Rock and porewater characterisation on drillcores from the Schlattingen borehole

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Report

Reference

Rock and porewater characterisation on drillcores from the Schlattingen borehole

WERSIN, P., et al. & NAGRA

Abstract

Radioactive waste in Switzerland is foreseen to be disposed in deep-seated low permeability sedimentary formations. Currently, the siting process is taking place within the so-called Sachplan procedure, in which Nagra has proposed six potential siting areas. One of these areas lies in the region "Zürich Nordost" where a large geological campaign within the project Opalinus Clay, a demonstration of feasibility (Entsorgungsnachweis), was carried out until 2002. In 2011, a deep borehole for geothermal purposes was drilled down to a depth of 1'508 m below surface (well head at 416.6 m above sea level) in Schlattingen (TG)1. It is located west of the village of Schlattingen, about 10 km NE of the Benken borehole, which was drilled within the feasibility demonstration study Entsorgungsnachweis. Nagra had the opportunity to accompany the borehole drilling in Schlattingen with an extensive investigation programme.

The scope thereof is to gain further information and understanding on the geology of the area, focussing in particular on the low permeability Jurassic sedimentary rocks. Thus, the section 731.5 – 988.9 m (Malm till [...]

WERSIN, P., et al. & NAGRA. Rock and porewater characterisation on drillcores from the Schlattingen borehole. Wettingen : NAGRA, 2013, 343 p.

Available at:

http://archive-ouverte.unige.ch/unige:101076

Disclaimer: layout of this document may differ from the published version.

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Arbeitsbericht NAB 12-54

Nationale Genossenschaft für die Lagerung radioaktiver Abfälle

Hardstrasse 73 CH-5430 Wettingen Telefon 056-437 11 11 www.nagra.ch

December 2013 P. Wersin, M. Mazurek, H.N. Waber, U.K. Mäder, Th. Gimmi, D. Rufer, A. de Haller

Rock and porewater characterisation on drillcores from the Schlattingen borehole

Institute of Geological Sciences, University of Bern With contributions from:

M. Adler, A. Bretscher, P. Alt-Epping (Uni Bern), C. Lerouge (BRGM), A.M. Fernández (CIEMAT), T. Al (University of New Brunswick), T. Oyama, K. Kiho (CRIEPI), Ch. Külls (University of Freiburg)

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KEYWORDS SGT-E2, Geothermiebohrung Schlattingen-1, SLA-1, geochemistry, mineralogy, isotopic composition, sampling, petrophysical methods, porewater, cation exchange properties, diffusion coefficients, organic matter, fluid inclusions

Arbeitsbericht NAB 12-54

Nationale Genossenschaft für die Lagerung radioaktiver Abfälle

Hardstrasse 73 CH-5430 Wettingen Telefon 056-437 11 11 www.nagra.ch

December 2013 P. Wersin, M. Mazurek, H.N. Waber, U.K. Mäder, Th. Gimmi, D. Rufer, A. de Haller

Rock and porewater characterisation on drillcores from the Schlattingen borehole

Institute of Geological Sciences, University of Bern With contributions from:

M. Adler, A. Bretscher, P. Alt-Epping (Uni Bern), C. Lerouge (BRGM), A.M. Fernández (CIEMAT), T. Al (University of New Brunswick), T. Oyama, K. Kiho (CRIEPI), Ch. Külls (University of Freiburg)

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Nagra.

All parts of this work are protected by copyright. Any utilisation outwith the remit of the copyright law is unlawful and liable to prosecution. This applies in particular to translations, storage and processing in electronic systems and programs, microfilms, reproductions, etc."

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7 References ... 201 Appendix A Sampling time sheets ... A-1 Appendix B Aqueous leachate data ... B-1 Appendix C pCO2 measurements ... C-1 Appendix D Diagenetic observations and carbonate mineral chemistry ... D-1 Appendix E Detailed petrographic description of veins ... E-1 Appendix F Fluid inclusion study ... F-1 Appendix G Preliminary modelling of squeezing experiments of Opalinus Clay ... G-1 G.1 Introduction ... G-3 G.2 Results ... G-5 G.2.1 Fitting the Cl profiles ... G-5 G.2.2 Implementing a simple calcite-only system ... G-7 G.2.3 Implementing complex chemistry and ion exchange reactions ... G-12 G.3 Conclusions ... G-19 Appendix H Recipe and preparation of a simplified artificial porewater for

Opalinus Clay and 'Brauner Dogger' ... H-1 H.1 Introduction and approach ... H-3 H.2 Modelling of the artificial porewater composition ... H-3 H.3 Recipe for the artificial porewater ... H-6 H.4 Preparation of the artificial porewater ... H-7

