| Understanding in-situ fluid flow pathways in deformed rock is a fundamental aspect of the economic development of siliciclastic petroleum reservoirs and groundwater aquifers. The limited spatial resolution of remote sensing instruments, and the relative transparency of subsurface fluids to those instruments, makes it difficult to document fluid flow processes in-situ. I have studied an ancient, chemically reactive flow system, now exposed in outcrop, where the spatial distribution of mineralization implies paleo flow pathways. Numerical simulations complement field characterization by quantitatively evaluating the sensitivity of flow pathways to the hydraulic and geometric attributes of outcrop-scale structures.; The Aztec Sandstone at the Valley of Fire State Park, Nevada, is a reservoir and aquifer analog characterized by a complex hierarchy of deformation bands, joints and faults. During deformation, diagenetic processes produced alteration assemblages whose distribution is influenced by structural heterogeneities. Metasomatic reaction fronts refract where they intersect deformation bands. Analytical and numerical modeling of this refraction indicates that band permeability is reduced by 1.3 to 2.3 orders of magnitude.; Alteration fronts also are perturbed by joints. Numerical simulations indicate that, in addition to joint geometry, the ratio of effective joint permeability to matrix permeability determines whether flow utilizes connected joint networks or indirect pathways through the porous matrix. Comparing the outcrop distribution of alteration with simulations indicates that effective joint permeability is 5 orders of magnitude greater than matrix permeability.; Proper formulation of effective joint permeability yields a mathematically consistent hydraulic continuum from joints to deformation bands, providing a unifying approach to problems of fluid flow through fractured rock. In contrast, faults are hydraulically complex and may be classified as barriers, conduits, barrier-conduits, or conduit-barriers. The hydraulic behavior of conduits depends strongly on fault width while the hydraulic behavior of barriers depends largely on fault permeability. |
