Simulating fragmentation of hard granitic rocks during electropulse drilling

Drilling in hard rock constitutes a significant portion of the total cost associated with geothermal power plant operation. Conventional rotary-head drilling, however, is commonly associated with frequent equipment damage, leading to high drilling costs. Contact-less drilling technologies, such as electropulse drilling, are therefore being developed to improve drilling efficiency. Electropulse drilling uses repeated application of high-voltage pulses to fragment the rock mass. During each drilling pulse, the electric potential applied on the drill bit discharges through the solid rock mass. While experiments show the rupturing of the rock mass occurring during discharge, the physical processes leading to this rock damage are still poorly understood. We present a model for the coupled electro-mechanical processes responsible for rock fragmentation. Simulated are the passage of the pulse through the rock mass, electrical breakdown, and the mechanical behaviour on the grain scale. Different factors, such as rock composition, pulse duration and maximum applied voltage are considered. The presented model deepens understanding of the different electro-mechanical and operational factors required for successful electropulse drilling.