Modeling friction-reducing performance of an axial oscillation tool using dynamic friction model

• A model for analyzing the friction reducing performance of AOT is proposed.
• Dahl model can accurately explain the mechanism of friction reducing of AOT.
• The friction reducing is a consequence of cyclic changes in the sign of FF→.
• The friction reducing concerns with the elastic deflection of asperities.
• The amplitude of AOT should be systematically optimized during the process.

An axial oscillation tool (AOT) is an effective means to solve the problem of high friction observed in structurally complex wells during sliding drilling. However, the classical Coulomb model does not explain the mechanism of friction reduction caused by the AOT. To solve this problem, a theoretical model for the analysis of frictional force is proposed based on the dynamic friction model and microscopic contact deformation theory. The Dahl model, an innovative dynamic friction model, is used in this model to determine the friction force changes during slide drilling with an imposed axial vibration. A computational program is developed in the Matlab/Simulink environment. The results indicate that the calculation results using the present model and the experimental results are in good agreement (the average error is only 5.09%), verifying the accuracy of the present model and method. The reduction of friction increases with the vibration frequency and tangential contact stiffness coefficient; it first increases with vibration amplitude and then tends to decrease before reaching the optimal amplitude, but it decreases with increasing relative sliding velocity. The instantaneous frictional force does not exhibit an abrupt phenomenon. The prerequisites for reducing friction caused by the AOT are that the relative sliding velocity should be less than the maximum velocity of the axial vibration. The present model can quantitatively characterize the axial vibration and the relationship between the frictional force and asperity deformation during sliding drilling, and it also can be utilized to analyze the variations of frictional force in real-time. In addition, this model can provide a quantitative calculation to predict the frictional resistance in horizontal drilling.