Study on the Influence of Clay Minerals on Viscosity of Polymer Solution and Flowing Characteristics: A Case Study from Bohai SZ36-1 Oilfield

When polymer flooding agent flows through porous media, it will inevitably contact with reservoir fillings, and retention will occur because of hydrodynamic trapping, mechaincal trapping, surface adsorption and interaction of polymer molecules. The physical and chemical reactions will not only affect flowing characteristics of injected fluid, but also impact adhesive properties of crosslinking polymer. Based on the theories of rock mineralogy, physical chemistry and polymer materials, by means of instrumental detection, chemical analysis and physical simulation, study has been conducted on the main clay minerals in sandstone reservoir and polymer interaction and experiment study on the influence of clay type and its content on viscosity, adsorption capacity and flow characteristics of polymer gel has been carried out. The results showed that three kinds of clay minerals including montmorillonite, kaolinite and illite could reduce the viscosity of polymer solution and gel in different levels because of great differences in absorption capacity, of which montmorillonite is the largest, followed by kaolinite and illite. The difference of crystal layer structure is the direct reason for this kind of difference. Compared with the polymer solution, the clay minerals is smaller in adsorption capacity of crosslinking polymer solution. During sampling inspection on polymer concentration, polymer concentration in the upper liquid of container is usually lower than that of lower liquid, but the overall level is insignificant. Further analysis has showed that the adsorption of clay minerals has leaded to the increase of polymer retention in pores, reducing the flow section, and increasing in the resistance coefficient and residual resistance coefficient. In addition, migration and trapping of clay particles in porous media might also increase seepage resistance.