PREDICTION OF SINGLE-PHASE TRANSPORT PARAMETERS IN A VARIABLE APERTURE FRACTURE

A single variable aperture fracture plane is the microscopic scale equ ivalent of a pore in a porous medium, with the advantage that it can b e more easily characterized using a deterministic or stochastic descri ption of the fracture aperture. Fracture aperture distributions can be measured in the laboratory for small fractured cores using Computed T omography (CT) Xray scanning to a resolution of about 50 mu m. Using t he small perturbation analysis developed by Gelhar (1987) based on a s tochastic description of the fracture aperture distribution, we predic t the breakthrough curve of a dissolved contaminant in an aqueous phas e flowing through a single natural fracture, from the knowledge of the geostatistical description of the fracture aperture. The results of t he stochastic analysis are compared to experimental results from the a ctual breakthrough curve of a nonsorbing solute flowing through a sing le fracture plane in a granite core at different flow rates, with a fr acture aperture characterized using CT scanning. The measured effectiv e transmissivity is 13% larger than the estimated value, and the measu red dispersivity is 33% larger than the estimated value. Errors introd uced by the boundary conditions, the first order approximation and het erogeneities not sampled by the CT scanner may account for the differe nce. The estimation method may be useful for predicting solute breakth rough at field sites if the required statistics are obtained from hydr aulic and tracer tests at similar sites.