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List of Tables

Tab. 1-1: Compilation of laboratory tests and analysis for the Schlattingen borehole

carried out under the supervision of Uni Bern ... 2

Tab. 3-1: Sampling strategy for the mineralogical and geochemical studies in the Jurassic sediments. ... 9

Tab. 3-2: List of chemicals used for preparing the artificial porewater (APW). ... 30

Tab. 3-3: Recipe for preparing the artificial porewater (APW). ... 30

Tab. 3-4: Calculated composition of the artificial porewater (APW). ... 30

Tab. 3-5: Standing times and water masses squeezed during the feasibility experiment with sample SLA 878.45. ... 34

Tab. 3-6: Pressure steps and standing times for squeezing experiments. ... 35

Tab. 3-7: List of samples investigated by BRGM, their depth, the corresponding stratigraphy and the types of analyses. ... 38

Tab. 3-8: List of samples used for diffusion measurements and corresponding synthetic porewaters. ... 40

Tab. 3-9: X-Ray radiography data acquisition parameters for diffusion tests using the SkyScan 1072 MicroCT. ... 43

Tab. 3-10: Comparison of Dp values determined by radiography vs. through diffusion at PSI. ... 46

Tab. 4-1: Mineralogical analysis of the whole rock and clay-mineral fraction for standard samples. ... 50

Tab. 4-2: Mineralogical analysis of the whole rock and clay-mineral fraction for PSI samples. ... 52

Tab. 4-3: Relative proportions of clay minerals in the fraction < 2 µm obtained by ARQUANT for standard samples. ... 54

Tab. 4-4: Relative proportions of clay minerals in the fraction < 2 µm obtained by ARQUANT for PSI samples. ... 55

Tab. 4-5: Wet water content (by weight loss) for samples measured at Uni Bern and for samples measured at Ciemat (calculated from gravimetric dry water content, which is also listed). ... 60

Tab. 4-6: Grain, wet and bulk dry density measurements analysed at Uni Bern. ... 64

Tab. 4-7: Calculated water-loss and physical porosity, and S/L ratio for Uni Bern samples. ... 65

Tab. 4-8: Grain, bulk dry and bulk wet density measurements for samples analysed at Ciemat. ... 67

Tab. 4-9: Calculated water-loss and physical porosity for samples analysed at Ciemat. ... 68

Tab. 4-10: Porosity at maximum injection pressure (219 MPa, r > 3.3 nm) and macroporosity (r > 25 nm) obtained from Hg injection at Ciemat, and the corresponding fractions compared to the physical porosity obtained at Ciemat. ... 71

Tab. 4-11: N₂ BET data obtained at Uni Bern... 75

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Tab. 4-12: N2 BET data obtained at Ciemat. ... 76

Tab. 4-13: Total and internal surface areas for Ciemat samples. ... 77

Tab. 4-14: Water activity data. ... 82

Tab. 4-15: Average pore size (or water film thickness) of all pores and of external pores, and fraction of 'free' porewater estimated from geometrical considerations (see text). ... 85

Tab. 4-16: Solute concentrations of aqueous leachates, each analysis corresponds to average of 2 subsamples (see also Appendix B). ... 90

Tab. 4-17: Calculated pCO₂ and saturation indices for leachates (only shown for series a, Appendix B). ... 97

Tab. 4-18: Overview of water masses collected during squeezing. ... 101

Tab. 4-19: Water contents and grain density of samples subjected to squeezing. ... 102

Tab. 4-20: Chemical composition of waters squeezed at 200, 300, 400 and 500 MPa. ... 105

Tab. 4-21: Ratios of ion concentrations in waters squeezed at 500 MPa over those squeezed at 200 MPa. ... 107

Tab. 4-22: Calculated pCO₂ and saturation indices for all squeezed samples. ... 109

Tab. 4-23: Chemical composition of aqueous leachates of squeezed core materials. ... 114

Tab. 4-24: Grain density and chemical composition of aqueous leachates obtained from slices of squeezed cores SLA 780.66 (Parkinsoni-Württembergica Beds) and SLA937.89 (Opalinuston). ... 115

Tab. 4-25: Water and chloride inventories before after squeezing and Cl/H₂O ratios in (see text). ... 116

Tab. 4-26: Saturation indices and CO₂ partial pressures calculated for aqueous leachates of squeezed core materials. ... 117

Tab. 4-27: Stable isotopic composition of squeezed waters. ... 118

Tab. 4-28: Sample dimensions and measured and calculated physical properties for sample SLA 779.87. ... 119

