Several phenomena that negatively affect drilling efficiency are still commonly observed in practice. These phenomena can often be linked directly to the high torque required for a PDC bit to aggressively shear formation, and the difficulty of effectively transmitting such torque consistently to the bit. In highly transitional or conglomerate formations, the depth of cut and subsequent torque required for the bit to continuously shear formation fluctuates greatly, leading to the buildup and release of torsional energy in the drill string, commonly known as stick/slip. High speeds and vibration during the slip phase, combined with the heterogeneous and/or hard nature of the environment can cause damage to PDC cutters and other drill string components, resulting in reduced bit and tool life as well as poor rate of penetration (ROP).
A proprietary torsional impact hammer was tested in applications in Western Oklahoma and in the Southeast Arabian Peninsula where drilling efficiency was believed to be much lower than the theoretical limit. These applications were identified by high cost per foot drilling with roller cone and diamond impregnated bits, as well as known and expected high vibrations accompanying unsuccessful and inconsistent PDC testing. The case studies reveal the strengths and weaknesses of applying such a solution, and introduce a discussion on selection of applications where this solution is advisable. The balance of this paper will also describe how this solution has reduced drilling costs and changed the economics of drilling applications in Western Oklahoma and the Southeastern Arabian Peninsula over the course of the cases studied.