When developing water-flooding reservoirs, oil and water are regarded as Newtonian fluids in the study of inflow performance relationship of oil wells. But for polymer-flooding reservoirs, prediction of inflow performance relationship of oil wells must consider non-Newtonian behavior of the polymer solution. Based on present papers, descriptions about the flow behavior of non-Newtonian fluid in porous media are mainly concentrated on power-law fluids. These studies do not consider the variation of rheological parameters along seepage flow direction and also elastic effect of polymer solution, therefore these models or results can not be used to characterize the seepage behavior of polymer solution in porous media and predict the inflow performance relationship of oil wells in polymer flooding reservoirs.
Analysis of the samples from oil wells in polymer flooding reservoirs shows that polymer solution produced still appears visco-elastic effect even at a lower concentration of the polymer solution. In this paper, according to a great quantity of experiment data on core displacement and rheological property, a model about the variation of rheological parameters along the seepage flow direction is developed. A constitutive equation for visco-elastic fluid is constructed, in which the variation of the rheological parameters of polymer solutions in porous media is taken into account. A formula of critical elastic flow velocity is presented. Using the constitutive equation proposed in this paper, the seepage flow behavior of visco-elastic fluid with variable rheological parameters is investigated. A model for calculating IPR of oil well in polymer flooding is developed, in which variation of in-situ fluid rheological parameter, visco-elastic effect, formation damage near the wellbore, decrease in formation permeability and other factors are considered. This model is solved using finite difference method and IPR curves and pressure distributions are predicted. Some factors affecting inflow performance are analyzed. With this model, inflow performance relationship of two oil wells in polymer-flooding reservoir in Daqing oil field is calculated. The prediction result is coincident with the flow-after-flow data, the average relative error is less than 10%.
According to the predicted IPR results, the pumping equipment and working parameters can be optimized. It is of great significance for designing a reasonable working system for oil wells in polymer-flooding reservoir.