Fracture network complexity of tight sandstone and its influencing factors

The fracture network complexity analysis of tight sandstone plays an important role in hydraulic fracturing optimization, fracture network prediction and fracture modeling. Based on the experimental study on the dynamic evolution process and main controlling factors of complex fracture network in sandstone, the complexity analysis of fracture network is carried out by deeply discussing the fractal and multifractal spectrum characteristics of fracture network. The results show that the initiation and propagation of cracks run through the whole process of stress-strain, and the complexity of fracture network is mainly controlled by its own microscopic fabric characteristics, and has obvious scale and confining pressure effects. The fractal dimension of the three-dimensional fracture network and the average spectral width of the multifractal spectrum can represent the complexity and heterogeneity of the spatial distribution of the fracture network, respectively. The higher the content of quartz, feldspar and other brittle minerals in sandstone, the larger the porosity and the smaller the particle size, the more complex the spatial distribution of fracture network and the weaker the heterogeneity. Clay minerals are not conducive to the formation of complex fractures. The larger the compressive strength and elastic modulus, the more complex the spatial distribution of the fracture network and the weaker the heterogeneity.