Reducing critical effects of torsional vibrations induced by PDC bits during rock destruction

Introduction. Torsional vibrations caused by drilling using a polycrystalline diamond compact (PDC) bit are analysed using wellbore data obtained under various drilling modes. The drilling caused by torsional vibrations are analysed. Two types of torsional vibrations, including those caused by the cutting action of a bit and by frictional forces.Aim. To investigate the induction of torsional vibrations as a result of rock destruction by PDC bits.Materials and methods. The research methodology was based on “Richard-Germay-Detournay” and “Tian-Detournay” bit designs and methods for reducing the critical effects of torsional vibrations induced by PDC bits during rock destruction.Results. Statistical analysis has shown that the drilling efficiency of the bit (DE) correlates well with the occurrence of torsion vibrations caused by the bit. The aggressiveness of the cutting structure of the PDC bit can be represented by an average DE rating. If the PDC bit is designed so that its DE exceeds a critical value, then the occurrence of torsion vibrations on the bit is unlikely during drilling.Conclusion. When drilling with a polycrystalline diamond PCD bit, two types of vibrations occur. If torsional vibration occurs due to the cutting action of the bit, then the fight against this process is focused on the design of the bit and operational parameters, the load on the bit and the speed of rotation of the bit. If the torsional vibration is caused by friction, vibration reduction methods should be focused on changing the design of the BHA and the drill string or the profile of the well. Therefore, it is very important to determine whether the torsional vibration is caused by the friction force of the elements, the cutting action of the bit, or both. In drilling, it is always necessary to search for the maximum penetration speed by changing the load on the bit under specified drilling conditions. To do this, it is necessary to evaluate the drilling efficiency of the DE bit, therefore, this article has evaluated the parameter depending on the size of the bit, which will determine the critical value of the drilling efficiency parameter.