Tab. 4-29: Chemical composition of sample aliquots from the advective-displacement experiment with sample SLA 779.87, including artificial porewater (APW). ... 123

Tab. 4-30: Results of PHREEQC simulations of sample aliquots from the advective- displacement experiment with sample SLA 779.87. ... 128

Tab. 4-31: Data of Ni-en extract solutions for selected standard samples (Uni Bern data). ... 132

Tab. 4-32: Data of Co-hexamine extract solutions, S/L = 1:20 (BRGM data)... 133

Tab. 4-33: ¹⁸O and ²H of porewater and wet water content (WC) derived from isotope mass balance for standard samples. ... 137

Tab. 4-34: Measurements of CO2, CH4, C2H6, C3H8 in the gas assuming that solid/gas equilibrium is attained. ... 141

Tab. 4-35: CO2/CO2 + alkanes ratios (expressed in %), C1/(C2 + C3) and C2/C3 and analytical errors calculated from measurements of gas concentrations in the total gas and expressed in %. ... 143

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Tab. 4-36: Carbon and oxygen isotopic composition of CO2 obtained on the ten gas cells using the gas bench technique, and carbon isotopic composition of

alkanes using gas chromatography coupled with IR-MS. ... 146

Tab. 4-37: Summary of samples studies for diagenetic analysis. ... 148

Tab. 4-38: Summary of the vein samples petrography. ... 155

Tab. 4-39: Isotope composition of rocks and vein minerals. ... 159

Tab. 4-40: Summary of experimental data of iodide diffusion tests with the radiography method. ... 160

Tab. 4-41: Measurements of sample swelling parallel to the core axis (= normal to bedding). ... 161

Tab. 4-42: Results of radiography and through-diffusion tests on samples of Opalinus Clay conducted at the University of New Brunswick. ... 162

Tab. 4-43: Summary of Rock-Eval and Leco analyses, together with calculated equivalent vitrinite reflectance values. ... 165

Tab. 4-44: Composition of drilling fluid and groundwater sample from the Wedelsandstein Formation (Albert et al. 2012), and estimated composition of groundwater unaffected by drilling fluid based on uranine and tritium mixing ratios. ... 166

Tab. 5-1: Cl^- inventory in samples subjected to squeezing and subsequent aqueous leaching. ... 168

Tab. 5-2: Mass balance for "excess sulphate" (see text). ... 177

Tab. 5-3: Comparison of measured and calculated parameters for S/L = 1 leachates (mol/l except pH). ... 179

Tab. 5-4: Comparison of measured and calculated parameters for S/L = 0.1 leachates (mol/l except pH). ... 179

Tab. 5-5: Derived Na/Ca ratios from cation occupancies on exchanger. ... 185

Tab. 5-6: Cation concentrations in porewater from squeezing and advective displacement data. ... 186

Tab. 5-7: pH, pCO2 and carbonate alkalinities estimated from different methods. ... 187

Tab. 5-8: Concentrations of minor anions derived from different methods. ... 188 Tab. A-1: Sampling time sheets. ... A-3 Tab. B-1: Parameters of leached samples. ... B-3 Tab. B-2: Saturation indices. ... B-11 Tab. D-1: Detailed petrography of the samples. ... D-3 Tab. D-2: Overview of the samples and measured carbonates therein. ... D-15 Tab. D-3: Biogenic carbonate measurements of samples 763.58, 799.12 and 833.69. ... D-16 Tab. D-5: Microprobe measurements of the Fe-calcite cement in samples 799.12

and 827.35. ... D-18 Tab. D-6: Fe-calcite composition in sample 833.69. ... D-19 Tab. D-7: Fe-calcite and Mg-calcite compositions in sample 886.90. ... D-20

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Tab. D-8: Measurements of dolomite and ankerite crystals in samples 763.58

and 827.35. ... D-21 Tab. D-9: Microprobe of the dolomite and ankerite crystals in samples 833.69

and 842.18. ... D-22 Tab. E-1: Detailed petrography of the vein samples... E-3 Tab. G-1: Species concentrations in mol/kg in the porewater from the four OPA

samples obtained at different squeezing pressures. ... G-4 Tab. G-2: The chemical system for calcite only simulations. ... G-7 Tab.G-3: Initial chemical condition for simulation with complex chemistry. ... G-13 Tab G-4: Composition of the exchange sites initially (200 MPa) and at the end

of the experiment (500 MPa). ... G-17 Tab. H-1: Modelled composition and other geochemical parameters of the APW

and the reference porewater for Opalinus Clay. ... H-5 Tab. H-2: List of chemicals suggested for the APW (Opalinus Clay / 'Brauner

