| Summary: | Dual permeability is introduced as an approach to modeling flow and transport through fractured
media. The approach allows a large reduction in the number of fractures that are represented
explicitly in a discrete fracture network. The most important fractures in terms of fluid flow are
identified using their physical characteristics. These fractures form a sub-network that divides the
entire fracture network into smaller domains. The fractures of the smaller domains are approximated.
The approximations do not rely on continuum assumptions. They are determined individually and
independently for each small domain, resulting in a parallel structure to the calculations.
An exploratory model is developed for steady state fluid flow and solute transport in two
dimensional fracture networks and compared to a discrete fracture model that represents all of the
fractures explicitly. Individual fractures are represented by finite lines with constant hydraulic
transmissivity. Solute transport calculations use particle tracking. The dual permeability model is
shown to provide acceptably accurate solutions while reducing the maximum number of simultaneous
equations by well over an order of magnitude.
The dual permeability approach takes advantage of the hydraulic behavior of highly
heterogeneous media. Channeling of flow that develops in such media is used to reduce errors
introduced through the sub-continuum approximations. The dual permeability approach works better
when the fracture system has a broad range in the scale of fracturing as demonstrated by transport
calculations for fracture networks with a high degree of clustering or with a fractal nature.
A study of sub-REV fracture networks reveals that averaged flow through fractured media can
be represented using tensor notation in much smaller domains than an REV. At these scales,
heterogeneity within a fracture domain causes the tensor representation to be asymmetric, unlike the
continuum representation of granular porous media. Hydraulic heads within a heterogeneous fracture network do not vary in a smooth fashion. The hydraulic head reflects the distribution of heterogeneity
within the domain. The approximations developed for the dual permeability model required that the
boundary conditions imposed on the small domains reflect heterogeneity both within the domains and
external to them. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate
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