Study on dynamic buckling characteristics of drill string in horizontal well based on stochastic model

The buckling of drill string will increase the difficulty of running casing and accelerate the damage of drill string. Many achievements have been made in the study of drill string buckling, but few studies consider the influence of randomness on it. Due to the irregularity of the horizontal wellbore, the contact collision and friction between drill string and wellbore are random. The simplified analysis model of drill string buckling, the probability distribution of radial clearance between drill string and wellbore and the stochastic model describing friction coefficient are established. Through numerical solution, axial displacement, angular displacement and contact force of drill string unit under the action of random parameters are obtained. Four kinds of response results are obtained by repeated simulation calculations of the buckling model, and the probability of occurrence is 75%, 5%, 5% and 15% respectively. Concerning the outcome with the highest probability (75%) of occurrence, parametric randomness has the least effect. The drill string used in this case should have a large torsional stiffness. Concerning the outcome with the lowest probability (5%) of occurrence, parametric randomness has the greatest effect. Therefore, the strength and stiffness of drill string used should be large enough. At the same time, in order to change the contact state and friction between drill string and wellbore, it is necessary to use anti-friction tools. What's more, the randomness of the parameters mainly affects the response results when drill string is buckling. After stabilization, axial displacement is almost unaffected, there is a 5% probability that contact force will be affected. Upper drill string has greater buckling degree, so the influence of parameter randomness is greater. Considering the influence of the randomness of the parameters on the buckling, more comprehensive stability evaluation results can be obtained, and it is also helpful for the risk assessment of drill string stability.