Dogger'). ... H-6 Tab. H-3: Recipe for the APW (Opalinus Clay / 'Brauner Dogger'). ... H-6 Tab. H-4: Composition of the APW (Opalinus Clay / 'Brauner Dogger'). ... H-6

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List of Figures

Fig. 2-1: Geological map and main tectonic structures in Northern Switzerland (from Nagra NTB 08-04) and the location of the geothermal borehole at

Schlattingen. ... 5 Fig. 2-2: Geological profile of the Schlattingen borehole (Albert et al. 2012). ... 6 Fig. 2-3: Hydraulic conductivity data from hydrotesting in the Schlattingen borehole. ... 7 Fig. 3-1: Advective displacement apparatus, core preparation and electrochemical

cells. ... 28 Fig. 3-2: Rock squeezing apparatus at CRIEPI, (a) photo and (b) scheme. ... 31 Fig. 3-3: (a) Dry cutting of sample and (b) placement in sample chamber of the

squeezing apparatus. ... 32 Fig. 3-4: Feasibility experiment with sample SLA 878.45: Squeezing pressure (top)

and piston movement (bottom) as a function of time in days. Left: Sample

with axis normal to bedding; right: Sample with axis parallel to bedding. ... 35 Fig. 3-5: Diagram of the cell used for diffusion experiments by X-ray radiography. ... 42 Fig. 3-6: One-dimensional profiles of (a)  and (b) C/C₀ for sample SLA-857.8. ... 44 Fig. 3-7: Comparison of Dp values determined by radiography versus through

diffusion. ... 45 Fig. 4-1: Distribution of the three main mineral fractions for standard samples and PSI

samples (after Füchtbauer 1988). ... 49 Fig. 4-2: Distribution of the three main minerals fractions with depth for standard

samples. ... 53 Fig. 4-3: Example of model fits for clay-mineral quantification using ARQUANT

(sample SLA 929.40, Opalinus Clay). ... 56 Fig. 4-4: Contents of different clay-mineral species as a function of depth (standard

samples). ... 57 Fig. 4-5: Comparison of the relative contents of illite-smectite minerals in the < 2 µm

fraction based on the classic evaluation method and on ARQUANT. ... 57 Fig. 4-6: Comparison of the relative contents of kaolinite in the < 2 µm fraction based

on the classic evaluation method and on ARQUANT. ... 58 Fig. 4-7: Comparison of the relative contents of chlorite in the < 2 µm fraction based

on the classic evaluation method and on ARQUANT. ... 58 Fig. 4-8: Gravimetric wet water content vs. depth shown for Uni Bern samples. ... 61 Fig. 4-9: Gravimetric wet water content vs. clay-mineral content shown for Uni Bern

samples. ... 61 Fig. 4-10: Gravimetric wet water content vs. depth of the Ciemat samples, compared

with the data of the Uni Bern samples. ... 62 Fig. 4-11: Comparison of wet water contents of the Ciemat subsamples and of the Uni

Bern subsamples. ... 62 Fig. 4-12: (a) Water-loss porosity vs. depth and (b) water-loss porosity (closed

symbols) and physical porosity (open symbols) vs. depth. ... 66

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Fig. 4-13: Water-loss (WL) porosity vs. physical porosity; 1:1 line shown as

comparison. ... 66 Fig. 4-14: Comparison of depth profiles of bulk dry (in wet state) and grain densities

obtained for subsamples analysed at Ciemat and at Uni Bern. ... 68 Fig. 4-15: Correlations between the densities obtained at Ciemat and Uni Bern; (a) bulk

dry density (left), (b) grain density. ... 69 Fig. 4-16: Comparison of Ciemat and Uni Bern data; (a) WL porosity, (b) physical

porosity. ... 69 Fig. 4-17: Correlation between water-loss porosity and physical porosity of the Ciemat

samples; the Uni Bern data are also shown. ... 70 Fig. 4-18: Correlations between Ciemat and Uni Bern data; (a) WL porosity, (b)

physical porosity. ... 70 Fig. 4-19: Hg intrusion curves for samples analysed by Ciemat, grouped according to

the geological units (solid: intrusion, dashed: extrusion). ... 72 Fig. 4-20: (a) Depth profiles of the macroporosity (radius > 25 nm) and physical

porosity obtained by Ciemat; (b) Fraction of macropores (Hg macroporosity divided by physical porosity) and of Hg porosity (Hg porosity, r > 3.3 nm,

divided by physical porosity) versus depth... 72 Fig. 4-21: Fraction of Hg porosity (r > 3.3 nm) and of macroporosity (r > 25 nm) per

physical porosity plotted against the clay-mineral content. ... 73 Fig. 4-22: Full N₂ ad- and desorption isotherms measured for Schlattingen samples at

