Investigation of PDC Cutter Structural Integrity in Hard Rocks

Robustness of round and V-shaped polycrystalline diamond compact (PDC) cutters against mechanical and thermal load was evaluated. Forensic analysis was used to estimate the range of loads and depths of cut (DOC) that cause structural overload of PDC cutters. Finite-element analyses (FEAs) were calibrated against these data and used to estimate the integrity of cutters. Thermal-abrasive wear was tested with single cutter tests on Sierra White granite with and without cooling for multiple material grades. The axial and tangential impact resistances were evaluated with drop and front face impact tests. In addition, full-scale laboratory drilling tests were conducted in granite [unconfined compressive strength (UCS) = 28,000 psi] and quartzite (UCS = 56,000 psi). Finally, failures for round and V-shaped cutters were evaluated in field trials. The V-shaped cutters scored similar to baseline cutters in thermal-abrasive tests but lower in axial impact tests. They also failed at 13 to 18% lesser tangential load. By accounting for 16% reduction in contact area between the shaped cutter and load anvil, it was concluded that both cutter geometries fail essentially at the same stress. In all full-scale tests, round cutters failed before the shaped cutters. This was in contrast with drop tests and is attributed to the shaped cutter's cutting efficiency, resulting in lesser load on the cutters for the same rate of penetration (ROP). The results were compared with field runs in hard and interbedded application in Oklahoma and west Texas. The conclusion based on FEA, laboratory, and field data was that in most cases, this shaped cutter shows the same or better dull as its base grade.