ABSTRACT
ABSTRACT: Fracture skins include both zones of physical or chemical alteration in the matrix adjacent to the fracture and coatings on the fracture surfaces formed by infiltered debris, precipitated minerals, and organic matter. Fracture skins alter the hydraulic and transport properties of the fractured media. Previous studies of solute transport in media with fracture skins are extended by mathematical analyses of steady and transient flows with pulse-and step-functions of conservative (e.g., Cl1) and reactive (e.g., Cs137) tracers. Sensitivity studies are conducted with three dimensionless factors that are functions of fracture aperture, skin thickness, porosities, diffusion coefficients, and retardation coefficients of skin and matrix. Skin diffusion coefficient and porosity are critical factors for both reactive and conservative solutes. The next most important factor for reactive solutes is the retardation coefficient, whereas for conservative solutes it is skin thickness. When the flow is pulsed, back-diffusion is shown to be an important process that increases solute concentration in the fracture. In fractured, crystalline rocks, skins attenuate transport in fractures with porous skins, while less porous skins enhance breakthrough concentrations. Skin types observed in crystalline rocks were clay coatings and weathering rinds, which have different effects on solute transport.
