Migration in Porous Media Flow

Significance

Indicates voids; space available for retention of clogging material. Termed the effective size for filter sands.

The ratio of the 60% size to the 10% size is an indicator of the uniformity.

For a given material, indicates the closeness of packing and propensity for material movement under stress. Relates to surface-active phenomena and adsorption rate. Affects shape of pores and thus fluid-flow patterns. Affects retention of suspension on the particle surface. Propensity for entrapment or filtration of suspension. Negatively charged surface grains will attract a suspended particle with a positive charge.

Shear forces and fluid resistance to flow.

Mixing effects when different densities are involved; may affect direction and rate of flow. Hydrodynamic forces on the medium and suspension. Driving force moving the liquid and suspension into and through the medium.

Material available for inflow, retention, and through-flow. Ability to pass through pore openings. Effect on retention or through-flow due to orientation. Attraction or repulsion to medium or intermediate materials.

Source: U.S. EPA, Assessing the Geochemical Fate of Deep-Well-Injected Hazardous Waste: A Reference Guide, EPA/625/ 6-89/025a, U.S. EPA, Cincinnati, OH, June 1990.

It is possible for complex metals ions that are adsorbed onto very small particles of clay to migrate as metal-clay particles. Laboratory experiments found that radioisotope-clay particles at a low salinity were retained in a sand core, but passed through it at a high salinity.44 Clay-metal particles would not be expected to travel long distances in deep-well reservoir rocks because the pores would be too small.

Injection of highly acid or alkaline wastes has the potential to dissolve some reservoir rock to create channels that would allow more distant transport of small particles. Table 20.11 summarizes the various physical parameters that affect particle migration in porous-media flow.

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