Simulation of complex fracture network propagation and its application for shale gas reservoir

The commercial profit of shale gas is greatly controlled by the enhancement of matrix super-low permeability through effective reservoir volume stimulation. The resultant complex fracture network is composed of hydraulically induced fractures and natural fractures, while classical fracturing model based on the assumption of a symmetrical bi-wing fracture system is inapplicable for simulating relevant geometrical parameters. The stimulated shale volume is divided into fractures and matrix by referring to the theory of dual-media reservoir. This study assumes an elliptical stimulated volume and builds the whole complex fracture network with primary and small-scale secondary fracture networks. Geometrical parameters of primary fractures are computed using pseudo three fracturing model and secondary fracture parameters are simulated using elliptical equation. The mathematic model is programmed and applied for stimulation in Piceance shale gas reservoir in the U.S.A. The simulation data show high consistency with in-situ data. The larger the Young's modulus, the smaller the horizontal stress difference; the lower the viscosity of fracturing fluid, the greater the ratio of elongation, and the larger the simulated volume of the whole reservoir. Horizontal stress difference is most sensitive factor controlling the stimulated reservoir volume. Although sparser distribution of natural fractures means a larger stimulated reservoir volume, the effectiveness of stimulation is doubtful due to sacrificed complexity of the fracture network. This study provides a strong support for fracturing design and production prediction in shale gas reservoirs after fracturing stimulation. ©, 2014, Science Press. All right reserved.