Comparative study of methods to estimate hydraulic parameters in the hydraulically undisturbed Opalinus Clay (Switzerland)

Abstract

International audienceThe deep borehole (DB) experiment gave the opportunity to acquire hydraulic parameters in a hydraulically undisturbed zone of the Opalinus Clay at the Mont Terri rock laboratory (Switzerland). Three methods were used to estimate hydraulic conductivity and specific storage values of the Opalinus Clay formation and its bounding formations through the 248 m deep borehole BDB-1: application of a Poiseuille-type law involving petrophysical measurements, spectral analysis of pressure time series and in situ hydraulic tests. The hydraulic conductivity range in the Opalinus Clay given by the first method is 2 × 10−14–6 × 10−13 m s−1 for a cementation factor ranging between 2 and 3. These results show low vertical variability whereas in situ hydraulic tests suggest higher values up to 7 × 10−12 m s−1. Core analysis provides economical estimates of the homogeneous matrix hydraulic properties but do not account for heterogeneities at larger scale such as potential tectonic conductive features. Specific storage values obtained by spectral analysis are consistent and in the order of 10−6 m−1, while formulations using phase shift and gain between pore pressure signals were found to be inappropriate to evaluate hydraulic conductivity in the Opalinus Clay. The values obtained are globally in good agreement with the ones obtained previously at the rock laboratory

Contrasting Mechanical and Hydraulic Properties of Wet and Dry Fault Zones in a Proposed Shale‐Hosted Nuclear Waste Repository

“…Values of k i, // and k f, // (10 −21 − 10 −20 ) are in the same range as values previously reported for nondeformed rock (Senger et al, 2018;Yu et al, 2017). Our data suggest a shear-enhanced fault-parallel permeability at slow sliding velocities (<1 μm/s) and at low σ′ n in agreement with previous tests on clay-rich samples (Wu et al, 2017;Zhang & Cox, 2000).…”

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“…In-situ derived hydraulic conductivities of the sandy facies come from f Lavanchy and Mettier (2012). The specific storage for the sandy facies are derived from g Yu et al (2017). The heat capacity for the shaly facies come from h Garitte et al (2014).…”

Safety-relevant hydrogeological properties of the claystone barrier of a Swiss radioactive waste repository: An evaluation using multiple lines of evidence

“…Values ≥ 10 -11 m/s may reflect relaxation of stresses around underground structures. Results from hydraulic tests in an inclined borehole crossing the entire Opalinus Clay (Yu et al 2017) show higher values (in the order of 10 -12 m/s) for the Opalinus Clay shaly facies than for its sandy facies (in the order of 10 -13 m/s), which is attributed to diagenetic cementation of the latter. Such a trend cannot be recognised in a compilation of previous tests (Jaeggi et al 2014; Fig.…”

“…Fig. 2) In the Opalinus Clay of the Mont Terri Rock Laboratory, which has a higher porosity compared with Benken due to lower maximum burial (see above), K tends to be somewhat higher and reaches values up to 7 10 -12 m/s (Jaeggi et al 2014;Yu et al 2017) (Fig. 2).…”

“…Data are available from three Nagra deep boreholes in Northern Switzerland (data compilation in Nagra 2010, Tab. A3-1), from numerous boreholes drilled in all directions in the Mont Terri Rock Laboratory (Jaeggi et al 2014;Yu et al 2017) and from shallow boreholes in the Swabian Romero and Gómez (2013) Alb in Germany (Hekel 1994). The hydraulic conductivity of the Opalinus Clay is depth-dependent (Fig.…”