
Direct Quantification of Dynamic Effects in Capillary Pressure for Drainage–Wetting Cycles
Author(s) -
Sakaki Toshihiro,
O'Carroll Denis M.,
Illangasekare Tissa H.
Publication year - 2010
Publication title -
vadose zone journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.036
H-Index - 81
ISSN - 1539-1663
DOI - 10.2136/vzj2009.0105
Subject(s) - wetting , saturation (graph theory) , outflow , capillary action , drainage , mechanics , capillary pressure , porous medium , materials science , chemistry , geotechnical engineering , soil science , porosity , composite material , mathematics , geology , physics , ecology , oceanography , combinatorics , biology
The constitutive relationship between capillary pressure ( P c ) and wetting fluid saturation ( S w ), or retention curve, is needed to model multiphase flow in porous media. This relationship is usually measured under static conditions; however, transient flow is governed by a dynamic relationship between the P c and S w Differences in P c measured under static and dynamic conditions are due to dynamic effects typically defined as a product of a dynamic coefficient (τ) and the rate of change in S w To date, relatively few experimental studies have been conducted to directly quantify the magnitude of this effect. In this study, the magnitude of τ was quantified by measuring both static and dynamic retention curves in repeated drainage and wetting experiments using a field sand. The 95% confidence intervals for the static retention curves showed that the dynamic retention curves were statistically different. The measured τ for primary drainage generally increased with decreasing S w The measured τ values were also compared with those estimated using a different approach based on redistribution time. The measured and estimated τ were in close agreement when the redistribution times were 146 s for the wetting cycle and 509 s for primary and main drainage cycles. The shape of the τ– S w relationship was largely controlled by the slope of the static retention curve. Numerical modeling demonstrated that a log‐linear model relating τ and S w yielded the best match to experimental outflow results.