A Study on Parameter Identification of Pore-Throat Network Model, Derivation of Conductivity Curve and on the Two-Phase Flow within the Dynamic Regime
Date Issued
2004
Date
2004
Author(s)
DOI
922211E002083
Abstract
This study establishes a Unit-Pore-
Throat Ensemble Model (UPTEM). It mimics
the soil pore structure by many pore-throat
units of different sizes which are not
connecting to one another. Methodologies are
developed to estimate the parameters of size
distributions of pores and throats. They
utilize the water-air soil experiment data of
capillary pressure (Pc) and saturation (s)
during primary drainage, primary imbibition
and secondary drainage processes. The
objective is to make the UPTEM
hydraulically equivalent to the actual
water-air-soil system. Provided with the
UPTEM parameters, the Pc-s scanning loops
of water-NAPL two-phase fluids within the
same soil can be inferred without doing the
characteristic-curve experiments.
The equilateral triangle throats and
cubic pore morphology of pore-throat units
enable the UPTEM to simulate the ink-bottle
effect. The simple geometry and
interconnected pore-throat edges make easy
the positioning of fluid-interface balanced
with the capillary pressure using Laplace
Equation, as well as calculating the critical
position and capillary pressure for interface
displacement. Knowing the interface position,
conductivity in addition to wetting- and
non-wetting- phase saturations can be
computed. In direct problems, UPTEM can
reproduce the hysteresis effect and quantify
the trapping ratio on macro-scale. For the
displacement criteria are derived from fluid
mechanic principles and morphology of
pore-throat units, UPTEM can demonstrate
the effect of contact angle on characteristic
curves explicitly. The ensemble design of
pore-throat units avoids the difficulties
caused by size effect and the need to estimate
joint distribution of network pore-throats in
inverse problems. For the same reason, the
size distribution parameters are more directly
linked to the Pc-s curves.
Fitting the drainage and imbibition Pc-s
curves with UPTEM was tried with
application of different ‘throat’ and ‘aspect
ratio’ distribution types. It is shown that
using a simple one-to-one relationship
between the two variables, the model can
match the data reasonably well. The
drawbacks of the UPTEM model are tedious
calculation and over-simplified parameter
estimation methodologies. Future research is
needed for further improvement.
Subjects
Porous medium
non-aqueous phase liquid (NAPL)
two phase flow
characteristic curves
hysteresis
non-wetting phase residuals
Unit-pore-throat Ensemble Model
displacement mechanism
inverse problem
Publisher
臺北市：國立臺灣大學土木工程學系暨研究所
Type
report
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