Dynamic Analysis Reveals Stability of Roller Cone Rock Bits

Abstract

ABSTRACT The cutting structures of roller cone bits often experience catastrophic failures resulting from dynamic load variations beyond the capacity of the cutting elements. Continuous improvements to cutting structures have steadily increased penetration rates, but at the same time have elevated their sensitivity to these dynamic effects. Until recently, the causes of these failures were difficult to identify. This paper details a series of roller cone bit tests that discovered a new explanation for cutting structure failure. In the tests, roller cone bits drilled Carthage marble under atmospheric pressure and the system response was monitored. Measurements were taken of new and dull bits, some of which incorporated unconventional cutting structures. Lateral movements of the bit included directional reversals and orbits about the hole center. Certain motions were identified that may result in cutting structure breakage. Included in the paper are examples from kinematic models that capture the essence of the motion and reveal its harmful effects.