Miscible Flooding of Polymeric Solution in Porous Media of Double Porosity
Authors: D&apos;Angelo M.V. , Chertcoff R. , Rosen M. 
Published: December 2007

Abstract
With the aim of study possible mechanical trapping phenomena and adsorption in a double porosity medium we performed two types of experiments:A saline polymer solution which initially saturates a porous medium is displaced with another polymer solution with a different salt concentration (conductivity measurement). In both solutions the polymer used is scleroglucane.A flow of a saline solution into a polymer solution (scleroglucane), which initially saturates the porous media of double porosity (conductivity measurement). At the same time, a flow of a polymer solution marked with a radioactive tracer (gamma emitter) is performed and its displacement can be followed externally to the medium. In both cases, the dispersion profile at the outlet and at each position along the medium are analyzed. The polymer solution rheology was carefully controlled: it is a shear thinning fluid with n=0.6, while ensuring the absence of microgels in the solution.
The porous medium was prepared with an homogeneous poral size distribution, with grains of 500 micrometers diameter and an internal porosity of 30 percent, obtained by grinding sintered glass beads. The experiments were performed with the medium in vertical position.
The first results suggest that the saline solution explores all the poral structure while it is possible that the macromolecules of the polymer solution cannot penetrate into the small pores.
With these experiments we expect to obtain information about the presence of heterogeneities in the bed. However, this information was obtained only in those cases where we change the concentration of the polymer solutions. Finally, we can observe a retention phenomenon, whose interpretation is still controvertible.

Introduction
The dispersion process in a porous media is an analysis tool that allows us to obtain valuable information when studying the problems involved in flow in porous media. Therefore is of great interest at different fields of science and technology, in particular in Oil Recovery. In this process a large amount of oil remains trapped in the flooding zone due to the inmiscibility, the capillary pressure effects and the big viscosity ratio between liquids. For this reason, in certain conditions, miscible displacements as alternative methods are used, like those that involve the use of surfactants, soluble in water and oil1. In other circumstances, polymer solutions are used to improve the viscosity ratio between the displacing fluid and the oil, producing a favourable mobility ratio2 (Eq.1). With the last method, the porous matrix and polymer interaction have to be carefully analysed, because it may occur molecular retention phenomena produced by different mechanisms: adsorption, mechanical impediments due to the size of the molecules or mechanical degradation, and non controlled mechanism due to the rheological properties of the polymer, specially if they are non-Newtonian.
The aim of this work is to contribute to the knowledge of the basic mechanism involved in the dispersion process of miscible fluids, in order to interpret the structural characteristics of the porous matrix and the different ways in which the fluids interact between them and with the porous media. For this reason, we intend to study the dispersion phenomena in a flow of a non-Newtonian polymer in a porous media of a complex geometry, analysing the behaviour of polymer solutions in modelled double porosity porous media, made by microspheres of compacted glass.
In the experiments, we use radiotracer techniques in order to know the evolution of the fluid inside the porous sample and to obtain the distribution of transit times. We also use conductivity techniques, to analyse the global behaviour of the tracer in the porous media.
In this work, in the transport phenomena, the possible geological heterogenities effect (in our case modelled by a double porosity media) are disacoupled of the normal dispersion phenomena. In this sense the "flight time" concept is useful and was introduced by A. Datta-Gupta and Datta-Gupta et al3,4.