The Research & Analysis Of The Drill String's Lateral Vibration In Ultra-Deep Well

The vibration of drill string in practical engineering is inevitable. The vibration includes three types, while the lateral vibration is an important one. The strong wave of drill string which is caused by lateral vibration can lead to severe failure of drilling. It will put more difficulty and risk on drilling, even bring huge loss in economic.Theoretical analyses of the lateral vibration in ultra-deep well are discussed in this article. The cause of lateral vibration, mechanical discipline and affecting factors are concluded to establish mechanical model and equations for calculating the vibration frequency. As the equations for calculating vibration frequency is concord function, which is very difficult to be solved. So this dissertation will use ANSYS to simulate and analysis the drill string's lateral vibration. The mechanical model is built by ANSYS which is based on APDL Language. The drill string assembly of ultra-deep well which is as long as 10000 meters are also designed.Assuming the drill hole is vertical, taking no account of connectors and bit geometry. By studying the natural frequency and natural vibration mode, we can get the influence of temperature and axial force. The result shows: when the axial force is compressive force, the natural frequency of lateral vibration will decrease; when the axial force is tensile force, the natural frequency will increase. The natural frequency will go down as the temperature increase. Once the temperature goes up to 300 degrees, the natural frequency of lateral vibration will drop significantly. All in all, the range of resonance frequency is very wide.This paper provides theoretical basis for us to research the resonant of drill strings, strength failure and the position of centralizer, it has a reference meaning to the drill string's design, manufacture and engineering application.