Modeling Subsurface Petroleum Hydrocarbon Transport
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The distribution of phases within the subsurface depends on
- the number of liquids present,
- the relative strength of attraction between the fluids and the solids,
- the geometry of the pore system, and
- the history of the system.
Usually water is more strongly attracted to the solid surfaces than nonaqueous phase liquids. Thus, water is said to be the wetting phase. When placed in an irregular porous media, the water tends to occupy the small pores and grain contacts. The non-wetting phase (the nonaqueous phase liquid) then occupies larger pores and the pore openings. In three-phase systems (water/NAPL/air), air is usually the most non-wetting phase and the NAPL must occupy an intermediate position. This results in the NAPL forming films and small lenses between the water and air. Motion of a phase ceases when it becomes isolated as individual droplets or blobs. Flow occurs only through interconnected pathways in the pore space.
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