Ali ZafaraniSubsurface Processes GroupUniversity of California, Irvine

Groundwater is one of the main resources to provide water consumption needs

Sources of pollution: Chemicals (detergents, petroleum, etc.), Radionuclides, Seawater, Pathogens

Understanding the transport mechanisms of contaminants Designing infrastructures and hydrogeologic systems Designing remediation systems Estimate of damage

Provide pathways for fluid flow Large scale fracture networks Reservoirs formed in fractured rocks Fractures appear in many kinds of

geological systems

Advection Transport of particle with

the flow field

Dispersion (Effective Longitudinal Dispersion) Molecular Diffusion Taylor dispersion Macro scale dispersion

3-D Navier-Stokes Equation

3-D Stokes Equation

2-D Reynolds Equation

Inertial<< viscous and pressure

Changes in fracture aperture are smoothNormal velocity to fracture walls are negligible3-D 2-D

Inertial forces Viscous forces

Pressure term

Momentum Eq.

Mass Conservation

Fick’s first law of Diffusion diffusive flux ~ spatial concentration

gradient

Fick’s second law of Diffusion Changes of

concentration field with time

Diffusion Coefficient [L2/T]

Parabolic distribution of velocity in aperture

~ square mean velocity ~ Mean aperture size

b

V

Dispersion caused by variety of pathways

CCD Camera

Porous media cell

Rotating stand

Uniform lightsource

Textured glass plates provide analog to fracture surfaces.

Rotating test stand holding test cells and equipped with a high resolution 12-bit CCD camera (2048 x 3072 pixels)

x x'

Fracture plate 3/4” flat glass

No flowboundary

Inlet manifold

Aluminum frame

Referencewedge

Clear PVC gasket Confinement pressureinlet

Measured light intensities are used to accurately quantify: Fracture aperture Solute concentrationsat high resolutions over

entire flow field. Measurements can be

used to calculate Solute dispersion

Aperture (cm)

0

0.04

Entrappednonaqueous

phase

3 cm

Constant fracture aperture (smooth walls)

Macro-scale dispersion is zero

Taylor dispersion results the plume to be stretched in flow direction (DL,Taylor)

ApertureAperture00 0.24 mm0.24 mm

10 cm10 cm

Experimental

Simulation

Variable aperture field is measured by image system Finger shaped forefront of solute plume shows the

Macro-Dispersion

Simulation and Experimental results match for Hele-Shaw cell

Simulations underestimate dispersion in Rough-Walled cell

Reynolds equation underestimates variations in velocity field

Network fracture simulation Scale dependent dispersion coefficients