Hydraulic fracturing is an effective approach to bring economic productions for unconventional gas reservoirs. A numerical model is developed to model the complex fracture network after hydraulic fracturing. Particular treatments for full-tensor effects and fractures of different scales are integrated in the method to deliver fast evaluating the effect of hydraulic fracturing on recovery of unconventional gas reservoirs.

A discrete fracture model of the complex fracture network is firstly built up as the high-resolution reference model. Then numerical simulation grids are determined according to the fracture scales, fracture distribution and well locations. During numerical simulation, primary hydraulic fractures are treated explicit as the reference model, while relatively small-scale hydraulic fractures and natural fractures are upscaled into dual porosity grids by global upscaling procedures under multipoint flux approximation scheme. An integrated output least squares method, which aims to minimize the total bias of simulation results, is adopted to obtain the optimal transmissibility connection list of the simulation model.

An application case is designed to validate the proposed method. The results show that the proposed model can improve the computational efficiency for predicting the effect of hydraulic fracturing, and can maintain an equivalent numerical precision at the same time. This model can serve as a reliable tool for fast evaluating of different plans in hydraulic fracturing of unconventional gas reservoirs.

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