A feasible model for friction-reduction investigation of drillstrings in long-horizontal wells with axial oscillation tools and analysis of key influencing factors

Abstract

Most researchers focused on investigating of the friction-reduction effect of the working parameters of the axial oscillation tool (AOT), and didn't pay sufficient attention to the influences of drillstring material properties and wellbore parameters. In this paper, a FEA model was established by considering the coupling of the drillstring-wellbore contact and the action of AOT. The “far end” boundary condition and a dynamic boundary condition are introduced into the FEA model, which was verified analytically and experimentally. Finally, the effect of AOT parameters (excitation force, excitation frequency and location), drillstring material properties and wellbore parameters (inclination angle, friction coefficient) on the friction-reduction and the drillstring vibration are systematically explored. The results show that the friction-reduction is mainly influenced by AOT parameters, drillstring material properties and friction coefficient, and is slightly influenced by the inclination angle. Based on the analysis, the friction-reduction of the AOT is mainly caused by the change of friction direction. Though less than the effect of friction-direction change, the effect of velocity-based friction coefficient should not be ignored.