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

Abstract

It is a complicated thermo-hydraulic-chemistry (THC) coupling process to produce methane from a natural gas hydrate (NGH) reservoir. To meet the commercial exploitation of NGH, hydraulic fracturing has been proposed to increase gas production. In this study, a THC coupling method was set up to simulate the NGH production process. Based on this coupling method, a series of three-dimensional models were built to model the NGH production by the depressurization method through a combination of horizontal well and hydraulic fracturing. The influences of factors (fracture length, fracture aspect ratio, fracture number, fracture interval, production pressure, and instinct permeability anisotropy) on the stimulation efficiency were analyzed. The results indicated: (i) the combination of horizontal well and hydraulic fracturing can greatly improve gas production comparing with only the horizontal well and the long-term folds of increase (FOI) > 5. (ii) The stimulation efficiency increases with the increase of fracture length. Properly increase the fracture number and/or the fracture interval can obviously increase the stimulation efficiency of fracturing and extend the period of first stage of FOI (FOI ≥ 10). (iii) For the same fracture width, the fracture section area is the most significant geometry factor, affecting the gas production improvement in hydraulic fracturing. When the fracture section area is specified, the effect of fracture aspect ratio on FOI is neglectable. (iv) The FOIs are almost the same when the production pressure changes under the same fracture parameter. (v) There exists an obvious interference between adjacent fractures, which increases with the increase of fracture half-length and/or the aspect ratio between the half fracture length and half fracture height under the same fracture interval. This work provides theoretical suggestions for hydraulic fracturing of horizontal well in NGH production.