha combination of horizontal well and hydraulic fracturing. The influencesof factors (fracture length, fracture aspect ratio, fracture number,fracture interval, production pressure, and instinct permeabilityanisotropy) on the stimulation efficiency were analyzed. The resultsindicated: (i) the combination of horizontal well and hydraulic fracturingcan greatly improve gas production comparing with only the horizontalwell and the long-term folds of increase (FOI) > 5. (ii) The stimulationefficiency increases with the increase of fracture length. Properlyincrease the fracture number and/or the fracture interval can obviouslyincrease the stimulation efficiency of fracturing and extend the periodof first stage of FOI (FOI >= 10). (iii) For the same fracturewidth, the fracture section area is the most significant geometryfactor, affecting the gas production improvement in hydraulic fracturing.When the fracture section area is specified, the effect of fractureaspect ratio on FOI is neglectable. (iv) The FOIs are almost the samewhen the production pressure changes under the same fracture parameter.(v)There exists an obvious interference between adjacent fractures, whichincreases with the increase of fracture half-length and/or the aspectratio between the half fracture length and half fracture height underthe same fracture interval. This work provides theoretical suggestionsfor hydraulic fracturing of horizontal well in NGH production.