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Measurements of relative permeability-saturation-capillary head relationships (kr−S−h c) during unsteady state displacement of water by air in soil cores reveal several unique behaviors that have not been previously described. Extremely low air relative permeability (kra) was observed, which increased independent of saturation, by up to an order of magnitude to approach Brooks-Corey kra(S) estimates. These effects were more extreme at faster displacement rates and are inferred to reflect the development and subsequent breakthrough of pore scale dead-end air fingers, which initially do not conduct air flow. Furthermore, kra(hc) estimates tended to be accurate, and where low kra(S) was observed, hc(S) was significantly below moisture retention data. Where kra(S) approximated Brooks-Corey estimates, hc(S) approximated moisture retention data. A calculated backbone (conductive) air saturation, which is the total air saturation minus the dead-end air saturation, was found to control both kra and hc. Generally, water relative permeability data followed common functional relationships. |
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