Modeling Percussion and Rotary Percussion Drilling in Strong Rocks.

The article describes two single-mass models of a drill string and different methods of bottom-hole treatment: percussion and rotary percussion. The loads created by the piston are transferred to rocks via a progressively advancing bit in the first model and via a rotatable bit in the second model. The drag force applied to the bit is found from the nonlinear dependence on the penetration rate and kinematic parameters which govern the force impact on the rock and its loss of strength: initial blow velocity and rotational speed modulus of the bit. The optimal initial blow velocities are found at the preset blow frequency; they ensure elimination of short-term stick slips in penetration of the bit. For the mentioned cases of penetration, the processes of percussion and rotary percussion drilling in strong rocks are provided with the strict mathematical description. The numerical modeling results are presented. [ABSTRACT FROM AUTHOR]