Research On The Flowing Behavior Of Produced Fluid In Polymer Flooding Wells

At present polymer flooding has been used widely as a means to increase the recovery factor of water flooding oilfield. The rheological characteristic of the produced fluid is changed when the polymer solution breaks through the produced wells. According to the content of the polymer solution in produced fluid, the Newtonian produced fluid may be changed to non-Newtonian fluid or viscoelastic fluid, which leads to more serious production problems compared with the water flooding wells, such as eccentric wear of the sucker rod. In order to provide theoretical supports for solving these problems, the flowing behavior of the produced fluid and the mechanism of eccentric wear of the sucker rod in polymer flooding wells would be investigated in this article.The oscillating flow in concentric annular under the periodic gradient and the unsteady flow in the concentric annular with the inner wall moving to and fro axially for the Newtonian fluid and the Maxwell viscoelastic fluid were researched theoretically by the method of eigen function. The oscillating flow due to the velocity pulsation at the annular entrance and the unsteady flow in the concentric annular with the inner wall moving to and fro axially for power-law fluid were studied numerically by the SIMPLE method. The velocity profile, average velocity, the wall stress or the frictional factor of the two flowing cases for the Newtonian fluid, the power fluid and the voscoelastic fluid were obtained. The influence of the annular space, fluid parameters, the pulsating frequency and amplitude on the flowing behavior were discussed. The derivation process and the numerical algorithm were proved to be correct by discuss of some special cases.The mathematical models of the oscillating flow in eccentric annular under the periodic gradient and the unsteady flow in eccentric annular with the inner wall moving to and fro axially for the power-law fluid and the Maxwell fluid were set up and solved numerically by the finite volume method and the finite difference method respectively in the bipolar coordinate system. The velocity profile, the flow rate of the two flowing cases for the two fluids were obtained. The effects of the annular eccentricity, fluid parameters, the pulsating frequency and the amplitude on the flowing behavior were investigated. The analysis for the sucker-rod pumping systems showed that the unstability and flexion of the sucker rod under the combined action of the axial concentrated force at the plunger pump and the axial distributed force along the rod and the lateral force along the rod due to the elasticity of the produced fluid containing polymer in eccentric annular were the reasons of the eccentric wear of the sucker rod in polymer flooding wells. The eccentric wear of the sucker rod under the action of the lateral force was special for the polymer flooding wells. The Maxwell fluid was used to calculate the lateral force in the eccentric annular. The reasons why the eccentric wears of sucker rod in polymer flooding wells were more serious than that in water flooding wells were that the bodiness trait of the polymer solution, which made the neutral point upper shift, increased the bending load and decreased the critical bending load, and the lateral forces, which can exceed the load to cause the eccentric wear of the sucker rod easily as the length of the rods increased. Appropriate measures were put forward based on the mechanisms of eccentric wear.