Abstract: Aiming at the problem of quantifying the composition of complex fracture network and fracture activation after shale volume fracturing, a complex fracture network model of weak surface of prefabricated structure is established based on finite element method, global embedded cohesive zone model and real shale outcrop. Considering the influence of fully coupled stress/fluid, the effects of weak plane azimuth, horizontal stress difference, fracturing fluid viscosity and displacement on fracture network composition, geometry and SRV are studied. The concept of fracture relative activation, which can quantitatively analyze fracture network composition and fracture activation, is proposed. The results show that the fracture geometry of two kinds of conjugated shale after compaction is controlled by the most weakly mechanical weak-plane, and the fracture network is respectively axisymmetric and centrosymmetric. The fracture network is composed of the weak-plane fractures with the dominant free gas transport and the matrix microfractures with the dominant adsorbed gas transport; the effects of weak-plane azimuth, horizontal stress difference and fracturing fluid viscosity on SRV length are not monotonous, while the increase of the azimuth, horizontal stress difference, fracturing fluid viscosity and the reduction of appropriate displacement will lead to the increase of SRV width; the effect of horizontal stress difference on the relative activation of fractures does not change monotonically, while the increase of weak-plane azimuth, fracturing fluid viscosity and displacement will lead to the increase of the relative activation of matrix microfractures, the increase of the total length of activated fractures and the decrease of the relative activation of weak-plane fractures.

Key words: shale, hydraulic fracturing, cohesive zone model, fracture relative activation, weak plane