Research progresses in formation mechanism of complex fracture network for unconventional reservoir

The practice of oilfield development promotes the development theory, and the breakthrough of development theory brings about the revolution of development technology. Using horizontal wells and volume fracturing technology, volume fracturing has been applied in unconventional reservoir, and the formation mechanism of complex fracture network will bring innovation to development technology. At present, the research on the formation mechanism mainly focuses on theoretical research, experimental research, and numerical simulation. Theoretically, the mechanical model of the intersection of HF and NF is established, and some judgment criteria are put forward. Activation of NF by HF is a necessary condition for the formation of complex fracture networks; the activation conditions of NF are verified by true triaxial experiment in terms of horizontal stress difference, approximation angle, and fracturing fluid viscosity; finite element method, finite difference method, boundary element method, and discontinuous displacement method have their own advantages and disadvantages on simulation. Using digital speckle correlation technique, the authors explained the mechanism of shear action on the formation of fracture network, established a macro-meso two-scale non-uniform damage constitutive model, and formed a computing method for dynamic expansion of fractured network in tight reservoir. A field well example is calculated using this method.