Abstract
Fluid mixing in permeable media is essential in many practical
applications. The mixing process is a consequence of velocity
fluctuations owing to geological heterogeneities and mobility contrast
of fluids. Heterogeneities in natural rocks are often spatially
correlated, and their properties, such as permeability, may be described
using fractal distributions. This work models the fractal
characteristics of such permeability fields in which the covariance
function is expressed as a power-law function. A generalized scaling
relation is derived relating various fractal permeability fields using
the magnitude of their fluctuations. This relation reveals the
self-similar behavior of two-phase flow in such permeable media. To that
end, a recently developed, high-resolution numerical simulator is
employed to validate the analytically derived scaling relations. Two
flow problems are considered in which flow is governed by 1) a linear,
and 2) a nonlinear transport equation. Due to the probabilistic
representation of the fractal permeability fields, a sensitivity study
is conducted for each flow scenario to determine the number of
realizations required for statistical convergence. Scaling analysis is
performed using ensemble averages of simulated saturation profiles and
their mixing lengths. Results support the validity of the developed
scaling relation across the range of investigated flow conditions at
intermediate times. The dynamics of linear flow in the asymptotic regime
is affected by the correlation structure of heterogeneity. In nonlinear
flow, scaling behavior appears to be dominated by the degree of
nonlinearity.