Buckling and dynamic analysis of drill string system in horizontal wells

Compared with vertical wells and deviated vertical wells, the dynamic characteristics of the drill string in horizontal wells are more complicated and more prone to failure because of the drag-pressure effect under gravity. Most researchers only consider the movement of some drill strings at a certain depth and do not analyze the rotary drilling process of the whole drill string. When most researchers do drill string simulation research, the drill string system diameter of the simulation model is consistent, and the actual drill string assembly is not considered. Based on the finite element method (FEM) and the nonlinear dynamic equation of drill string, the drilling simulation model of the drilling string system in a horizontal well is established by considering the curved hole trajectory and the nonlinear impact contact between the drill string and wellbore. The buckling and dynamic characteristics of the drill string in horizontal wells are analyzed by simulating the whole drilling process, the effect of rotating speed and hook load on the buckling characteristics of the drill string, and the effect of hook load on the whole dynamic characteristics of drill string system are analyzed. The results show that in the drilling process, the buckling deformation of the drill string near the wellhead presents a trend of"Sinusoidal buckling-helical buckling-sinusoidal buckling," the "sinusoidal buckling-helical buckling "appears near the oblique section. When the hook load applied at the end of the drill string is greater than the critical value, the drill string will get stuck during drilling. When it is less than the critical value, the greater the value of the hook load, the more stable the axial feed and lateral vibration of the drill string, and the smaller the contact force between the drill string and the wellbore. With the increase in rotating speed, the vibration period of the drill string decreases, and the amplitude of the vibration increases. With the increase of drill string drilling depth, the buckling deformation of the drill string can be reduced by reducing the value of the hook load. The conclusion is that the research results can be helpful for drill string design and structural optimization.