Earth Sciences Division
Research
Fundamental and Exploratory Research Program
Objectives
L ab o ra t o ry fl ow experiments on transparent fra c t u re replicas perm i t direct visual investigation of fl ow p rocesses and identification of controlling mechanisms of large r - s c a l e phenomena that are critical in many areas. These include flow and transp o rt around repositories for high-level nu clear wastes, contaminant migration and remediation and enhanced p e t roleum re c ove ry. Fra c t u re fl ow visualization ex p e riments have been conducted in parallel rough surfa c e glass plates and fracture casts made with epoxy resin. Rough glass plates do not represent actual natural fractures, but can provide wa t e r - wetting ch a ra c t e ristics similar to many rock surfaces. On the other hand, e p ox y fra c t u re casts can provide re a s o n ably accurate reproductions of natural fract u re aperture fi e l d s , but have hydrophobic surfaces. For some purposes it is desirable to combine the wetting ch a ra c t e ristics of glass with the fra c t u resurface topography reproduction obtained through casting. Glass casts have the combined adva nt ages of closely reproducing natural f ra c t u re surface roughness and of being tre a t able to provide the wide range of we t t abilities found for natural rock surfaces. H e re we present a new method for replicating natural rock surfaces using molten glass.
Glass Casts of Rock Fracture Surfaces: A New Tool for Studying Flow and Transport Jiamin Wan, Tetsu K. Tokunaga, Thomas R. Orr, Jim O’Neill and Robert W. Connors
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Contact: Jiamin Wan 486-6004, jmwan@lbl.gov
Figure 1. Photographs of the surface of a granite fracture (a), and its glass cast (b). Both are 120 x 160 mm.
Annual Report 1998-1999
burning off the wax positives. In step four,glass fracture casts (positives) are made from the investment molds.The final step entails finishing the glass fracture replicas. Five sides (4 edges and back) of each half cast are ground and polished as a pair. The topography of a glass cast surface was compared with that of the o ri ginal rock fracture using laser profilometers and an atomic force microscope (AFM). For coarse-scale measurements, surfaces were pro filed with an LK-081 CCD laser displacement sensor (Keyence Corp., Wo o d cl i ff Lake, N.J.) mounted on a Vi ew Precis 3000 coordinate measuring machine (Vi ew E ngineering Division, G e n e ra l Scanning, Inc., Simi Valley, Calif.). For higher resolution measurements over smaller areas and narrower topographic ranges on rock and glass casts, a UBM laser (UBM, Sunnyvale, Calif.) was used.The UBM laser has a spot size of 1 µm, a z measurement range of 100 µm, and a z resolution of 0.06 µm.This system was also used to obtain surface pro files on the roughened quartz glass samples. For higher resolution topography, small areas of glass casts were scanned with an AFM (Autoprobe M5, Park Scientific Instruments, Sunnyvale, Calif.). We used this AFM in the standard contact scanning mode to obtain info rmation on finer-scale topography and also to obtain values of surface roughness for comparison with laser profilometry results.
Approach Results The glass fracture pairs reported in this paper were cast from two different original rock fractures. The larger (120 x 160 mm) glass fracture cast replicated a Swedish gra n i t e . The smaller (70 x 70 mm) cast replicated a fractured gabbro (Dixie Valley,Nev.). The casting procedure involves five steps. In the first step, silicone rubber molds (negatives) are made of each rock slab. In step two, wax patterns (positives) are made from the silicone rubber molds. In step three, investment molds (negatives) are made by
Figure 2. Comparisons of laser surface profiles on the granite fracture and glass cast. These (a) 100 mm and (b) 10 mm long profiles were measured in 50 µm steps.
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One set of casts will be discussed with respect to each characterization of the finished products.The simplest characterization is that of visual comp a risons between an ori ginal ro ck fracture surface and its corresponding glass cast. A photograph of one side of the granite fracture (Figure 1a) and its corresponding finished glass fracture cast (Figure 1b) qualitatively shows reproduction of fracture surface texture and roughness. Reflected light was used for photographing the rock,