Mechanical behavior of drillstring with drag reduction oscillators and its effects on sliding drilling limits

作     者：Xiao-Lei Shi Wen-Jun Huang De-Li Gao Xiao-Lei Shi;Wen-Jun Huang;De-Li Gao

作者机构：MOE Key Laboratory of Petroleum EngineeringChina University of PetroleumBeijing102249China 

出 版 物：《Petroleum Science》 (石油科学（英文版）)

年 卷 期：2021年第18卷第6期

页      面：1689-1697页

核心收录：

学科分类：0820[工学-石油与天然气工程] 082001[工学-油气井工程] 08[工学] 

基　　金：financial support from the Natural Science Foundation of China (Grant Nos. 51904317, 51821092, U1762214) Science Foundation of China University of Petroleum, Beijing (Grant No. ZX20180414)。 

主　　题：Drillstring Downhole oscillator Friction force Drag reduction Sliding drilling 

摘      要：Practice has proved that drag reduction oscillators can decrease the axial friction and increase wellbore extension effectively in sliding drilling operations.However,the complicated mechanical behavior of drillstring with drag reduction oscillators has not been revealed sufficiently.In this paper,the mechanical model of drillstring with drag reduction oscillators is established by considering the friction nonlinearity.Further introducing the initial conditions,boundary conditions and continuity conditions,the finite differential equation of drillstring vibration is obtained and solved.The new model has been applied to a case study,in which the drag reduction effects of drillstring with and without oscillators are compared and the effects of relevant factors on drag reduction are analyzed.The results show that the hook loads increase obviously by reducing downhole average friction coefficient for drillstring with oscillators.Increasing vibration amplitude of the drag reduction oscillator can decrease axial friction,but the vibration frequency is nearly irrelevant to drag reduction.Increasing number of drag reduction oscillators can decrease axial friction,but may lead to large hydraulic power loss and high risk of drillstring fatigue.Therefore,there is an optimal number of drag reduction oscillators.The re search re sults are of significant guiding significance for optimal design and safety control in sliding drilling operations.