The Use of Advanced Percussion Drilling to Improve Subsurface Permeability for Enhanced Geothermal Systems

摘要

Subsurface permeability is typically enhanced in current EGS developments by injecting high volumes of fluid at pressures that will open pre-existing natural fractures or weaknesses in the rock. A few existing stimulation technologies that do not use water have been developed and applied with some success. These technologies include pneumatic or compressed air fracturing, propellant fracturing, and explosive fracturing. However, given the limitations of existing technologies, alternative technologies must still be discovered to cost effectively stimulate geothermal resources in a controlled manner, without the use of high volumes of fluids. One promising technology is percussion fracturing. We investigated the use of advanced percussion fracturing technology to stimulate and enhance permeability in hot rock for EGS development without large water volume usage. A preliminary review and characterization of the fundamental rock mechanical processes associated with percussion fracturing was first studied. Next, a 3D numerical model was developed for the percussion drilling process to study the impact of dynamic stress waves generated by percussion drilling at the borehole face. This leads to estimates of the damage and fracture extent away from the wellbore, as a function of input energy and relative application of dynamic shear and compression loading at the wellbore. Our preliminary research results show that permeability improves in the near wellbore region. We conclude that this novel stimulation technique can enhance the feasibility for application of EGS, thereby supporting the growth of a renewable, clean energy technology while increasing our domestic energy production.