Fracture networks

Zhang K., Wu Y.S., et al. Flow focusing in unsaturated fracture networks a numerical investigation. 2004 Vadose Zone Journal 3 624-633. 

The PF system creates a fracture network by forcing compressed gas into a formation at pressures that cause stress failure. These fractures increase the formation s permeability. Increased permeability can greatly improve contaminant mass removal rates. PF can also increase the effective area that is influenced by each extraction weU and can intersect new pockets of contamination that were previously trapped in the formation. The ARS PF technology is patented and is commercially available. According to the vendor, it has been used at over 135 federal and private sites in the United States, Canada, Japan, and Belgium. 

Fluid extraction from the reservoir occurs simultaneously with re-injection of cold liquid and air. Atmospheric nitrogen and Ar propagate very fast through the fracture network in the reservoir rocks and arrive at producing regions with negligible thermal interference. This may be used as a simple and cheap method to estimate the three-dimensional permeability tensor. 

Montemagno, C.D. and Pyrak-Nolte, L.J. (1995) Porosity of natural fracture networks. Geophysical Research Letters 22, 1397-1400... 

The results of the multiple nonreactive tracer study showed that secondary contaminant sources may form within the bedrock matrix, and that the importance of this source increases with continued contaminant discharge through the bedrock fracture network. This may be particularly important for reactive contaminants such as radionuclides, where matrix diffusion can enhance solute retardation by many orders of magnitude. 

More comprehensive fracture networks are encountered in connection with the major fault zones of the study area. The fracture intensity is highest within the master fault complexes, and particularly along those which were affected by inversion in Tertiary times. 

Fig. 7 is a schematic diagram of the experimental Los Alamos System in New Mexico. Water at 65°C and 1000 psia is pumped into hydraulic fracture network, approximately 3000 ft in diameter and circulated... 

Fig. 7 Experimental configuration and operating conditions Los Alamos hydraulic fracture network. (View this art in color at www.dekker.com.)...

Recent particle tracking simulations in soil network models indicate that solute dispersion is more sensitive to the water retention curve than to the particular combination of pore-size distribution and topology that determine its shape (Vogel, 2000). Numerical particle tracking techniques have also been used to simulate solute dispersion in fractured media. Examples for two-dimensional randomly intersecting fracture networks include the models developed by Hull et al. (1987), Smith and Schwartz (1984), Robinson and Gale (1990), and Clemo and Smith (1997). Recently Nordqvist et al. (1996) and Margolin et al. (1998) have extended this approach to three-dimensional fracture networks. 

Berkowitz, B., and C. Braester. 1991. Dispersion in sub-representative elementary volume fracture networks Percolation theory and random walk approaches. Water Resour. Res 27 3159-3164. Berkowitz, B., and R.P. Ewing. 1998. Percolation theory and network modeling applications in soil physics. Surv. Geophys. 19 23-72. 

Hull, L.C., J.D. Miller, and T.M. Clemo. 1987. Laboratory and simulation studies of solute transport in fracture networks. Water Resour, Res. 23 1505-1513. 

Margolin, G., B. Berkowitz, and H. Scher. 1998. Structure, flow, and generalized conductivity scaling in fracture networks. Water Resour. Res. 34 2103-2121. 

Rowe, R.K., and J.R. Booker. 1989. A semi-analytic model for contaminant migration in a regular two-or three-dimensional fractured network Conservative contaminants. Int. J. Numer. Anal. Meth. Geomechan. 13 531-550. 

Numerically, these processes can be modeled by different techniques, such as finite-difference methods (FDM), finite-element methods (FEM). and discrete-element methods (DEM), as well as discrete fracture network (DFN) methods. In addition, many of the coupled processes are nonlinear, and the... 

Geometrical factors and properties Rock fracture networks and their characterization and representation Rock fracture properties (aperture, roughness, gouge production, filling, conductivity, storativity) Variability and representability of network connectivity... 

In the DECOVALEX I project, modeling was conducted on three hypothetical BMTs and six TCs, involving three small laboratory tests of rock samples and fractures, and three large field tests. Details may be found in Jing et al. (1995). One of the BMTs simulated a Swedish KBS-3 disposal concept in a fractured granitic rock with a fracture network system and properties similar to those of the Stripa granite. This case will be presented in more detail in section 5. 

This BMT was a well-defined near-field problem, with both a realistic fracture network (which may likely be encountered in practice) and complete aspects of coupled THM... 

The nature of a BMT study is well demonstrated with BMT3 of the DECOVALEX I project. It was a problem associated with a near-field repository model, set up as a two-dimensional plane-strain problem in which a tunnel with a deposition hole was located in a fractured rock mass. The model is 50 X 50 m in size, and situated at 500 m below the ground level (Figure 1). The fracture network is a two-dimensional realization of 6,580 fractures from a realistic three-dimensional fracture network model of the Stripa Mine, Sweden (Figure 2). The problem is set up as a fully coupled THM near-field repository problem, with thermal effects caused by heat release from radioactive waste in the deposition hole (the heater). Heat output decreases... 

Figure 2. Reference fracture network from Stripa Mine for BMT3 (DECOVALEX I)...

Vertica) symmetry and simplified fracture network Nkith 295 fractures, 337 blo, 1540 finite difference elenteots. and >0853 nodes A small inner region with random fractures and lager outer region with tegular artificial fractures... 

CNWRA (NRC, USA) UDEC Dem with simplified fracture network... 

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