Screw Drill Vibration And Vibration Analysis

Screw drilling tool is the most widely used downhole motor at present. In the work process, screw drilling directly is subjected to impact loads from the drill bit, the force of string bearing is very bad, and the fluctuating load and violent vibration will not only lead to the inner and outer rings of bearing broken, also accelerated wear on bearing. The string bearing is one of the short life components on the screw drilling, it affects the machine life and greatly shortens the cycle of trip, and it not only prolongs the drilling period also increases the cost of drilling. Therefore, it is of great significance to analyse the vibration of screw drilling tool and take corresponding measures to reduce the vibration of string bearing and prolong the service life of bearing string.This paper simplifies the existing mechanical analysis of screw drilling tool, establishes the mechanics model of screw drilling tool, and also establishes the model of drilling tools below the neutral point in the ADAMS software, then analyse the contact force of four cases and two kind of clearances on bearing. And then put forward three vibration system, establish the mechanical model of each control scheme, and also establish the drilling tool model for each scheme in ADAMS, analyse the effect of three damping schemes. Because the damping effect of scheme three is relatively good, so the finite element model is established based on scheme three, then analyse the stress level of rolling body and inner and outer rings of bearing, the displacement of drill string and the changing law of speed under different excitation frequency in order to further determine the damping effect of scheme three.The simulation results show that, the displacement excitation of the drill bit can cause the screw drilling string bearing generating larger contact force. Between three types of damping schemes put forward in this paper, the damping effect of scheme one is worst, it is subjected to the internal structure of screw drilling tool, the stiffness value of the damper is too large, but excessive stiffness leads to low frequency vibration can not be realized. Comparing with scheme one,the damping effect of scheme two is good, because the damper stiffness value is greatly reduced, so the contact force decreases obviously; In scheme three, the damper is mounted directly upon the bit, it can effectively isolate the excitation from the drill bit, so bearing string is not subjected to direct impact, the stress of each component of string bearing and displacement of the upper drill string are in the lower level.