Modeling and experimental investigations on the drag reduction performance of an axial oscillation tool

The high friction of a drill string against a wellbore is a concern during directional and horizontal drilling. An axial oscillation tool (AOT) is typically used to reduce drag and torque. This study examined the axial oscillation drag reduction mechanism using a specially designed laboratory test rig. An indoor simulation experiment was conducted, followed by model recognition and identification of the friction model parameters based on the experimental data. A torque/drag model and drilling string axial vibration model were used to establish the numerical model. Additionally, the boundary condition between the drill pipe and wellbore was based on a nonlinear dynamic friction model. Finally, the model was solved using a numerical method to gain an understanding of the drag reduction mechanism of the axial oscillation tool. The indoor experiment of the nonlinear friction model revealed that the Coulomb friction model appeared to disagree with the measured data of the experiment. The nonlinear dynamic friction model, however, which was based on the acquired parameters using particle swarm optimization (PSO), yielded results that were in good agreement with the experimental results. Comparisons with experimental setups, data and models from the literature were conducted. The simulation results clearly demonstrated that the friction reduction was effective when the amplitudes of the vibration velocities exceeded the drive velocity. Decreasing the slip velocity of drill strings and increasing the amplitude of the axial oscillation tool vibration force effectively lengthened the drilling-string vibration range. Furthermore, the optimal position of the axial oscillation tool corresponded to a highly deviated well section that was characterized by the existence of high friction resistance. Therefore, the oscillation motion of the drill pipe at a highly deviated well section could significantly decrease the total friction force of the entire drill string.