A porous medium consists of a connected 3-dimensional solid matrix with a highly ramified network of pores and pore throats in which fluids may flow. Porous media are often characterized in terms of ``pore size distributions" but this does not provide a sufficient description for the calculation of important physical properties such as permeability. A variety of models for the pore space geometry of porous media have been developed. However, simple models that can be used to calculate macroscopic physical properties have not yet been developed. Rudolf Hilfer has developed a new method for characterizing the structure of porous media and transport phenomena in them.
Multiphase fluid flow in real porous materials (and most model porous media)
still defies theoretical understanding. Nevertheless they are of
considerable scientific interest as important examples of pattern formation
under far from equilibrium conditions. The fluid-fluid interfaces and their
evolution can often be described in terms of fractal geometry
and scaling ideas. Better
understanding of multiphase flow phenomena and the implementation of this
knowledge to oil
recovery applications is obviously of major importance in Norway. The physics of porous media
has been the main focus for the Cooperative Phenomena Program for almost 10 years.
From the start the emphasis has been on experiments.
To control experiments on fluid flow, reliable techniques
for measuring bulk properties like viscosity and interfacial
tension are needed. We have developed different Light Scattering techniques
(Chapter 4.2) to meet this need. Constricted geometries also influences
fluid flow in unpredictable ways. We have developed an experimental method (Chapter 4.2)
to observe and map the fluid flow fields using ``tracer'' particles in long
thin quasi 1-dimensional pores. These processes may be considered as the elementary
flow phenomena for porous media.
Christina Søyland and Arne Hovland are further developing and applying this technique in their master degree projects. Unni Oxaal and Eirik G. Flekkøy are collaborating in a study of the effects of an obstacle in a quasi two-dimensional channel on the dispersion of tracer molecules. This project combines experimental studies with computer simulations based on the new Lattice Boltzman algorithms developed by Flekkøy. Marit Døvle is studying dispersion and the structure of flow lines in such a channel when the number of obstacles is increased, and in radial Hele-Shaw cells. Thor Engøy is studying vapor/liquid transport during the drying of the complex, elongated and connected pore structures found in wood materials.
Lars Høier and Stein Malerud are engaged in a project on thermal convection in porous media. As a first step in their master thesis', they investigated how perturbations of the cell walls with high aspect ratios influence the convection roll pattern and how it changes with the aspect ratio.
In his project Aleksandar Birovljev works experimentally on migration and dispersion in porous Hele Shaw cells under low flow rate (invasion percolation limit) conditions. This project includes studies of the effects of a gradient (such as buoyancy or hydraulic gradients) on the migration, fragmentation and coalescence of non-wetting fluids. Liv Furuberg and Gerhard Wagner have been working on the same problems using computer simulations.
A considerable effort has been invested in making transparent
models of porous media by using transparent solid materials for the
matrix and fluids of the same index of refraction.
Vidar Frette has been a driving force in the
development of the three-dimensional transparent models and has used the technique
to study many interesting interface-structures arising in two-fluid
displacement in three-dimensional experiments.
Thomas Walmann has recently (December 1992) completed his Master thesis project
where he carried this strategy further and developed a
(fluorescent) method for mapping the highly ramified interfaces resulting from
the unstable displacement of a ``defending'' fluid by an invading fluid of higher
viscosity in three-dimensional porous materials.