Numerical and experimental investigation on hydraulic-electric rock fragmentation of heterogeneous granite

Abstract

Hydraulic-electric rock fragmentation (HERF) plays a significant role in improving the efficiency of high voltage pulse rock breaking. However, the underlying mechanism of HERF remains unclear. In this study, considering the heterogeneity of the rock, microscopic thermodynamic properties, and shockwave time domain waveforms, based on the shockwave model, digital imaging technology and the discrete element method, the cyclic loading numerical simulations of HERF is achieved by coupling electrical, thermal, and solid mechanics under different formation temperatures, confining pressure, initial peak voltage, electrode bit diameter, and loading times. Meanwhile, the HERF discharge system is conducive to the laboratory experiments with various electrical parameters and the resulting broken pits are numerically reconstructed to obtain the geometric parameters. The results show that, the completely broken area consists of powdery rock debris. In the pre-broken zone, the mineral cementation of the rock determines the transition of type C_Ⅰ cracks to type C_Ⅱ and type C_Ⅲ cracks. Furthermore, the peak pressure of the shockwave increased with initial peak voltage but decreased with electrode bit diameter, while the wave front time reduced. Moreover, increasing well depth, formation temperature and confining pressure augment and inhibit HERF, but once confining pressure surpassed the threshold of 60 MPa for 152.40, 215.90, and 228.60 mm electrode bits, and 40 MPa for 309.88 mm electrode bits, HERF is promoted. Additionally, for the same kind of rock, the volume and width of the broken pit increase with higher initial peak voltage and rock fissures will promote HERF. Eventually, the electrode drill bit with a 215.90 mm diameter is more suitable for drilling pink granite. This research contributes to a better microscopic understanding of HERF and provides valuable insights for electrode bit selection, as well as the optimization of circuit parameters for HERF technology.