Visualization and analysis of two-phase flows in three-dimensional porous media

摘要

Fluid-fluid displacement processes have been studied in large, transparent, three-dimensional porous media. Transparent porous media are made by filling a glass container with plastic grains and saturating the packing with a fluid that has an index of refraction matching the one of the grains. Any inclusion of a second fluid phase in such a medium can be observed directly. The morphology and growth dynamics of structures generated when a second fluid phase is injected into the transparent porous medium have been studied. The fluids used are immiscible, the invading fluid is non-wetting, and two different classes of flow have been investigated. Comparison has been made to results from stochastic numerical models. The first class is fast displacements in three-dimensional, radial geometry. The two fluids had the same density, and the invading fluid was injected from a point in the middle of the medium. At an intermediate injection rate the invading fluid formed a ramified structure centered around the injection point (Papers 1 and 2). The injection rate was increased in an attempt to reach a regime dominated by viscous effects (Paper 3). At high rates, surprisingly, structures that were quite compact and nearly spherical emerged. Experimentally, additional processes superimposed on the pure invasion-percolation like behavior were observed (Papers 4-5). The invasion structure may pinch off in some pores and parts of the patterns may alternatively drain and refill. In order to study these dynamical processes in more detail, experiments were performed at even lower rates (Paper 5). Draining and refilling occurred in a complex, non-periodic manner. As a result the tip of the structure displayed ''stick-slip'' motion as it advances, with a wide distribution of step sizes. 76 refs.