Stress permeability

Liu, HH J Rutqvist, Q Zhou and G.S. Bodvarsson, Upscaling of nonrutl stress-permeability... 

Figure 2. TOUGH-FLAC simulation of the DST (a) schematics of two-dimensional model geometry (b) conceptual model for stress-permeability coupling (c) normal stress versus aperture relationship for fractures...

UPSCALING OF NORMAL STRESS-PERMEABILITY RELATIONSHIPS FOR FRACTURE NETWORKS OBEYING FRACTIONAL LEVY MOTION... 

A key parameter for modeling T-H-M-C processes is the relationship between in situ stress and permeability. Since this relationship is generally measured at small scales, upscaling is needed for large-scale models. Few studies on upscaling of this relationship have appeared in the literature. In this study, we develop closed-form upscaled normal stress-permeability relationships... 

A smali-scale stress-permeability (or aperture) relationship is generally obtained from laboratory tests on single fractures. As an example, Figure 3 shows measured normal stress-aperture relations for a rock sample collected from the Shellafield site. The observed function can be fitted by ... 

An important step for upscaling the stress-permeability relationship is to relate local permeability (at a 1.56 m scale) to parameters b, bmax. and fracture frequency f. We assume that at the 1.56 m scale, local permeabilities can be considered to result from horizontal and vertical fractures. Different assumptions regarding relations among local permeability and the relevant parameters (f, b and b ,x) will give rise to different upscaling relationships. In this paper, we present two useful relationships. 

Figured. Outline of stochastic stress and fluid flow analysis for upscaling the srrmll-scale (e.g.. 1.56 m x 1.56 m) stress-permeability relation to a gridblock scale for a large-scale model.

Two methods are developed for calculating gridblock-scale stress-permeability relationships. Although the first method is developed by assuming identical properties for individual hactures and spatially variable fracture densities, it can be mathematically shown that the model is also valid for individual fractures with different aperture parameters (e.g., b, and bmu) as long as Rb is the same for individual fractures. 

A BLOCK-SCALE STRESS-PERMEABILITY RELATIONSHIP OF A FRACTURED ROCK DETERMINED BY NUMERICAL EXPERIMENTS... 

Field observations indicate that the stress condition affects the flow characteristics of fractured rock mass (Barton et al., 1995 Ito and Hayashi, 2003 Pusch, 1989). Many laboratory investigations on single fractures also prove that the normal closure and shear dilation can significantly change the transmissivity of fractures (Makurat et al., 1990 Olsson et al., 2001). When it comes to the block scale stress-permeability relationship, the analytical models based on the orthogonal and/or persistent fracture model are available (Bai and Elsworth, 1994). However, analytical solutions do not generally exist for more realistic fracture systems. Furthermore, to the authors knowledge, block-scale study about the effect of shear dilations of fractures on the... 

Permeability measured using He at a constant pore pressure but different effective stresses is shown in Fig. 5. From the figure we can see that Permeability decreases with increasing effective stress. Permeability decreases from 1.3 md to 0.2 md when effective stress varies from 1 Mpa to 6 Mpa at pore pressure of 1.1 Mpa. We can also see that permeability decreases with increasing pore pressures roughly. It decreases from 1.3 md... 

Permeability measured using Nj is shown in Fig. 3. The figure shows that Permeability decreases with increasing effective stress. Permeability decreases from 1 md to 0.1 md when effective... 

It can be seen from the above four Figures 2-5 that (1) Effective stress has important effect to permeability. With increasing effective stress, permeability decreases at the same pore pressure. (2) With increasing pore pressure, permeability decreases for all four kinds of gases at the same effective stress. For this four kinds of gases, permeability decrease about 30-55% when pore pressure rises from nearly 1.1 Mpa to 7 Mpa at effective stress of 1 Mpa. (3) Permeability decreases when measured using He, Nj CH4 and COj in sequence at the same conditions. For example, the permeability is 0.12 for CH4 and 0.04 for COj at effective stress of... 

Permeabihty measured using CH4 is shown in Fig. 7. It can be seen that with increasing temperature, permeability decreases at the same effective stress. Permeability is a httle higher at 35°C than at 40°C and 45°C, at which permeabihty is very close to each other. It is about 0.25 md, when effective stress is 1 Mpa and temperature is at 35°C while it is around 0.20 md at 40°C and 45°C. Permeability measured using COj is shown in Fig. 8. Different from N2 and CH4 permeabihty measured using C02 is quite close to each other at all 35°C, 40°C and 45°C. For example, permeabihty is about 0.08 md, when effective stress is 1 Mpa for all three temperatures. It has the same law with Nj and CH4 when effective stress reaches nearly 6 Mpa permeability gets close to one same value, which is 0.01 Mpa. 

The balance and composition of microbiota is extremely important to modulate the immune system and to influence the development and physiology of the host (Brestoff and Artis 2013). During stress, permeability and the intestinal barrier function are altered. Probiotics are able to reinforce the epithelial barrier, as was demonstrated by different studies (Zareie et al. 2006 Ait-Belgnaoui et al. 

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