Capillary pressure characteristics necessary for simulating DNAPL infiltration, redistribution, and immobilization in saturated porous media

Abstract

[1] This study presents a capillary-pressure saturation (P C -S) constitutive model that incorporates the capillary phenomena necessary for simulating the spatial distribution of nonwetting fluid migrating in a saturated porous medium. To develop a model validation data set, a sequence of dense, nonaqueous phase liquid (DNAPL) pools were emplaced, under alternating drainage and imbibition conditions, in a one-dimensional, 1 m tall, saturated sand pack. A light transmission/image analysis system successfully distinguished between connected-phase and residual nonwetting fluid in the apparatus, thereby permitting the accurate measurement of DNAPL pool heights. These heights are found to depend on the nonzero capillary pressure across the fluid-fluid interface at the top of the pool. The terminal pressure is demonstrated to be the minimum sustainable capillary pressure in connected-phase nonwetting fluid experiencing imbibition, below which residual is formed. Additional bench-scale experiments demonstrate that a nonwetting phase pool will penetrate an underlying capillary barrier when the entry pressure is exceeded and that the resulting infiltration will terminate when the capillary pressure at the barrier reduces to the terminal pressure. At the macroscopic scale the terminal pressure corresponds to the extinction saturation (i.e., zero nonwetting phase flow) at the inflection point on the imbibition P C -S curve. A ratio of terminal to entry pressure of approximately 0.6 is found to apply at both bench and macroscopic scales and to be independent of porous media and fluid properties. The developed P C -S constitutive model, which extends the Brooks-Corey function to incorporate the terminal pressure, successfully predicted the behavior observed in the laboratory experiments. Constitutive models that do not incorporate both an entry and a terminal pressure, such as those based upon the standard van Genuchten function, are demonstrated to be unable to predict the observed equilibrium DNAPL pool heights in homogeneous media or above capillary barriers.

Self-sustaining smouldering combustion of coal tar for the remediation of contaminated sand: Two-dimensional experiments and computational simulations

“…In this context, air is the nonwetting phase and coal tar is the wetting phase. The model incorporates 19 capillary pressure-saturation-relative permeability relations validated against one [31,32] and two-20 dimensional laboratory experiments [33]. In this application, the model predicts the evolution of air 21 velocity vectors in 2D accounting for, amongst other things, the influence of local NAPL (fuel) content on 22 local effective permeability to air.…”

Organic liquid mobility induced by smoldering remediation

“…In this system, organic liquid is the wetting phase and air is the non-wetting phase. Capillary pressure-saturation-relative permeability functions close the system of equations [33,34]. The pressure and saturation distributions are solved as a function of height and time within the column, subject to inertial, gravity, and capillary forces and subject to the influences of soil permeability, multi-phase relative permeability, and fluid viscosities.…”

“…A one-dimensional version of the finite difference, two-phase flow model DNAPL3D [33][34][35][36][37] was employed. The model solves the organic liquid and air mass conservation equations, which include Darcy's Law, fluid incompressibility assumptions, the capillary pressure definition PC = PA -POL, and the fluid saturation relationship SOL + SA = 1.0:…”

Hydraulic Displacement Of Dense Nonaqueous Phase Liquids

“…The measured residual DNAPL saturations ranged from 1 to 29% of pore space. Further discussion of capillary pressure-saturation relationships is provided by Brooks and Corey (1966) and Gerhard and Kueper (2003a).…”