Miscible Displacement of Polymers in Porous Media

Abstract

Abstract The results of experiments carried out to explore the dynamics of fluid-fluid displacement in a one dimensional (cylindrical) and bidimensional porous medium are presented. The isotropic porous media consist of glass spheres packings. In a first step, the miscible displacement of water by a polymeric dispersion (xanthan) was studied. In this case there is no hydrodynamic instability in the fluid flow. The originality of the measurement consists in the fact that the polymer molecule was tagged with a γ tracer. The technique used allows us to obtain concentration values of polymeric dispersion, proportional to activity, in terms of time and position of planes perpendicular to the cylinder axis. Transversely averaged concentration profiles were adjusted with the solution of the convection-dispersion equation modified by the presence of dead and retention zones. To study the fraction of retained polymer and the presence of instabilities, the sweep of polymeric dispersion was followed by another of water. Anomalous decreasing concentration profiles were obtained. In order to analyze the viscous instabilities, experiments were performed inside a bidimensional porous media. This miscible displacement process was studied by means of visualization techniques (video-photography). Porous media with two different grain size and a wide range of viscosity ratios and flow rates were used. In all cases the sample was first saturated with polymer dispersion at different concentration and then flooded with water. A rich variety of patterns was found and the results obtained show the crucial influence of fluid viscosity ratio in the resulting structure. For values larger than 100 a fractal behavior appears. A growing law of the fingers length was found and the fractal dimension was measured with different methods. The concentration profiles as a function of time were analyzed. The results obtained are an original contribution to the understanding of the highly complex phenomena occuring during enhanced oil recovery.