Dynamic Distribution Of Rheological Properties Of Temperature-Resistant And Salt-resistant Polymer Solutions In Oil Reservoirs

In polymer flooding,predicting the actual performance of polymer solution reaching the depth of reservoir is key to optimizing polymer flooding scheme and improving polymer flooding effect.It is also a theoretical and technical difficulty that has not yet been solved.In response to this problem,using pore throat model and long core physics simulation experiment method,a study is made on mechanism and prediction method of dynamic viscosity distribution in the reservoir of temperature-resistant and salt-resistant polymer solutions.According to the experimental results,main factors of polymer thermal oxidation degradation of polymer in the reservoir is temperature,aging time and dissolved oxygen.The thermal oxidation degradation of HJ polymer in reservoir mainly occurs in the layer within 10 m of injection well.A quantitative evaluation method for polymer extensional degradation and shear degradation in pore-throat model is established,and it is revealed that the main mechanical degradation mechanism of polymer in pore throat is extensional degradation.The viscosity loss of polymer solution caused by extensional degradation monotonically increases with extensional rate,and there is a "critical extensional rate" at which polymer molecules begin to degrade sharply and an "ultimate extensional rate" at which the mechanical degradation reaches a limit value.These velocity characteristic values can be used as performance indexes for evaluating anti-mechanical degradation of the polymer used for flooding;the model for viscosity loss of polymer in pore throat is established.Through the serial pore throat model degradation experiments,it is found that the polymer can quickly reach the mechanical degradation limit through a few pore throats.It is concluded that mechanical degradation of the polymer occurs mainly in the near-well reservoir.The results of mechanical degradation experiments in core indicate that main factors of mechanical degradation of the polymer in the reservoir are injection rate,transport distance and reservoir permeability;the viscosity loss of polymer solution due to mechanical degradation increases with increasing injection rate,increasing transport distance,and decreasing permeability;according to the law of mechanical degradation of HJ polymer in core,the “critical extensional rate” of HJ polymer in porous media is determined.The mechanical degradation of HJ polymer in the reservoir occurred mainly within 6.5 m from the injection well,and the viscosity loss caused by mechanical degradation is 42%.Based on results of the study on factors and laws of viscosity loss of polymer solution in pore-throat model and core,An empirical model is established to comprehensively characterize dynamic distribution of apparent viscosity of polymer solution affected by thermal degradation,chemical degradation,mechanical degradation and retention in the reservoir.The model is used to predict dynamic distribution of apparent viscosity of polymer solution in the reservoir.The prediction results show that apparent viscosity of polymer solution decreases sharply from injection well to oil well;the rate of viscosity reduction slows down with increasing injected PV of polymer solution;when the local PV number reaches 4 PV,the apparent viscosity of HJ polymer solution reaches a stable value of about 45% of the original viscosity at the position 10 m from injection well.