RELATIONSHIP BETWEEN THE AXIS CRITICAL FORCE AND THE SPEED OF THE DRILL STRING WITH HELICAL BUCKLING

The usually applied buckling criterion of drill sting is Lubinski’s axis critical force when investigating the buckling of drill sting in deep straight well.However,this criterion is obtained in studying the buckling of drill sting at static state.In engineering,the dill sting will affected by a lot factors.As a result,there are defects in this criterion.Consequently,this paper investigates the relationship between the axis critical force under helical buckling and the maximum speed of drill string.According to the energy method,we first consider that the helical buckling energy of drill string equals the work of the eccentric force plus the work of the gravity and then obtain a mathematics model for the speed and axis critical force.Considering the inertial eccentric force and the weight of the drill string,we find that the axis critical force will be obviously less than that under the static state,which makes up for the Lubinski’s axis critical force criterion and should be very important in drill engineering applications.