Calculation of IPR Curves of Oil Wells for Polymer Flooding Reservoirs

Abstract

Abstract Study of the inflow performance relationship of oil wells for polymer flooding reservoirs is the basis of the analysis of oil well production behaviors, design of production equipment and management of production system. During the polymer flooding, the produced fluid that contains the polymer solution in oil wells obviously shows characteristics of non-Newtonian fluid. Because of degradation, adsorption and retention effects, the rheology of the fluid in formation is various in the different places of the reservoir, so previous IPR equations can't be used to estimate accurately the inflow performance relationship of the oil well for polymer flooding reservoirs. Based on the principle of rheology and percolation flow through porous media, a group of differential equations that describe the flow behavior of the mixture of polymer solution and oil through the porous medium are set up. Based on the experiment results, the critical equivalent shear rate of fluid behaving viscoelasticity in porous media is analyzed. The model is solved for the power-law fluid and the viscoelastic fluid occurred simultaneously in the formation, i.e. a viscoelastic fluid in the very vicinity of wellbore and a power- law fluid in the back of formation, then the IPR curves are drawn. The effect of the changes of fluid rheological parameter on the shape of IPR curves of oil wells is analyzed. Using the data of Daqing oil field flow-after-flow test of one well in the polymer flooding reservoir, the IPR curves are drawn using the method presented in the paper. The flowing BHPs calculated are consistent with the actual measured data. The maximum absolute error is - 0.23MPa and the maximum relative error is 5.82%. Introduction After many years of field tests, it has been proved that polymer flooding is an EOR method with great developing potential in Daqing oil field. Up to now this technique has stepped into industrial application stage. There is no doubt that many new problems will be encountered in the course of producing crude oil mixed with polymer solution. The prediction of oil well IPR curves is one of the methods that solve these puzzles and key problems in polymer flooding technique. During water-flooding development phase, we generally treat the oil-water mixture as Newtonian fluid. However, during polymer flooding process, because the flow behavior and the transmission characteristic of polymer solution are restricted by its rheological properties when it flows through porous media, it makes the fluid properties much more complicated than that in water flooding. Since the end of 1960's, many foreign experts have studied the rheological properties of polymer solution systematically and deeply from the point of structural rheology and have established some constitutive equations which adapted to describe rheological characteristics of polymer solution, such as Cross, Meter, Carreau, Ellis, power-law models, etc. But, all of them are unsuitable to describe the percolation flow behavior of polymer solution through porous media, because the variation of the p parameters along flow direction and the elastic effect are not considered. Sampling analysis in the oil field shows that fluid produced from polymer flooding oil wells obviously appears to be non-Newtonian characteristic, and thus conventional methods of calculating IPR curves of oil wells can't be used in such wells. This paper considers the variation of rheological properties of fluid produced and its basic flow behavior for polymer flooding reservoirs on the basis of core displacement and rheological property experiments. The rheological properties of the in-situ fluid and its change rules along the flow direction have been determined and the critical equivalent shear rate is analyzed when in-situ fluid appears to be viscoelastic fluid. P. 969^