Damage-Failure Characteristics and Energy Evolution Laws of Reservoir Rock with Irregular Hydraulic Borehole under Uniaxial Compression

High Resolution Image Download MS PowerPoint Slide The stability of hydraulic boreholes formed by water jet drilling is critical for efficient oil and gas extraction, yet existing research predominantly focuses on mechanically drilled circular boreholes, leaving a significant gap in our understanding of the stability mechanisms of irregular hydraulic boreholes. These irregular shapes, characterized by nonuniform stress distributions and potential wall damage, pose substantial risks to the long-term stability. This study introduces roundness ( e ) to quantitatively characterize the morphological integrity of the hydraulic boreholes. The quantitative relationship between nozzle parameters and borehole roundness was established, where roundness increases exponentially with the number of rear nozzles but at a diminishing rate. Through integrated PFC numerical simulations and theoretical analysis, the influences of borehole roundness and wall damage on the stability and energy evolution of reservoir rock with irregular hydraulic boreholes under uniaxial compression were investigated. Stress–strain analysis revealed four distinct deformation stages, including compaction, elastic, plastic, and postpeak, with higher-roundness boreholes exhibiting stable crack propagation and greater peak stress compared to low-roundness rock specimens. Acoustic emission (AE) monitoring showed that the total number of AE events decreases by 24.4% as roundness increases from 0.89 to 0.996, while the elastic modulus improves exponentially, confirming the role of roundness in enhancing mechanical performance. Energy evolution analysis shows that dissipated energy increases more gradually in high-roundness boreholes, whereas low-roundness specimens exhibit abrupt energy release and brittle failure characteristics. The proposed energy-based damage constitutive model accurately captures the stress–strain behavior, validating the integration of roundness as a key stability indicator. These findings could provide a theoretical basis for optimizing hydraulic borehole design, with direct implications for improving safety and efficiency in oil–gas extraction engineering.