Influential mechanism of perforation parameters in geothermal fixed-plane perforation recovery

The fixed-plane perforation technology, which is derived from oil and gas production, offers remarkable advantages in inducing fracturing and increasing fracture volume, but its theoretical foundation incompatible with the practical application of hot dry rock (HDR). In this study, a coupled thermal–hydraulic–mechanical model is developed to reveal the influence of perforation parameters on fracturing results in an environment of HDR. The stress, temperature distribution and damage volume of the rock at different numerical levels of the perforation parameters are compared to characterize the mechanism of the effect of perforation parameters on the fracturing results. Under the experimental conditions, the results of the control experiments show that the EGS system achieves a high techno-economic performance when the injection angle is about 45°, the injection density is about 5 clusters/m, and the injection depth is about 2.0 m. The analysis of orthogonal results not only reveals the time-varying sensitivity of rock cracking to perforating parameters, but also reveals that the in-plane perforation spacing is crucial to the effect of perforating parameters on fracturing. The analysis of variance also indicates that the degree of influence of perforation parameters on fracture varies over time. The area of the perforation wall defines the fracturing efficiency in the early stage of fracturing; the volume of fluid-rock interaction space, determined by in-plane perforation spacing, controls the fracturing efficiency in the later stage of fracturing. The results of the orthogonal analysis considering the interactions demonstrate that the interactions between the perforation parameters have a negligible effect on the fracturing results compared to the perforation parameters. This research can be utilized to optimize perforation parameters for fixed-plane fracturing.