Observation and analysis of a pronounced permeability and porosity scale-effect in unsaturated fractured tuff
- Walter A.
- Yunjung
- Vittorio
- Daniel M.
- Velimir V.
Over 270 single-hole (Guzman et d., 1996) and 44 cross-hole pneumatic injection tests (Illman et al., 1998; Illman, 1999) have been conducted at the Apache Leap Research Site (ALRS) near Superior, Arizona. They have shown that the pneumatic pressure behavior of fractured tuff at the site is amenable to analysis by methods which treat the rock as a continuum on scales ranging from meters to tens of meters, and that this continuum is representative primarily of interconnected fractures. Both the single-hole and cross-hole test results are free of skin effect. Single-Role tests have yielded estimates of air permeability at various locations throughout the tested rock volume, on a nonind support scale of about 1 m. The corresponding log permeability data exhibit. spatial behavior characteristic of a random fractal and yield a kriged estimate (Fig. 1) of how these 1-m scale log permeabilities vary in three-dimemional space (Chen et al., 2000). Cross-hole tests have been analyzed by means of a thee-dimensional inverse model (Vesselinov et al., 2000) in two ways: (a) by interpreting pressure 1n:ccirds from individual borehole monitoring intervals, one at a time, while treating the rock as if it was spatially uniform; and (b) by using the inverse model to interpret pressure records from multiple tests and borehole monitoring intervals simultaneously, while treating the rock as a random fractal characterized by a power variogram. The first approach has yielded equivalent air permeabilities and air-filled porosities for a rock volume characterized by a length-scale of several tens of meters. Comparable results have been obtained by means of type-curves (Illman and Neuman, 2001). The second approach mounts to three-tlimensional pneumatic tomography, or stochastic imaging, of the rock. It has yielded a high-resolution geostatistical estimate of how air permeability and air-filled porosity, defined over grid blocks having a length-scale of 1 m, vary throughout the modeled rock volume (Fig.2). These tomographic images are compwable to those obtained by the kriging of 1-rn scale log permeability data from single-hole tests (Fig. 1). The results reveal a highly pronounced scale effect in permeability and porosity at the ALRS. We analyze the scaling of permeability at the site on ihe basis of a recent theory, which is consistent with our representation of the rack as a random fractal.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 975149
- Report Number(s):
- LA-UR-01-1122; TRN: US1002395
- Resource Relation:
- Conference: "Submitted to: Conference on Fractured Rocks, March 26-28, 2001, Toronto"
- Country of Publication:
- United States
- Language:
- English
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