STUDY ON NONLINEAR DYNAMICS AND BIFURCATIONS IN ROTATING COMPRESSIVE-DRILL STRING

In drilling process of horizontal wells, the transverse vibration of drill string likely occur due to axial compression, which may cause serious accidents such as drill string failure and hole expanding etc. In this paper, the compressive-drill string is simplified as a revolving flexible beam subjected to a load condition simplified from complicated excitations of drill string. Thus, the nonlinear dynamic model of flexible drill string is established based on the von Karman theory, where the partial differential equation is discreted by Galerkin method, and then the nonlinear control equation of drill string is acquired, and the average equation is obtained by multiscale method. The complex behaviour of flexible drilling string in resonance is analyzed by nonlinear dynamic method, and the dependence of nonlinear dynamics responses on rotating speed is investigated. The research results will provide a theoretical basis for the practical efforts of decreasing failure rate, improving drilling rate and reducing drilling cost during the drilling process of horizontal well.