Characteristics Analysis Of Multi-dimensional Fluid-structure Interactional Vibration In Completion String

In the process of well testing and completion,due to many factors,the fluid in the string is usually in an unsteady flow state,which will induce the interactional vibration between the string and the fluid.Strong vibration will cause fatigue damage to the string and accessories,especially at the connection position,not only affects the connection strength and tightness of the joint,but also aggravates the stress concentration at special structure and increases the stress on string itself.When the stress beyond the bearing capacity of the string,it may lead to string damage and leakage,packer loss and other problems,and even cause explosion,combustion and other safety accidents.In this paper,based on the Timoshenko beam model,considering the effects of fluid viscosity and gravity,the quasi-linear 14-equation model of fluid-structure interactional vibration of the completion string is established.In this model,Poisson coupling and friction coupling are considered.Aiming to completion string,several optimizations have been made.Compared with some simplified models,this model is theoretically more suitable for completion strings.In the solving process,the finite difference method is used to discretize the characteristic equations,which are got by the characteristic line method.The time interpolation method and the space interpolation method in the paper are used to obtain the form of the parameters that can be used for iterative calculation.According to the model,for the fracturing conditions,the vibration parameters of the string and fluid at the time of pump starting and stopping are calculated.Based on the results,the impact of some factors on the vibration are analyzed,and it gives some suggestions and measures to improve the string safety.