Some peculiarities of the drilling rigs elements movement

Abstract

This paper deals with investigatson of the process of drill bit whirling on the rough plane of the well bottom. Nonholonomic kinematic models of the mechanical interaction of contacting bodies with defects at the initial stage of system self-excitation are applied. On the basis of the results of experimental studies, it is believed that one of the main factors influencing on the whirlings vibrations is the geometry of the bit. The bit is considered to be an absolutely rigid ellipsoidal body, the well bottom surface is supposed to be a plane. The resulting oscillations are associated with spontaneous bending deformations of the drill string, which are accompanied by continuous contact of the bit and the rock. The equations of motion of the bit in the linear approximation are obtained. The analysis of the solution of the linearized equations is carried out, and the frequencies of the arising periodic motions are found. The forms of oscillations under different geometrical parameters of an ellipsoidal bit are analyzed. It is shown that the bit can rotate in backward direction, moving at angular velocities that exceed the angular frequency of the drill string. The research results can be used in the development of new types of drilling rigs.