Numerical Calculation Of Unsteady Flow Of Viscoelastic Fluid In The Eccentric Annulus

The technique of polymer-flooding can increase oil recovery by more than 12% on the basis of water-flooding, and gain enormous economic benefits, meanwhile, come forth a few problems, such as the eccentric wear of the sucker rods aggravates, the period of examining pumps and the life span of the sucker rods shortens, broken rod increases and so on. So, the eccentric wear of the sucker rods has been a problem that needs to be solved quickly. The experiment proves that the elasticity of polymer solution makes the sucker rods get a radial force perpendicular to its axes when the sucker rods of polymer flooding well does periodical in-and-fro motion in the eccentric annulus, and the radial force makes the sucker rods lose stability earlier when it was pressed down stroke, and aggravate eccentric wear of the sucker rods of polymer flooding well. Adopting common conversion Oldroyd-Maxwell constitutive equation, in this paper, the flow equation of the unsteady flow of viscoelastic fluid in the eccentric annulus was established, and was discretized with control volume method; velocity profile of the flow field was obtained by using ADI (Altering Direction Implicit) iterating method; the influence of eccentricity of annulus and motion parameter of the sucker rods on the velocity profile was discussed detailedly; the normal force acting on the sucker rods and the radial force acting on the inner rods were calculated, geometry parameter of flow field, fluid elasticity and the motion of the sucker rods that have influence on the normal force were analysed. The result shows that eccentricity and motion velocity of the inner rods have the most important influence on the flow field; eccentricity and fluid elasticity are the ultimate causes of radial force, With eccentricity increases, both flow rate and radial force also increase, when motion velocity of the inner rods increases, the peak value of flow rate and radial force increase, too; the existence of radial force is the ultimate cause of eccentric wear of the sucker rods aggravating in the polymer flooding well; preventing eccentric wear should start with reducing eccentricity. According to the above theory, measures of centralizing the sucker rods in whole bore to prevent eccentric wear have been applied to more than 6000 ploymer-flooding wells in the Daqing Oil Field, and bring about increased economic benefits.