Uni Bern. ... 74 Fig. 4-23: BET specific surface areas versus physical porosity (left) and clay-mineral

content (right). ... 74 Fig. 4-24: Comparison of N2 ad- and desorption isotherms obtained for different

subsamples from the same core by Ciemat and Uni Bern. ... 76 Fig. 4-25: Profiles of specific surface areas; total surface areas from Ciemat (from data

at relative humidity of 0.75 and 0.85), N2 BET surface areas from Uni Bern

and (two samples) Ciemat. ... 77 Fig. 4-26: Correlations between total surfaca area (from relative humidity of 0.75) or

internal surface area (total minus N2 BET surface area) and the clay-mineral

content for the Ciemat samples. ... 78 Fig. 4-27: Measured water activities plotted as a function of depth below the surface... 79 Fig. 4-28: Measured water activities plotted (a) vs. the clay-mineral content and (b) vs.

the calcite content of the samples. ... 80 Fig. 4-29: (a) Water activities aw plotted against SBET surface area; (b) water activities

plotted against the apparent water saturation 'Sw', calculated as water-loss

porosity divided by physical porosity. ... 80 Fig. 4-30: (a) Water activities aw and apparent water saturations 'Sw' versus depth; (b)

water activities aw and clay-mineral content versus depth. ... 81 Fig. 4-31: Water adsorption isotherms obtained by Ciemat on powder samples with the

desiccator method, grouped according to the geological units. ... 83

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Fig. 4-32: Comparison of N2 isotherms (from Uni Bern and from Ciemat), water isotherms (Ciemat), and (shifted) Hg intrusion (Ciemat) of samples SLA 734.88 and SLA 880.30 in terms of adsorbed or intruded fluid volume per

sample mass as a function of pore radius. ... 85

Fig. 4-33: Comparison of pore size distributions for two samples (SLA 734.88 and SLA 880.30) derived from N₂ isotherms (BJH approach, Uni Bern and Ciemat samples), from the H₂O isotherm (Ciemat samples), and from the Hg intrusion (Ciemat samples). ... 86

Fig. 4-34: (a) Depth dependence of average pore radius (or average water film thickness) and of average radius of external pores when assuming one water layer in internal pores, both calculated from gravimetric water content and specific surface areas; (b) mineralogical composition of Ciemat samples, for comparison, as obtained on other subsamples at Uni Bern. ... 86

Fig. 4-35: (a) Mean pore radius against clay-mineral content, (b) mean radius of external pores against clay-mineral content. ... 87

Fig. 4-36: (a) Fraction of 'free' porewater estimated from water contents and surface areas against depth, (b) mineralogical composition of Ciemat samples, for comparison, as obtained at Uni Bern. ... 87

Fig. 4-37: Estimated fraction of 'free' porewater against clay-mineral content. ... 88

Fig. 4-38: Concentrations of various anions for leachates as a function of S/L ratio. ... 92

Fig. 4-39: Concentrations of varios cations for leachates as function of S/L ratio. ... 93

Fig. 4-40: (a) Sodium vs. chloride and (b) calcium vs. alkalinity for leachates at different S/L ratio. ... 93

Fig. 4-41: (a) pH vs. S/L ratio and (b) alkalinity vs. pH for leachates at different S/L ratios. ... 94

Fig. 4-42: Chloride concentrations of 1:1 leachates as a function of depth (a) in mg/l or mg/kgrock (b) in mg/l normalised to water-loss porosity... 95

Fig. 4-43: (a) Sulphate concentrations of 1:1 leachates in mg/l or mg/kgrock (b) SO4/Cl molar ratio, as a function of depth. ... 96

Fig. 4-44: (a) logpCO2 vs. S/L ratio and (b) SI(calcite) vs. S/L ratio. ... 99

Fig. 4-45: Calculated logpCO2 (bar) plotted for all 1:1 leachate samples. ... 99

Fig. 4-46: Water recovered by squeezing experiments as a function of depth and squeezing pressure. ... 103

Fig. 4-47: (a) Sample SLA 987.40 before and (b) after squeezing... 103

Fig. 4-48: Total water mass squeezed as a function of wet water content determined by drying at 105 °C to constant weight after squeezing. ... 104

