The flow field characteristics and rock breaking ability of cone-straight abrasive jet, rotary abrasive jet, and straight-rotating mixed abrasive jet

Radial jet drilling (RJD) technology is expected to be a technology for the efficient exploitation of geothermal resources. However, the low rock-breaking efficiency is the major obstacle hindering the development of RJD technology. The flow field characteristics and rock breaking ability of cone-straight abrasive jet, rotary abrasive jet, and straight-rotating mixed abrasive jet are analyzed by numerical simulations and experiments. Results show that the axial velocity of the cone-straight abrasive jet is high, the tangential velocity is basically zero, the radial velocity is also small, and the jet impact area is concentrated in the center. A deep hole with a diameter of only 25 mm is formed when the cone-straight abrasive jet breaks the granite. Due to the presence of the guiding impeller, the rotary abrasive jet basically has no axial velocity and has the highest tangential and radial velocity, so it can break the granite to form a hole with a diameter of about 55 mm and a central bulge. The straight-rotating mixed abrasive jet has a large axial/tangential/radial velocity at the same time, so it can break the granite to form a hole with a diameter of about 52 mm with a low bulge. The results show that the straight-rotating mixed abrasive jet combines the advantages of the cone-straight jet and the rotary jet, and is more suitable for the RJD technology. The research results can provide reference for the development of efficient rock-breaking and hole-forming technology, and promote the development of RJD technology in the field of geothermal development.