Shockwave and plasma assisted rock cracking for geothermal drilling

Geothermal energy is a form of renewable energy derived from the heat stored within the Earth. It is harnessed by capturing heat from the Earth's interior by drilling through the earth where abrasive and hard rock formations are frequently encountered. Hard rock drilling poses a major challenge to geothermal energy extraction due to its poor rate of penetration, high-rate tool wear, non-productive time, wellbore instabilities, and circulation loss. Here, we report on a novel hybrid drilling approach which combines low energy pulsed electrical plasma and traditional drag type drilling, where the pulsed plasma partially fractures the rock prior to drilling. We demonstrate that micro-cracks initiated from the pulsed discharges (∼80 J/pulse) around the shock/plastic wave impacted area extend up to 9.4 mm into the material, reducing the specific cutting energy up to 56 % in granite. Rock cracking with low energy pulsed plasmas at elevated pressures (300 atm) is also demonstrated. We also outline and demonstrate a conceptual design of the hybrid drill bit with downhole energy conversion components without the use of electrical transmission from the surface. This low power hybrid pre-cracking method can provide viable access to renewable geothermal energy and fossil fuel reservoirs where high compressive strength rocks are encountered.