Estimating Large‐Scale Fracture Permeability of Unsaturated Rock Using Barometric Pressure Data

Abstract

We present a three-dimensional modeling study of gas flow in the unsaturated fractured rock of Yucca Mountain. Our objective is to estimate large-scale fracture permeability, using the changes in subsurface pneumatic pressure in response to barometric pressure changes at the land surface. We incorporate the field-measured pneumatic data into a multiphase flow model for describing the coupled processes of liquid and gas flow under ambient geothermal conditions. Comparison of field-measured pneumatic data with model-predicted gas pressures is found to be a powerful technique for estimating the fracture permeability of the unsaturated fractured rock, which is otherwise extremely difficult to determine on the large scales of interest. In addition, this study demonstrates that the multi-dimensional-flow effect on estimated permeability values is significant and should be included when determining fracture permeability in heterogeneous fractured media.

Phase‐Field Modeling of Reaction‐Driven Cracking: Determining Conditions for Extensive Olivine Serpentinization

“…From this we extract reference permeabilities in the range of [ K ϕ ]∼10 −17 –10 −13 m 2 , which corresponds to actual permeablities of K ϕ ∼10 −15 –10 −11 m 2 when 1% porosity is assumed. This range is consistent with observed permeabilities in tectonically exhumed mantle peridotites (e.g., Manning and Ingebritsen, ; Wu et al, ; Dewandel et al, ). Assuming a fluid bulk modulus of K f =2.2×10 9 Pa and a reference porosity of [ ϕ ]=0.1 yields a dimensionless compressibility of β ∼5.…”

“…Effective water‐in‐water diffusivities for flow in cracked rocks have been estimated to be ∼2 × 10 −9 m 2 s −1 (Wu et al, ; Wu et al, ; Rudge et al, ). We use this to obtain a value of D ϕ =1×10 −6 kg·m −1 ·s −1 (here representing the diffusivity multiplied by the fluid density ρ f ), which appears in equation .…”

“…Effective water-in-water diffusivities for flow in cracked rocks have been estimated to be ∼2 × 10 −9 m 2 s −1 (Wu et al, 2006;Wu et al, 2010;Rudge et al, 2010). We use this to obtain a value of D = 1 × 10 −6 kg·m −1 ·s −1 Journal of Geophysical Research: Solid Earth 10.1029/2019JB018614 Figure 6.…”

Atmospheric Controls on Gas Flow Directions in a Waste Rock Dump

“…Furthermore, temporal fluctuations in barometric pressure can trigger the mechanism of convection and significantly enhance gas migration (Massmann and Farrier, 1992; Massman and Frank, 2006). Such gas pressure fluctuations within the unsaturated zone due to barometric pressure changes have been used in some studies to determine air permeability in the unsaturated zone (Weeks, 1979; Smolensky et al, 1999; Neeper, 2002; Wu et al, 2006). Barometric flow in boreholes themselves was the subject of studies for the purpose of extracting contaminant vapor (Neeper, 2003; Neeper and Stauffer, 2005).…”

An Integrated Modeling Approach for Characterizing Multiphase Flow, Chemical Transport, and Heat Transfer in Fractured Reservoirs

“…Comparison with Pneumatic Data: Calibration of the 3-D UZ model to pneumatic data or gas flow provides a practical method of estimating large-scale fracture permeability within the 3-D UZ system 19,20 . Note that because of the low percolation flux at the site, moisture data are found to be insensitive to fracture properties under ambient infiltration conditions and therefore are insufficient for estimating fracture permeability.…”