Feasibility study on roller-cone bit wear detection from axial bit vibration

Previous studies reported that the peaks of a power spectrum for roller-cone bit axial vibration move to higher frequencies with the progression of bit-tooth wear. This result implies that monitoring and analyzing roller-cone bit vibration could be a new real-time detection method for downhole bit wear conditions.In this study, the dynamics of roller-cone bit axial vibration were modeled to quantitatively evaluate bit-tooth wear. The model includes the kinematics of roller-cone bit motion and a model for bit-tooth/rock interaction that considers the detailed geometry of a worn tooth. By sequentially solving the equation of motion with increments of cone rotation angles, the time history of axial bit vibration was simulated.The developed model was validated by comparing the power spectral densities for the simulated time histories of axial bit vibration with the experimental results of full-scale drilling tests. Detection of bit-tooth wear, bearing failure, and broken teeth was studied from a feasibility perspective.

► We modeled the dynamics of roller-cone bit axial vibration.
► The model considers the kinematics for the detailed geometry of a worn tooth.
► The model can simulate the power spectra of axial bit vibration.
► We simulated the vibration power spectra for various bit wear states.
► Tooth wear and lost cones could be detected by the monitoring of the power spectra.