This paper discusses a new and general method of backup-cutter layout to extend bit life without sacrificing rate of penetration (ROP) and two field-case studies. This method includes the following aspects:
Ensuring backup cutters do not cut or only partially cut when their primary cutters experience little-to-no wear and when the penetration per revolution of the bit does not exceed an expected value. This aspect is enabled by allowing backup cutters to have a minimal critical depth of cut that is greater than the depth of cut of the primary cutters.
Ensuring that backup cutters act as active cutters when the primary cutters’ wear depth is equal to or greater than the underexposure of the backup cutters. This aspect is enabled by allowing each backup cutter to be rotationally behind its primary cutter by approximately 150° or greater. The underexposure of each backup cutter relative to its primary cutter is calculated carefully on the basis of the primary cutter's wear and drilling conditions.