Comparing flux‐averaged and resident concentration in a fractured bedrock using ground penetrating radar

Abstract

[1] Saline tracer transport experiments were performed to compare flux-averaged and resident concentration in a single subhorizontal fracture in sandstone bedrock. Tracer migration over a 14 m distance was monitored at an extraction well and imaged within the rock as it passed below a ground penetrating radar (GPR) positioned at the surface. Reflected radar amplitude was calibrated to tracer concentration by circulating saline fluid of known concentration through the fracture. Saline breakthrough curves measured at the well and within the rock were comparable but showed differences in both magnitude and shape. Transport differences were explored using flux-averaged and resident concentration first-passage-time models combined with streamline advective tracking. Application of the appropriate transport model to the two breakthrough curves produced identical estimates of dispersivity and similar estimates of effective fracture aperture. The tracer-derived fracture aperture also agreed reasonably well with hydraulic aperture derived from cross-hole pump tests. The availability of both flux and resident concentrations helped constrain the interpretation of the flow and transport behavior in the fracture. Flow appeared to be highly channelized with less than half the hydraulically swept area of the fracture contributing to efficient tracer transport.Citation: Becker, M. W., and G. P. Tsoflias (2010), Comparing flux-averaged and resident concentration in a fractured bedrock using ground penetrating radar, Water Resour. Res., 46, W09518,

The effect of spatial aperture variations on the thermal performance of discretely fractured geothermal reservoirs

“…The Altona reservoir represents a meso-scale field site, larger than a bench scale, artificial reservoir but smaller than a full sized geothermal reservoir. The Altona reservoir consists of Cambrian Potsdam Sandstone formation, where a five spot well system has been drilled in a 10 m by 10 m area, intersecting an isolated horizontal fracture 7.6 m deep (Becker and Tsoflias 2010). Ground penetrating radar has been used to determine the spatial aperture of the fracture (Tsoflias and Becker 2008), creating a reservoir with a characterized subsurface.…”

Inert and Adsorptive Tracer Tests for Field Measurement of Flow‐Wetted Surface Area

“…Since 2004, numerous Ground Penetrating Radar (GPR) surveys investigated the target fracture at the Altona site (Baker, 2014;Becker & Tsoflias, 2010;Perll, 2013;Talley et al, 2005;Tsoflias et al, 2015). One particular GPR survey of interest to this study imaged saline tracer flow paths between well 204 and 304 (Tsoflias et al, 2015).…”

Power law breakthrough curve tailing in a fracture: The role of advection

“…There is direct evidence that flow channeling occurs in bedrock fractures (Bourke, 1987;Moreno et al, 1985;Neretnieks, 1983Neretnieks, , 1987Neretnieks et al, 1982). In some cases, flow channeling has been imaged using ground penetrating radar (Becker and Tsoflias, 2010;Day-Lewis et al, 2006, 2003Talley et al, 2005). The similarity between flow channeling observed in cores (e.g.…”