Numerical Analysis Of Coupling Vibration And Collision Characteristics Between Slender Rotating Rod String And Produced Fluid

In the process of oil exploitation,the motion state of the slender rod in the tubing is axial reciprocating motion and rotating motion.The force of the produced liquid in the annulus on the rod changes along the depth of the well,which causes the rod to jump off and collide with the inner wall of the tubing.Meanwhile,the motion state of the rod also affects the flow state of the produced liquid.This is a typical fluid-structure coupling vibration problem between annual.In this paper,based on overset mesh and domain solving algorithm,a mechanical model of rotating rod immersed in fluid in wellbore was established.Considering the complex dynamic boundary caused by the collision between the rotating rod and the tubing,the fluid domain in the rod was discretized into hexahedral mesh,and the annulus fluid domain was discretized into mutually overset background mesh and component mesh.Intergrid boundary condition information interpolation formulas of two sets of mesh were derived by using secondorder precision interpolation method,and the whole fluid domain was described by computational fluid dynamics equations.The solid domain of the rod was discretized into threedimensional solid grid and described by structural dynamics equation.According to the geometric coordination and load balance conditions of the fluid-structure coupling interface,the physical variable transfer formula and the normalized convergence criterion of the coupling interface were derived,and the domain coupling algorithm was established,so as to form the numerical calculation method of coupling vibration and collision between the slender rod and the produced fluid.The above method was used to calculate the ultimate drop of spherule and the positive and oblique collision between spherule and wall in static fluid.The displacement,velocity,incidence angle and reflection angle of spherule in the collision process were in good agreement,which verified the correctness of the numerical calculation method in this paper for the solidto-solid collision simulation in fluid domain.The collision characteristics of rod and wellbore under different fluid viscosity and rotation velocity in plane were also studied.The results showed that the collision force between rod and wellbore decreased with the increase of viscosity,and the movement range of rod was negatively correlated with fluid viscosity.With the increase of rod rotation speed,the collision force between rod and wallbore increased,and the movement range of rod was positively correlated with its rotation speed.When the rod collided with the wellbore,the velocity of each point on the rod changed abruptly.According to the actual working state of the rod,a simulation experimental device of the vertical rotating rod and the internal and external fluid coupling system was designed and built.The numerical results were compared with the displacement results of the experimental measuring points,and the two results were in good agreement.Based on the method established in this paper,the coupling vibration and collision characteristics of the slender rotating rod and produced fluid under different fluid viscosity and rotation velocity were studied.The results showed that the larger the fluid viscosity was,the more obvious the influence of viscous resistance of fluid on the motion of rod was,the smaller the contact pressure was and the smaller the vibration was.The larger the rotational speed of the rod was,the more intense the vibration was,the more obvious the influence of torsional deformation on the motion of rod was,the smaller the normal acceleration during the collision was,and the smaller the contact pressure was.When the collision occured between the strings,the acceleration of each point of the rod changed abruptly and the vibration intensified.The calculation results in this paper can provide a theoretical basis for reducing rod vibration,eccentric wear and detachment.