The effects of downhole vibrations on the performance of poly-crystalline diamond compact (PDC) bits have been well discussed in recent years. However, most studies on the downhole dynamics of roller-cone bits have focused on axial vibration and its effects. The questions that remain to be answered are what kinds of vibrations a roller-cone bit experiences and what the effects of these vibrations are on roller-cone bit performance.

To investigate these questions, a series of laboratory and field tests was conducted. Downhole vibration data were recorded by an advanced instrumented sub. Soft-to medium-hard formations were drilled with four 8½-in. roller-cone bits (IADC 517). Three kinds of harmful vibrations were observed, and their effects on bit performance in terms of rate of penetration, insert breakage, and bearing/seal life are discussed.

You can access this article if you purchase or spend a download.