An Efficient Simulation Method for Deep-Vertical-Well Drillstring Dynamics Based on Nonlinear Beam Element

Summary In the research field of drillstring mechanics, there are two main problems: First, the upper boundary conditions of the lower drillstring model are not accurate enough, and second, the computational efficiency of the full-well drillstring model is low. To address these problems, a solution based on a kind of free flexible beam theory (geometrically accurate beam theory) is proposed in this paper. By converting the key parameters of the upper drillstrings, such as mass, friction, and stiffness, into equivalent ones, we establish a dynamically equivalent and efficient drillstrings model. Compared with the full-well drillstring simulation method, we find that the efficient drillstring model achieves a significant reduction in computation time, specifically from 80.53% to 93.24%. Furthermore, we compared the efficient drillstring model coupled with the dynamic loads of rock breaking with the results of indoor tests and full-well drillstring. The comparison results show that the errors between the computational results of the efficient drillstring model and the indoor test results range from 0.405% to 11.11%. In addition, we also found that the efficient drillstring model is consistent with the experimental results in terms of the parameter influence pattern, which further verifies the accuracy of the efficient drillstring model. The efficient drillstring model can simulate the actual rate of penetration (ROP) and torque on bit (TOB) with an error of less than 10% for different depths in the field, which indicates that the model is also highly accurate in practical applications. This paper’s research has significant academic value and practical application relevance as it not only offers theoretical support for the optimization of the mechanical model of drillstrings but also offers helpful direction for experimental research and field application.