Experimental study on the rotation of compression-buckling rod column in a liquid-filled cylinder

Abstract

In oil drilling, the main form of movement of the bottom hole assembly is self-rotation and whirling after buckling. The rotation of a compression-buckling rotation drill string can increase the frictional force between the drill string and borehole wall, induce lateral vibration and whirl of the drill string, generate borehole wall instability and drill string damage, and even cause a drilling failure. At present, studies on the motion laws of a pressure-rotating buckling drill string are incomplete, and some are even incorrect, necessitating further improvements. In this work, the effects of axial load, rotational speed, drilling fluid, and inner diameter on the rotational motion of a compression-buckling column in a cylinder were experimentally studied. The dissipation energy before and after the transition state of the simulated drill string, from the forward whirl to self-rotation, or from the forward whirl to the backward whirl, were analysed. The results indicate the following: (1) With an increase in the axial load, a buckling drill string first experiences forward whirl. Next, both forward whirl and self-rotation occur, along with a combination of backward whirl and self-rotation along the partial vertical wall. Finally, backward whirl occurs along the wall. (2) A dynamic lubrication of the drilling fluid can reduce the forward whirl rotation amplitude of the drill string and prevent the formation of backward whirl. (3) When dynamic lubrication by the drilling fluid is improved, the borehole diameter is reduced, the hole-deviation angle increases, the critical axial load of the backward whirl increases. (4) Backward whirl may occur twice for the drill string as the axial load increases. (5) The state transition of the drill string motion conforms to the minimum dissipation power principle. The experimental results described herein can serve as a reference for studies regarding drill string dynamics and drilling practice.