Numerical Simulation of the Influence of the Perforation on the Initiation Geometries of Hydraulic Fracture in HDR Reservoirs

Hot dry rock (HDR) is a type of clean and abundant energy. Hydraulic fracture (HF) geometry is crucial for the exploitation of HDR. Perforation mode and stress type significantly affect the HF initiation geometry. However, due to the high temperatures, low permeability, and tight geomechanical properties of HDR reservoirs, the influence of perforation on the HF geometry of HDR under different stress types remains unclear. The extended finite-element method (XFEM) is a promising method to simulate HF propagation. This study investigates the effects of perforation mode and three stress types on HF initiation geometry in vertical wells. A new method for evaluating HF geometry is proposed. The results show that HF complexity increases progressively from oriented to planar to helical perforations. HF geometries are strongly controlled by perforation modes. Perforation orientation determines the initial HF direction. The HF propagation direction and initiation pressure are governed by the in situ stress. When the minimum principal stress direction is perpendicular to the perforation orientation, the stress shadow effect significantly changes the HF geometry. For field operations, when both HF complexity and initiation pressure are considered, planar and helical perforations are identified as optimal for normal fault stress type. Meanwhile, helical perforation is considered most suitable for the thrust stress type. Both oriented and helical perforations are determined to be applicable to the strike-slip stress type. The results provide a basis for optimizing fracturing parameters in the actual exploitation of HDR.