Simulation Method for the Distribution of Fractured Branches in Tight Reservoirs During CO2 Fracturing Based on a Fractal Method

The accurate description of fracture distributions is a crucial prerequisite for fracturing design and the evaluation of fracturing effects in tight reservoirs. We employed a fractal L-system to establish a tree branch model and derived a planar simulation method to characterize the distribution of natural weak discontinuities in rock. Weak discontinuities are classified using fractal similarity principles, enabling the determination of shear and opening criteria for weak discontinuities at various levels in water-based and CO2 fracturing, as well as the pressure drop gradient within fractures after the initiation of weak discontinuities. Based on a weak discontinuity distribution model and fracture criteria, a simulation calculation method for the distribution of fracturing branch fractures was formulated. The results indicate that the number of branch fractures is closely related to the net pressure within the fractures at the wellbore and the difference between the maximum and minimum principal stresses in the reservoir. Compared with water-based fracturing fluids, CO2 fracturing can facilitate the opening of branch fractures by reducing the opening conditions required for them to occur. The proposed calculation method can generate planar fracture morphologies and opening conditions with fractal characteristics, providing a basis for studying complex fracture formation mechanisms during CO2 fracturing in tight reservoirs.