Reaserch On Rheological Behavior Of Ultrahigh Molecular Weight HPAM Solutions And Flow Field Stirred By Double Helical Ribbon And Screw Impeller

With the widespread application of partial hydrolyzed polyacrylamide (HPAM) solution with ultrahigh molecular weight in the tertiary recovery technology in China, the maturation unit, one process in the preparation of polymer flooding, has become the critical step in the regular operations of oil recovery engineering, which lead to the rheological behavior of HPAM solutions, mixing performance of the stirring apparatus, as well as the HPAM solution flow field in maturation tank need to be further studied.In order to understanding the microscopic properties of HPAM, the hydromechanical radius distribution of HPAM molecular were measured by using Brookhaven laser scattering apparatus. It is found that the higher the molecular weight of HPAM is, the lager the average hydromechanical radius is. Overall investigations on the rheological behavior of HPAM solutions with different concentrations and molecular weights were conducted by means of HAAKE Rheostress 150 rheometer under the scan modes of steady shear flow and dynamic oscillation shear flow. It is shown that, the polymer solutions have significant elastic energy and the apparent viscosity exhibit shear thinning behavior. At the same molecular weight, the apparent viscosity, first normal stress difference, elastic modulus and viscous modulus increase with increasing polymer solution concentration.According to the rheological characteristics of HPAM solutions obtained from experiments, the KBKZ constitutive model was achieved to describe the viscoelastic properties of the polymer solutions, In the process of determining model parameters, a novel method, which can solve all the model parameters using one step by minimizing a established objective function with the principle of nonlinear programming method, was proposed. Through proper simplification, the relaxation time spectrums in the KBKZ equation were reduced.To comprehensively investigate the mixing performance of double helical ribbon and screw impeller, which is suitable for mixing polymer solutions, three dimensional numerical simulation for Newtonian, non-Newtonian fluid, gas-liquid and solid-liquid two phase flow fields generated by this impeller were conducted by using multiple reference frames impeller method. The results show that, the double helical ribbon and screw impeller makes fluid in stirred tank form large axial circulation. The more significant shear thinning properties the fluid have, the lower normalized axial velocity and circulation number in the flow field. The double helical ribbon and screw impeller plays a role to converge and discharge gas for the gas-liquid flow in the stirred tank. However, when the impeller agitates the solid-liquid fluid flow, it is easy to form retention in the central and circumferential region on the bottom of stirred tank. In this case, a combined double helical ribbon screw and anchor agitator has been developed to improve the mixing effect .The HPAM solution flow field stirred by double helical ribbon and screw impeller in stirred tank were measured by particle image velocimeter (PIV), it is found that, there is a great axial circulation in the viscoelastic fluid flow field. Because of the elastic properties of the HPAM solutions, the average velocity and average shear rate in the flow field, to some extent, have been declined.The results of the present work give practical and theoretical values for the polymer solution preparation above ground in enhanced oil recovery engineering, it also help to deeply understand the rheological nature of the polymer solution and the mixing mechanisms of the mechanically agitated tank.