Electropulse stimulation provides a means to fracture hard rocks into small fragments with the use of high-voltage electric pulses. As these techniques offer a frictionless method to break rock in tension, they have the potential to improve drilling, processing and excavation by reducing energy requirements and decreasing equipment wear. However, to date, descriptions of the processes involved in hard-rock electropulse stimulation remain largely empirical in nature – concentrating on the macroscopic effects of the electrical discharges, rather than their underlying causes.
Results from a recent series of experimental studies and associated numerical models investigating the effects of electropulse stimulation on hard rock at the grain scale are outlined in this paper. The effects of the electric pulse treatments on the rock microstructure and the nature of the fragmented particles produced are also described. These results are compared with numerical simulations that track the path and effect of the voltage pulse on the rock mass. The implications of these results on the performance of electropulse methods are discussed for a range of operating conditions and rock-types.
Electropulse stimulation involves the use of high voltage pulses to break rocks into small fragments. A short duration (typically on the order of microseconds) high voltage current is transmitted through the rock, causing local heating along the conductive pathway. The induced heating in turn results in the growth of fractures due to the thermal expansion of the mineral grains and pore fluids.
Hard rock drilling is an emerging application of electropulse stimulation. Electropulse methods have the potential to be faster than mechanical drilling and involve no moving parts, thereby reducing equipment wear and tripping time. High voltage pulses have been used to break ore in the laboratory since the 1950s and 1960s (Andres 1977, Lisitsyn et al 1998). However, it is only recently that working prototype electropulse drills have been developed, thanks to advances in downhole electronics technology. These drills have shown promising improvements in drilling rates for hard rocks under laboratory conditions (Anders et al 2017), yet they remain untested at depth.