Numerical Calculation Of Flow Rate Of Swabbed Fluid Flowing In Wellbore Under Polymer-flooding Operating Mode

As one of the major EOR methods, polymer-flooding is widely applied and has been proved to be effective in Daqing Oilfield, but there also exists many problems about the polymer-flooding rod-pumped wells compared with water-flooding ones, such as lower pumping efficiency, sucker-rod wear and sucker-rod break-off, shortened pump inspection cycle, etc. During oil production, pumping rod is eccentric in the long oil tube, in which flow of the swabbed fluid can be regarded as an unsteady flow of second-order fluid in eccentric annulus with the inner cylinder reciprocating axially. Therefore, under the condition of polymer-flooding, researches on flow rate of the produced fluid flowing in the eccentric annulus between sucker-rod and tube are of practical significance to optimize operational parameters of polymer-flooding rod-pumped wells.In this paper, the second order fluid was used to describe the viscoelastic rheological property of the swabbed fluid in a polymer-flooding well. The motion equation, initial condition and boundary conditions of the unsteady flow of second-order fluid in the eccentric annulus with inner cylinder reciprocating axially were introduced under bipolar coordinate system, and the expressions of instantaneous flow rate and average flow rate of the flow were introduced as well. Using HPAM aqueous solutions, the motion equation was numerically solved by finite volume method. Instantaneous flow rate and average flow rate were also numerically calculated. The influences of stroke and frequency of inner cylinder and the influence of eccentricity of annulus on instantaneous flow rate distribution and average flow rate were analyzed. Instantaneous flow rate distribution and average flow rate of unsteady flow of HPAM aqueous solutions which can be regarded as second order fluid in eccentric annulus with inner cylinder reciprocating axially were compared with those of HPAM aqueous solutions which can be regarded as power law fluid. The average flow rate numerically calculated by finite volume method was compared with that by finite difference method.The numerical calculation results show that, stroke and frequency of inner cylinder and eccentricity of annulus have obivious influence on instantaneous flow rate distribution; stroke and frequency of inner cylinder hardly effects average flow rate, but eccentricity of annulus has obvious influence on it; the differences of instantaneous flow rate distribution and average flow distribution of HPAM aqueous solutions which can be regarded as second order fluid and power law fluid, respectively, are very obvious, which indicates the influence of elasticity on flow rate is obvious as well; the average flow rate numerically calculated by finite volume method accords well with that by finite difference method, which indicats that it is correct to numerically solve the motion equation by finite volume method used in this paper.