Fig. 4-49: Evolution of ion concentrations in squeezed waters as a function of pressure for sample SLA 896.31 (Opalinus Clay). ... 107

Fig. 4-50: (a) Chloride and (b) sulphate concentrations vs. depth for squeezed waters at 200 MPa. ... 112

Fig. 4-51: Ion concentrations from aqueous leaching of samples SLA 780.66 (Parkinsoni-Württembergica Beds) and SLA 937.89 (Opalinus Clay). ... 113

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Fig. 4-52: Experimental conditions (pressures, temperature) during the porewater

displacement experiment, sample SLA 779.87. ... 120 Fig. 4-53: Hydraulic conductivity (K) derived from individual sampling intervals and

temperature, sample SLA 779.87. ... 121 Fig. 4-54: Electric conductivity (EC, EC-20: temperature-corrected) measured in-line

and variation of room temperature, experiment SLA 779.87. ... 122 Fig. 4-55: Plot of time intervals for each sample, experiment SLA 779.87. ... 122 Fig. 4-56: Chemical evolution of eluted samples for major components, plotted against

time expressed in pore volume fractions, experiment SLA 779.87. ... 124 Fig. 4-57: Chemical evolution of eluted samples for minor components, plotted against

time expressed in pore volume fractions, experiment SLA 779.87. ... 124 Fig. 4-58: Chemical evolution of eluted samples for anionic species, plotted against

time expressed in pore volume fraction, experiment SLA 779.87. ... 126 Fig. 4-59: Cation concentrations (meq/kg_rock) in Ni-extract vs. S/L ratio. ... 130 Fig. 4-60: Ni consumption as proxi for the cation exchange capacity (CEC) and sum of

cations in the Ni-en extract solutions (meq/kg_rock) versus depth, (a) for S/L = 0.1 and (b) S/L = 1. ... 131 Fig. 4-61: Co consumption as proxi of the cation exchange capacity and sum of cations

in Co-hexamine extract solutions at S/L of 1:20 (BRGM data) in meq/kg_rock. ... 134 Fig. 4-62: Cation occupancies (equivalent fractions in %) calculated from cation

concentrations in Co-extracts (BRGM data). ... 134 Fig. 4-63: Comparison between BRGM and Uni Bern data; (a) Ni or Co consumption

as proxi for cation exchange in meq/ kg_rock; (b) Na/Ca ratio (-) of extract

solutions. ... 136 Fig. 4-64: Wet water content by water-loss vs. wet water content from diffusive

exchange. ... 137 Fig. 4-65: Depth profiles of porewater (a) ²H and (b) ¹⁸O. ... 138 Fig. 4-66: ²H – ¹⁸O plot with measured porewater data (points) and GMWL (dotted

line). ... 139 Fig. 4-67: Evolution of the CO₂ partial pressure in each gas cell. ... 140 Fig. 4-68: Evolution of the CO₂ partial pressure in the ten gas cells during the solid/gas

equilibration time. ... 141 Fig 4-69: Evolution of the CO₂/(CO₂ + Alkanes) during the solid/gas equilibration

time. ... 143 Fig. 4-70: Evolution of the C1/(C2+C3) ratios during the solid/gas equilibration time. ... 144 Fig. 4-71: Evolution of the C2/C3 during the solid/gas equilibration time. ... 144 Fig. 4-72: δ¹³C and δ¹⁸O diagram showing isotopic compositions of outgassed CO₂ of

porewaters and calculated δ¹³C and δ¹⁸O of porewater and dissolved

bicarbonates of porewaters (same symbols as Fig. 4-67). ... 147 Fig. 4-73: Sample 833.69, Fe-calcite (blue); (a) continuous matrix between silty

components and biogenic fragments; (b) contact between Fe-calcite

cemented silt lens and uncemented silty claystone. ... 149

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Fig. 4-74: SLA 799.12 (a) The circular calcite/aragonite structure is a fossil wormhole, Fe-calcite is formed after pyrite; (b) Ba-Sr sulphate filling interstices

between Fe-calcite clusters. ... 149 Fig. 4-75: (a) SLA 763.58, accumulation of pyrite framboids, red arrows mark areas

where Fe-calcite has overgrown some tiny pyrite grains; (b) SLA 827.35, a

dolomite/ ankerite rhomb crystallizing around the pyrite framboid. ... 150 Fig. 4-76: (a) SLA 827.35, cementing dolomite/ankerite (bright blue), coloured thin

section; (b) SLA 763.58, zoned dolomite (core)/ankerite (rim) crystal clearly crystallised after the rhomboidal siderite. ... 151 Fig. 4-77: (a) SLA 763.58: Siderite crystals (bright grey) embedded in a Fe-calcite

matrix (Fe-cc), red arrows: hollow siderites, yellow arrows: Mg-rich

carbonates precipitated in the hollow siderites, BSE image; (b) SLA 833.69:

