Understanding the Differences between Air-Water and Organic Liquid-Water Systems for Measurement of Dynamic Capillary Effects in Porous Media
Abstract
Capillarity arises when immiscible fluids exist in porous media. Capillary pressure is equal to the pressure difference between the non-wetting and wetting phases under equilibrium conditions. It is observed that capillary pressure may vary when dynamic flow occurs, and the corresponding pressure is sometimes referred to as a dynamic capillary pressure. The observed flow-rate dependence of capillary pressure measured during drainage and imbibition is referred to as a dynamic capillary effect. Dynamic capillary effects may have implications for many practical problems involving movement of immiscible fluids in the subsurface. A number of experimental investigations have been carried out to quantitatively evaluate the magnitude of dynamic capillary effects. However, the magnitudes of dynamic capillary effects reported to date have been inconsistent, varying by orders of magnitude. Furthermore, while previous studies have examined both air-water and organic liquid-water systems, the reasons that cause observed differences between the two types of system remain uncertain. This study aims at understanding the impact of different saturation profiles caused by different fluid combinations on the measurement of dynamic capillary effects. Experiments were conducted using a custom-designed rapid capillary pressure-saturation (Pc-S) measurement system. The system is based on an automated method previously developed by the authors, and adds fluid-selective pore-pressure micro-sensors with extremely fast response, as well as a soil moisture probe in some cases. Dynamic Pc-S relationships in both air-water and organic liquid-water systems at a range of different rates were obtained. Saturation change with time and related relationships were then examined to understand the difference between gas-water and liquid-water systems in terms of dynamic response, and the implications for these differences on dynamic capillary effects measurement. A numerical simulator was used to model flow behaviors in both fluid systems under dynamic conditions on the basis of experimental parameters. Results suggest that there are differences between gas-water and liquid-water systems that influence the magnitude of measured dynamic capillary effects. Implications for the impact of scale on measured dynamic capillary effects are discussed.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.H51G1435H
- Keywords:
-
- 1829 HYDROLOGY / Groundwater hydrology;
- 1866 HYDROLOGY / Soil moisture;
- 1875 HYDROLOGY / Vadose zone