The multifracture competitive initiation under different fracturing modes is of great significance for designing hydraulic fracturing treatments. In this paper, a numerical model of shale oil reservoir fracturing considering fluid-mechanics coupling is established based on a three-dimensional (3D) discrete lattice method, and the properties of shale are characterized by the combination of rock matrix and weak mechanical layer. In addition to comparing the formation mechanism of complex fractures under conventionally oriented perforation and spiral perforation, radial well fracturing is also specifically considered. Furthermore, taking spiral perforation as an example, the influences of perforation phase, diameter, and density on near-wellbore fracture propagation are further analyzed. The results show that radial well fracturing can significantly reduce fracture initiation pressure and obtain a larger fracture area than perforation fracturing. For the perforation fracturing, the near-wellbore fracture morphology of oriented perforation is single, mainly forming multiple parallel planar fractures. Near-wellbore fracture morphologies of spiral perforation are complex and varied, including single planar fractures, single spiral fractures, double spiral fractures, and stepped spiral fractures. Appropriately decreasing the perforation phase and increasing the perforation diameter and density can reduce the number of failed perforations and promote the interconnectivity of fractures, thus forming the main fracture that communicates multiple perforation tunnels. The accuracy of the model is further verified by laboratory experiments under the same conditions as those of the numerical simulation. The results can provide theoretical guidance for the optimization of the fracturing parameters in shale oil reservoirs.
Gu et al. (Thu,) studied this question.