Abstract
The reversal and lateral vibration of the drill string are very complex motion and can affect the normal operation of the drill string. The movement of the drill string in the stepped well is different from the movement of the drill string in the regular well. The vibration of the drill string in the stepped well varies with the size of the wellbore and can be visually reflected by the phase speed. To find out the relationship between reversal and lateral vibration, the natural frequency of lateral vibration of the drill string was solved by using the method of energy conservation. The analysis shows that the phase speed of flexural wave in the stepped well is faster in small size wellbore than in large size wellbore. The reversal and lateral resonance is easy to happen in small size wellbore, and the reversal will excite lateral vibration. When the sum of reversal and rotational angular frequencies approaches the natural angular frequency of lateral vibration, the lateral resonance will occur.
Highlights
In the process of petroleum drilling, drill string system plays an important role
At 120 meters of stepped well, the upper joint of a drill string is in the large size wellbore and the lower joint is in the small size wellbore
2) From the phase speed, it can be seen that the phase speed of well sections with small annulus rate is small, and the phase speed of well sections with large annulus rate is large
Summary
In the process of petroleum drilling, drill string system plays an important role. Appropriate vibration of the drill string is beneficial to clear the bottom cuttings, to improve the rock-breaking efficiency and reduce the sliding friction [1,2,3,4,5]. Han [10] studied the nature frequency of lateral vibration of the drill string. She concluded that the nature frequency of lateral vibration of the drill string was related to the nature of itself and the axial force exerted. Han and Yan [14] established the lateral vibration equation of drill string in the presence of axial load, and the nature frequency of lateral vibration of the drill string was obtained, and concluded that the reversal of the drill string was an important factor to stimulate the lateral vibration. The application of stepped wells in practice is very important, but no scholars currently have studied the drill string reversal and lateral vibration in stepped wells. By the example analysis of the failures of the drill string, the relationship between the reversal and lateral vibration in the stepped well was found out
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