Theoretical investigation of the energy transfer efficiency under percussive drilling loads

With the deepening of oil and gas exploration, high performance drilling is required in these hard rocks now being penetrated. It is demonstrated that percussive drilling could promote the ROP (rate of penetration) effectively, and several impact drilling techniques have been applied to enhance the drilling performance. However, due to the various designs of rotary drilling tools as well as of working conditions, different shapes of stress waves would be generated during impact, which corresponds to different rate of penetration. The essence of percussive drilling is transmitting the impact energy in the form of stress wave, the objective of this research was to compare the energy transfer efficiencies of four different incident wave shapes, thereby providing theoretical guidance for the down-hole percussion drilling tool design. In this paper, the governing general equation of force-displacement was established in percussion drilling, and then the energy transfer efficiencies of four different incident wave shapes (exponent, rectangle, triangle, and sine) are calculated. Results show that 81% and 80% of the energy for rectangular and sine incident stress waves are used to break the rock, while for the triangular wave, only utilizes 41% of its energy to break the rock. Therefore, the research could contribute to the design of systems for percussive drilling of rock and lower cost drilling in the exploration of hard units.