29 Jun 2022
29 Jun 2022
Status: a revised version of this preprint was accepted for the journal HESS.

Characterization of the highly fractured zone at the Grimsel test site based on hydraulic tomography

Lisa Maria Ringel1, Mohammadreza Jalali2, and Peter Bayer1 Lisa Maria Ringel et al.
  • 1Applied Geology, Institute of Geosciences and Geography, MLU Halle-Wittenberg, Halle, Germany
  • 2Department of Engineering Geology and Hydrogeology, RWTH Aachen, Aachen, Germany

Abstract. In this study, we infer the structural and hydraulic properties of the highly fractured zone at the Grimsel test site in Switzerland by a stochastic inversion method. The fractured rock is modeled directly as a discrete fracture network (DFN) within an impermeable rock matrix. Cross-hole transient pressure signals recorded from constant rate injection tests in different intervals provide the basis for the herein presented first field application of the inversion. The experimental setup is realized by a multi-packer system. The geological mapping of the structures intercepted by boreholes and data from previous studies that were undertaken as part of the in-situ stimulation and circulation (ISC) experiments facilitate the setup of the site-dependent conceptual and forward model. The inversion results show that two preferential flow paths between the two boreholes can be distinguished. One is dominated by fractures with large hydraulic apertures while the other path consists mainly of fractures with a smaller aperture. The probability of fractures linking both flow paths increases the closer we are at the second injection borehole. The results accord with the findings from other studies conducted at the site during the ISC measurement campaign and add new insights about the highly fractured zone at the prominent study site.

Lisa Maria Ringel et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2022-209', Anonymous Referee #1, 22 Aug 2022
    • AC1: 'Reply on RC1', Lisa Maria Ringel, 08 Nov 2022
  • RC2: 'Comment on hess-2022-209', Anonymous Referee #2, 12 Oct 2022
    • AC2: 'Reply on RC2', Lisa Maria Ringel, 08 Nov 2022
    • AC3: 'Correction to our Reply on RC2', Lisa Maria Ringel, 22 Nov 2022

Lisa Maria Ringel et al.

Lisa Maria Ringel et al.


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Short summary
Fractured rocks host a class of aquifers that serve as major freshwater resources worldwide. This work is dedicated to resolving the three-dimensional hydraulic and structural properties of fractured rock. For this purpose, hydraulic tomography experiments at the Grimsel test site in Switzerland are utilized and the discrete fracture network is inverted. Comparison of the inversion results with independent findings from other studies demonstrate the validity of the approach.