Research on how the form of vibration affects the efficiency of the axial oscillation tool.

Abstract

This study assesses the performance of drill string axial oscillation tool utilizing different excitation force waveforms. A numerical investigation was conducted using a simulation model of the drill string developed in Modelica. The model represents a composite beam with distributed parameters along its length, equipped with an axial oscillation tool, and positioned in an inclined wellbore filled with drilling fluid.

The simulation employs the soft-string model to represent the drill string dynamics. Viscous interaction between the drill string and the drilling fluid is accounted for, while contact with the wellbore wall is described using the Stribeck friction model. Six waveform types were investigated: harmonic, triangular, trapezoidal, the sum of two synchronous harmonic components, and modified triangular and trapezoidal shapes. These waveforms correspond to typical operational characteristics of existing axial oscillation tool or, based on reviewed literature, are expected to enhance friction reduction and can be generated using available technology.

All cases were simulated using the same excitation frequency. The amplitude of each waveform was selected to yield an identical root mean square (RMS) value, ensuring equivalent energy input for vibration generation.

Simulation results for a drill string section located in an inclined wellbore with an azimuth angle of 39° indicate that trapezoidal excitation provides the most favorable performance. Overall, the comparative analysis shows that axial oscillation tool efficiency increases with the RMS value of the normalized waveform function. Consequently, flatter (less peaked) and more energy-dense waveforms are the most effective for improving axial load transmission and overcoming friction.