Abstract:

The bit profile of a downthehole drill bit is optimized to improve rockdrilling efficiency. Through a split Hopkinson pressure bar(SHPB) test, spherical, tapered, and pickshape drill bits are employed to drill gray sandstone, red sandstone, and marble with different loads, respectively, and peak stress, input energy, and energy dissipation rate variation trends under different incident energies are compared and analyzed. The findings are summarized as follows: (1) The peak stress, dissipated energy, and energy dissipation rate in SHPB test can be used as indexes to estimate the drilling performance of a drill bit. (2) For soft rocks, e.g., gray sandstone and marble with welldeveloped joints, it is suggested to increase the input energy of the bit to improve the energy dissipation rate. For hard rocks, e.g., red sandstone, the input energy must be set according to the drilling speed because increased input energy has negligible effect on improving energy dissipation rate. (3) Under limited drilling power conditions, the pickshape drill bit is recommended to reduce the impact force and impact power required by rock crushing. (4) Relative to drilling speed and cost, a tapered drill bit is preferred to improve dissipation energy and energy dissipation rate.

Key words: downthehole drill bit, drill bit profile, split Hopkinson pressure bar test, peak stress, energy dissipation rate, rockdrilling performance