The Action Of Depleted Layer Effect And Viscoelastic Effect On Polymer Sweep Coefficient

The appearance, the characterization method, the influence factors and the variation laws of polymer solution's depleted layer effect and viscoelastic effect in porous media are studied systematically through the measurement of polymer solution's rheological behaviors and viscoelastic behaviors and the seepage tests of polymer solutions in porous media. The mechanism and the extent of action of polymer solution's depleted layer effect and viscoelastic effect on displacement efficiency and sweep coefficient are studied through the displacement tests of polymer solutions in various models.The rheological behaviors of both HP AM solutions and xanthan solutions are measured by means of a rheometer. The influence of such factors as concentrations, relative molecular weights, brine salinities for preparing polymer solutions, temperatures, product forms and filtering conditions on the rheological behaviors of polymer solutions are investigated. Several common xanthans at home are evaluated and Flocon 4800 is selected to do core flow tests and displacement tests.It is discussed that Maxwell model can be used to describe stress relaxation tests and dynamic mechanical tests, and that molecular theory may also be used to calculate the relaxation time of polymer solutions. The results of dynamic mechanical tests display that the viscoelasticities of HP AM solutions increase with the increase of concentrations or relative molecular weights or the decrease of salinities. The viscoelasticities of xanthan solutions also increase with the increase of concentrations. No obvious difference exists between the energy-Storage moduli and the loss moduli of both types of polymer solutions.The curves that pressure differences vary with flow rates in various conditions are measured when HPAM solutions and xanthan solutions flow through porous media. The curves that residual resistance factors vary with flow rates in various conditions are also measured. The experiment results show that the pressure differences of HPAM solutions increase quickly with the increase of flow rates, which shows the existence of viscoelasticity. However, no such a phenomenon exists for xanthan solutions. No obvious variation occurs for the residual resistance factors of HPAM solutions when flow rates vary, while the residual resistance factors of xanthan solutions decrease with the increase of flow rates. New models which contains residual resistance factors for calculating apparent viscosities and sheer rates are given. A simple constant is used to replace the constant term which contains power index in the previous modesl for calculating sheer rates. The rheological curves of HPAM solutions through porous media rise with the increase of concentrations, relative molecular weights or permeabilities. The curves rise quickly when sheer rates are higher. No greater difference exists for the rheological curves of xanthan solutions through porous media when the concentrations are higher than the overlap concentration. The apparent viscosities of xanthan solutions increase with the increase of permeabilities. The rheological curves of xanthan solutions always decrease with the increase of sheer rates.The depleted layer effect of polymer solutions in porous media is discussed. Two-fluid modeland linear model for calculating depleted layer effect are settled, then specific calculating methods for calculating the depleted layer effects of HPAM solutions and xanthan solutions are given. The calculating results show that two-fluid model's calculation is simpler and more reasonable. Both HPAM solutions and xanthan solutions own larger depleted layer thicknesses when the concentrations are lower than the overlap concentration. When the concentrations are higher than the overlap concentration, as the concentrations increase, the depleted layer thickness of HPAM solutions decreases, while the depleted layer thickness of Flocon 4800 solution vary little. Depleted layer thickness has nothing to do with permeabilities so that the relative depleted layer thi...