Numerical Calculation Of Force Acting On The Inner Cylinder By Viscoelastic Fluid While The Cylinder Moving Axially In Eccentric Annulus

As one of the major EOR methods, polymer flooding is widely used and does wellin Daqing Oilfield, but there also exist a lot of problems in the rod-pumping wells ofpolymer flooding compared with water flooding, such as lower pumping efficiency,eccentric wear and break-off of the sucker rod, shorter cycle of pump checking, etc. Infact, these problems are greatly related with the viscoelastic property of the producedfluid, and the sucker rod is often working in a condition of eccentric in the tube, whicheven aggravates the problems mentioned above. The force acting on the inner cylinderby viscoelastic fluid while exerting an axial motion is studied and numericallycalculated in this paper, and the results are of practical engineering significance foranalyzing the mechanism of sucker-rod wear.The second order fluid with variable coefficients is used to describe the rheologicalproperty of the produced fluid in a polymer flooding well. The basic equations of theunsteady flow of second-order fluid with variable coefficients in the eccentric annuluswith inner cylinder reciprocating axially are established in bipolar system, and thesparse system of the linear equations is numerically solved. The formula of resultantforce acting on the inner cylinder moving axially in eccentric annulus by theviscoelastic fluid is given, and the force is numerically calculated. Moreover, theinfluences of the eccentricity, stroke and frequency of the inner cylinder on themagnitude and direction of the resultant force are analyzed.The force acting on the inner cylinder by the viscoelastic fluid while the innercylinder moving axially at a uniform velocity in the eccentric annulus is carried out inthe paper. As to second-order fluid, the numerical results show that T_x makes the innercylinder eccentric while the cylinder stays stable, where T_x is the resultant force actingon the inner cylinder in x -direction;and maks the inner cylinder concentric if thepressure gradient is small while the cylinder is exerted a upward or downward velocity,and vice versa;and the effects will be even obvious if the eccentricity being increased;but as to power-law fluid T_x will be zero. The force resultant force T_z acting on theinner cylinder is much smaller than T_x whatever it is considered as second-order orpower-law fluid.The force acting on the inner cylinder by the viscoelastic fluid while the innercylinder reciprocating axially in the eccentric annulus is carried out in the paper either.As to second order fluid and the given pressure gradient, the numerical results show thatthe resultant force Tx acting on the inner cylinder makes it concentric in the upwardstroke, and makes it eccentric in the downward stroke;but the force will make iteccentric no matter in the upward or downward stroke when the pressure gradient ishigh enough and as to power-law fluid the force Tx is zero. As to second-order fluid, theforce Tz acting on the inner cylinder is impetus during the accelerating period andresistance during the decelerating period, and has the same magnitude with Tx;but Tz isso small that can even be ignored when the constitutive equation of power-law fluid isused.