Experimental Evaluations of Drill Bit and Drill String Dynamics

Abstract

Abstract Laboratory and field experiments were performed to investigate the dynamics of the drill bit and drill string. Laboratory results for Anti-whirl and conventional polycrystalline diamond compact (PDC) bits showed that vibrations of the former were an order of magnitude less than those of the latter. Backward whirl of the conventional PDC bit was prevalent in both hard and soft formations. Roller cone bit tests suggested that they too were subject to backward whirl, and the lateral vibrations that resulted were an order of magnitude worse than the axial vibrations commonly associated with these bits. Field tests were performed using a single drill string design with the conventional PDC and roller cone bit. Simultaneous surface and downhole measurements were made. Results suggested that bit vibration amplitudes rapidly diminished with distance from the bit, and that stabilizers had a significant isolating effect. Surface measurements were found to be inconclusive with respect to downhole behavior. In some instances correlations could be drawn between surface accelerations and those downhole; in others surface vibrations were severe, while little was measured downhole; in still others downhole vibrations were dramatic, while nothing was indicated at the surface. Operational recommendations are made based on experimental observations.