Siderite corona (polycrystalline) with an empty core filled with an ankerite

rhomb. ... 151 Fig. 4-78: (a) SLA 982.13: The largest Ba-Sr sulphate occurrence observed in the 6

studied samples. (b) SLA 827.35: Ba-Sr sulphate inter-grown with detrital

K-feldspar. ... 152 Fig. 4-79: (a) SLA 799.12: Partially replaced calcite/aragonite structures, the textures

of these SiO₂-replacements are typical for chalcedony, optical micrograph;

(b) SLA 827.35: Tiny diagenetic euhedral quartz grains forming a fine- grained matrix between detrital quartz grains, this fine-grained quartz

generally occurs together with diagenetic kaolinite. ... 153 Fig. 4-80: (a) SLA 827.35: Tiny kaolinite crystals (red arrows) are forming a matrix

between detrital quartz grains, BSE image; (b) SLA 827.35: Sheet- or needle-like crystals (red arrow, according to SEM-EDX analysis could be

illite), BSE image. ... 153 Fig. 4-81: δ¹⁸O (a) and δ¹³C (b) depth profile along borehole for whole rock carbonate

and vein calcite. ... 157 Fig. 4-82: (a) ⁸⁷Sr/⁸⁶Sr ratio depth profile for whole rock carbonate and vein calcite

(+celestite); (b) ⁸⁷Sr/⁸⁶Sr ratio of whole rock carbonate versus sheet silicate

content of the rock. ... 157 Fig. 4-83: (a) Sr content depth profile for whole rock carbonate and vein calcite

(celestite-bearing vein samples are not considered); (b) ⁸⁷Sr/⁸⁶Sr ratio of whole rock carbonate and vein calcite (upper) and sheet silicate content of the rock (lower) versus Sr content (normalized to calcite content for whole

rock samples). ... 158 Fig. 4-84: Tmax from Rock-Eval analysis as a function of depth. ... 163 Fig. 4-85: Representation of Rock-Eval pyrolysis data in a plot adapted from Espitalié

et al. (1984). ... 164 Fig. 5-1: Cumulative fractions of total Cl^- in solution and porewater released by

squeezing. ... 169 Fig. 5-2: Chloride profiles shown for 1:1 leachates (re-calculated to WL porosity),

squeezed water at 200 MPa, advective displacement experiment and

groundwater sample. ... 170

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Fig. 5-3: Anion-accessible fraction for chloride derived by comparsion of squeezing data at 200 MPa and re-calculated leaching data of near-by samples as

function of clay-mineral content. ... 171 Fig. 5-4: Chloride profile for two different assumptions with regard to anion-

accessible fraction. ... 172 Fig. 5-5: Profile of Cl^- concentration in pore and groundwaters from the Benken

borehole. ... 173 Fig. 5-6: Depth profiles for bromide from all available methods. ... 174 Fig. 5-7: Sulphate concentrations for squeezed waters, adevective displacement and

groundwater sample. ... 175 Fig. 5-8: Sulphate profile for squeezed water (200 MPa) in comparison with leachate

data re-calculated to porosity = 0.5  WL-porosity and advective

displacement data. ... 176 Fig. 5-9: (a) Depth profile of Na⁺ and (b) K⁺in squeezed, advectively displaced and

groundwater samples. ... 182 Fig. 5-10: Depth profile of (a) Ca²⁺and (b) Mg²⁺in squeezed and advectively displaced

samples. ... 183 Fig. 5-11: Depth profile of Sr²⁺ in squeezed and advectively displaced samples. ... 184 Fig. 5-12: ¹⁸O vs. ²H of squeezed waters, together with data derived from other

methods and data from the Benken borehole (from Nagra 2002). ... 190 Fig. 5-13: Depth profiles of (a) ¹⁸O and (b) ²H of porewater, based on all available

methods. ... 190 Fig. 5-14: Relationship between the evolutions of Cl- concentrations and of stable-

isotope compositions of water with increasing squeezing pressure. ... 191 Fig. 5-15: Profiles of δ¹⁸O and δ²H in pore and groundwaters from the Benken

