Abstract:

In order to explore the characteristics of fracturing fractures of shale with weak plane development, a fracture propagation model of shale reservoirs taking the weak plane of bedding and natural fractures into account is established by the three dimension discrete element method to analyze characteristics of fracturing fractures under different injection rates, fracturing fluid viscosity, bedding tensile strength and natural fracture cohesion. The research results show that the high-displacement injection and high fracturing fluid viscosity can reduce the restriction of near-wellbore bedding on hydraulic fractures and increase the ability of hydraulic fractures to penetrate layers. The hydraulic fractures can continuously pass through six beddings when the fracturing fluid viscosity is increased to 10 mPa·s. The tensile strength of the bedding connected to the natural fracture is not the main factor affecting its own opening. The greater the natural fracture cohesion is, the greater the natural fracture shear strength and the lower the degree of opening of natural fracture will be. When bedding and natural fractures develop near the wellbore, the hydraulic fractures can be fully extended by increasing the injection rates and the fracturing fluid viscosity in the early stage. For shale which is easy to form simple double-wing fractures, pumping an appropriate amount of acid in the early stage can dissolve the natural fracture filler, so as to reduce the natural fracture cohesion, increase its opening degree, and improve the complexity of fractures.

Key words: shale, bedding, natural fracture, fracture propagation, discrete element method