An Experimental Examination of the Relationship between Fluid Properties and Dynamic Capillary Effects During Drainage and Imbibition
Abstract
Reported measurements have long observed an apparent flow-rate dependence of capillary pressure at a given saturation during dynamic drainage or imbibition. This phenomenon is often referred to as a dynamic capillary effect. While the existence of dynamic capillary effects may have significant implications for the movement of immiscible fluids in porous media across a wide range of practical problems, experiment-based quantitative information about the magnitude of dynamic capillary effects is sparse, and proposed dependencies on system properties reported to date have been contradictory. The purpose of the work conducted here was to study how the dynamic capillary coefficient, τ (a ratio of the difference between dynamic and static capillary pressures and the negative change of saturation with time), is influenced by changes in fluid properties in 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, reducing the potential for sensor-response artifacts which can mimic dynamic capillary effects. For this work, experiments were conducted to quantify τ and corresponding confidence intervals at hundreds of individual saturation values during both dynamic secondary drainage and imbibition. Experiments have been conducted with different fluids selected to vary surface tension and viscosity, both together and independently. Implications for multiphase and unsaturated flow in porous media will be discussed.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.H23C1288H
- Keywords:
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- 1831 HYDROLOGY / Groundwater quality;
- 1832 HYDROLOGY / Groundwater transport;
- 1866 HYDROLOGY / Soil moisture;
- 1875 HYDROLOGY / Vadose zone