A Functional Relationship Between Dynamic Capillary Effects and Saturation
Abstract
Dynamic capillary effects (the apparent rate dependence of capillary pressure during dynamic drainage or imbibition) have significant implications for the movement of immiscible fluids in porous media across a wide range of systems. However, experiment-based quantitative information about the magnitude of dynamic capillary effects is extremely sparse, and proposed dependencies on system properties reported to date have been contradictory. Although it has long been suspected that the magnitude of dynamic capillary effects may vary with both saturation and wetting/drying path, experiments designed to quantify these functional dependencies have not been reported. The purpose of the work conducted here was to examine the functional relationship between the dynamic capillary coefficient, τ (a ratio of the difference between dynamic and static capillary pressures and the negative change of saturation with time) and saturation in a range of unconsolidated porous media. Experiments were conducted with a device designed specifically for the measurements. The device is based on an automated method previously developed by the authors for rapid measurement of capillary pressure- saturation (Pc-S) relationships, but adds custom-designed membrane-based fluid-selective pore pressure micro-sensors for direct measurement of pore pressures. The micro-sensors were developed to have extremely fast response times compared with traditional pore pressure tensiometers. Quantitative flow modeling shows that tensiometer response time can have a strong influence on the experimental measurement of dynamic effects, potentially resulting in experimental artifacts which can mask true dynamic capillary effects and invert measured trends. For this work, experiments were conducted to quantify τ and corresponding confidence intervals at hundreds of individual saturation values during dynamic secondary drainage, based on multiple individual secondary drainage curves. Results of the work point to a strong relationship between τ and S, that is well-correlated with system properties. Implications for multiphase and unsaturated flow in porous media will be discussed.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.H41C0892C
- Keywords:
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- 1829 Groundwater hydrology;
- 1866 Soil moisture;
- 1875 Vadose zone