Contact interaction between bottom drillstring and borehole wall and its effect on drillstring failure

During drilling, the collision-friction interaction between the bottom drillstring and the borehole wall is extremely intense, which will exert effect on the lateral movement of drillstring and result in bottom drillstring failure or make it worse. Based on using a status analyzing model of the bottom drillstring, the mechanism and law of the effect on bottom drillstring failure due to the contact interaction is simulated and analyzed. It is shown that the contact interaction enables bottom drillstring to whirl backward, and then an alternate bending stress with higher frequency is produced. So the drillstring fatigue failure could be accelerated. At the same time, a quite strong wallop force of high frequency is produced on the contacting point, and the contacting zone is next to the screw coupling of drill collars. It will easily result in the failure of screw couplings. The research results provide theoretical basis for the prevention of drillstring failure.