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Aperture Characteristics, Saturated Fluid-Flow, and Tracer-Transport Calculations for a Natural Fracture

by P. W. Reimus, Los Alamos Natl Lab, Los Alamos, United States,
B. A. Robinson, Los Alamos Natl Lab, Los Alamos, United States,
R. J. Glass, Los Alamos Natl Lab, Los Alamos, United States,



Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1993

Abstract:

We used surface-profile data taken with a noncontact laser profilometer to determine the aperture distribution within a natural fracture and found the surfaces and apertures to be isotropic. The aperture distribution could be described equally well by either a normal or a lognormal distribution, although we had to adjust the standard deviation to 'fit' the data. The aperture spatial correlation varied over different areas of the fracture, with some areas being much more correlated than others. The fracture surfaces did not have a single fractal dimension over all length scales, which implied that they were not self-similar. We approximated the saturated flow field in the fracture by solving a finite-difference discretization of the fluid-flow continuity equation in two dimensions. We then calculated tracer breakthrough curves using a particle-tracking method. Comparing the breakthrough curves obtained using both coarse- and fine-resolution aperture data (0.5- and 0.05-mm spacing between points, respectively) over the same subset of the fracture domain suggests that the spacing between the aperture data points must be less than the correlation length to obtain accurate predictions of fluid flow and tracer transport. In the future, we will perform tracer experiments and numerical modeling studies to determine exactly how fine the aperture data resolution must be (relative to the correlation length) to obtain accurate predictions.

Subject Headings: Fluid flow | Hydraulic fracturing | Probe instruments | Cracking | Correlation | Spacing | Numerical models

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