Study on the influence law of stiffness and damping of shock absorber based on drill string vibration

Abstract

With the increasing number of deep wells, ultra-deep wells and ultra-deep wells, the problem of drill string vibra-tion damage is becoming more and more obvious. Shock absorbers are commonly used to reduce vibration. However, the existing research has not fully revealed the influence of shock absorber stiffness and damping on the vibration characteristics of drill string, and the factors considered in the whole well drill string dynamics model are usually limited. Therefore, based on the Hamilton principle, this paper establishes a dynamic model of the whole well drill string with shock absorbers considering the actual drilling wellbore trajectory, drilling fluid vis-cous damping and random contact collision between the drill string and the wellbore wall, and studies the vibra-tion characteristics of the whole well drill string for the stiffness and damping of the three shock absorbers. The results show that the stiffness of disc spring damper is better at 3.5kN/mm or 5kN/mm, and the vibration of drill string decreases by 14.6% ∼ 14.8% compared with that without damper. The hydraulic drill string damper has a good vibration reduction effect in the range of 120 ∼ 200 N·s/mm, and the vibration reduction is reduced by 26.9% ∼ 28.0%; the torsional damper has a vibration reduction effect on the drill string in the range of 10 ∼ 200N·s/mm damping value, but the vibration reduction effect is relatively better in the range of 120 ∼ 160N·s/mm, and the vi-bration is reduced by 11.7% ∼ 14.6%. The research results of this paper provide theoretical support for the design and selection of shock absorber stiffness and damping.