Migration Characteristics Of Polymer Used For Oil Displacement In Reservoir Pores

The real state and migration mode of the polymer used for oil flooding in the tiny pore throats of the reservoir is an important basis for further revealing the mechanism of polymer flooding.In this thesis,the micro-pore throat model and the quartz sand filling model are used to determine the actual migration mode of polymer molecular clusters in pore throats,and to explore the essential reasons for their high migration resistance and improved sweep efficiency in porous media.The morphological structure of partially hydrolyzed polyacrylamide(HPAM)in water was measured by scanning electron microscopy and dynamic light scattering.The experimental results confirmed the well-known understanding of the macroscopic rheology of polymer solutions-as the polymer concentration increases,the network structure of the polymer in water tends to be denser,and the hydrodynamic radius of the polymer increases,thereby It directly leads to the increase of macroscopic rheological parameters such as apparent viscosity,storage modulus and dissipation modulus of polymer solution measured by rheometer.These results provide a reference for comparative analysis to explore the essential difference between the kinetic behavior of polymers in the micro-pore throats of porous media and their macro-rheological behaviors.The transport experiment of polymer-water system in a single pore throat model was carried out.The ratio of the throat radius to the polymer hydrodynamic radius is defined as the pore aggregation ratio Rtp,which is used to characterize the relative size of the polymer clusters and the pore throat size.The measurement results of dynamic light scattering instrument show that the hydrodynamic radius of commonly used oildisplacing polymers in water is the same or similar to the pore-throat radius of the reservoir,and the polymer-water system is a dispersed discontinuous medium in the porethroat of the reservoir.feature.With the decrease of Rtp,the measured pressure and flow rate of the polymer-water system migrated in the single-pore throat model gradually showed more and more obvious random fluctuations;As a dispersion,the polymer clusters stay and block at the pore throats—breakthrough migration characteristics;when the Rtp drops to about 15,the polymer clusters form stable blockages on the pore throats.This is a very typical mechanical behavior of discontinuous dispersions,which obviously deviates from the macroscopic rheological behavior of continuous media.Most of the measured resistances are much higher than the predicted values of the viscous fluid model and viscoelastic fluid model;the smaller the Rtp,the higher the measured resistance.The higher the probability that the coefficients are higher than those predicted by the viscous and viscoelastic fluid models.The migration characteristics of the polymer-water system in the heterogeneous channel system were studied by using the parallel pore-throat model and the parallel sandpacking model.According to the measured results of the split rate of water and silicone oil in the non-uniform parallel pore-throat model,combined with the results of classical fluid mechanics analysis,it can be determined that the split rate of the fluid as a continuous medium in the non-uniform parallel pore-throat model has nothing to do with viscosity.In the heterogeneous parallel pore-throat model,the split flow rate of the polymer-water system obviously deviates from the theoretical prediction.In contrast to the split rates of water and silicone oil,the abnormal split rates of the polymer-water system in the parallel pore-throat model are not due to its "viscosity" but to the dynamic plugging of polymer clusters.The experimental results of polymer-water system migration in a heterogeneous sand-packing model demonstrate that the blocking effect of polymer clusters leads to a decrease in the diversion rate of relatively high-permeability sand pipes.The results of the polymer-water system flooding experiments in the heterogeneous sand-packing model demonstrate that the plugging effect of polymer clusters leads to higher oil displacement efficiency in relatively low-permeability sand pipes than in relatively high-permeability sand pipes.