borehole. ... 191 Fig. F-1: Sample areas cut out of SLA-10. ... F-4 Fig. F-2: Petrographic relations in sample SLA-10. ... F-4 Fig. F-3: Siderite in SLA-10. ... F-5 Fig. F-4: Early calcite in SLA-10 containing a liquid+vapour fluid inclusion of

weakly saline water (1.2 mass-% NaCleq.). ... F-5 Fig. F-5: Calcite in SLA-10. ... F-6 Fig. F-6: Siderite in SLA-10. ... F-6 Fig. F-7: Close-up of liquid + vapour inclusion in Fig. F-4 (same orientation of

image), prior to cooling or heating. ... F-8 Fig. F-8: Same fluid inclusion as in Fig. F-7 after cooling but prior to heating. ... F-8 Fig. F-9: Same fluid inclusion as in Fig. F-7 and F-8 after heating. ... F-9 Fig. F-10: Sample area cut out of SLA-11. ... F-10 Fig. F-11: Calcite in SLA-11. ... F-10 Fig. G-1: Pressure versus time relationship used in the model study. ... G-5

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Fig. G-2: Fitting computed to measured Cl profiles by injecting pure water. ... G-6 Fig. G-3: Measured and computed time series of pH and species concentrations. ... G-8 Fig. G-4: A phase transition from calcite to aragonite occurs at  300 MPa. ... G-9 Fig. G-5: Reducing the calcite dissolution rate to fit measured Ca concentrations. ... G-9 Fig. G-6: The volume fraction of calcite was reduced to 0.002 % so that calcite

is completely leached from the sample at about 350 MPa. ... G-10 Fig. G-7: Calcite reaction rate according to equation 1 and the reactive surface area

of calcite according to equation 2 over the course of the experiment. ... G-11 Fig. G-8: Time series of species and the pH for a calcite-only system. ... G-12 Fig. G-9: Compilation of all time series for the squeezed samples of the Opalinus Clay

(Tab. G-1). ... G-14 Fig. G-10: Only calcite and dolomite are primary minerals. ... G-15 Fig. G-11: Calcite, dolomite and gypsum are primary mineral phases. ... G-16 Fig. G-12: Mineral dissolution and precipitation reactions under close to equilibrium

conditions. ... G-16 Fig. G-13: The same scenario as that in Fig. G-11 but including ion exchange. ... G-17 Fig. G-14: The same scenario as in Fig. G-13 but with slower dissolution kinetics. ... G-18 Fig. G-15: Attempting a "best fit" of OPA sample SLA-878 45-I-SQ. ... G-19

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1 Introduction

Radioactive waste in Switzerland is foreseen to be disposed in deep-seated low permeability sedimentary formations. Currently, the siting process is taking place within the so-called Sach- plan procedure, in which Nagra has proposed six potential siting areas. One of these areas lies in the region "Zürich Nordost" where a large geological campaign within the project Opalinus Clay, a demonstration of feasibility (Entsorgungsnachweis), was carried out until 2002.

In 2011, a deep borehole for geothermal purposes was drilled down to a depth of 1'508 m below surface (well head at 416.6 m above sea level) in Schlattingen (TG)¹. It is located west of the village of Schlattingen, about 10 km NE of the Benken borehole, which was drilled within the feasibility demonstration study Entsorgungsnachweis. Nagra had the opportunity to accompany the borehole drilling in Schlattingen with an extensive investigation programme. The scope thereof is to gain further information and understanding on the geology of the area, focussing in particular on the low permeability Jurassic sedimentary rocks. Thus, the section 731.5 – 988.9 m (Malm till base Lias) as well as a deeper section in the Muschelkalk were cored and sampled for rock mechanical, geological and geochemical purposes. Geophysical logging was conducted for almost the entire borehole length (130 – 1'508 m depth). Hydrotesting was performed in a number of test intervals in the Jurassic, Triassic and Permian formations and in the underlying crystalline rock. Finally, primary stress measurements were conducted at selected depth levels.

The Rock-Water Interaction (RWI) group of University of Bern has participated in this investigation programme by on-site work (geological mapping and sampling of the drillcores, coordination and distribution of samples to different laboratories), as well as extensive laboratory studies. These were performed to a large extent in-house, but partly also contracted to other laboratories. The focus is on the sediments dominated by clay-rich lithologies from the Malm to the lower Lias, including the Effingen Member, the 'Brauner Dogger', the Opalinus Clay and the underlying Lias unit (also referred to as lower confining unit). The objectives are:

 to complement the mineralogical and geochemical database of the Jurassic rocks in Northern Switzerland,

 to improve the geochemical and hydrogeological process understanding of the porewaters of these rocks,

 to test and to improve new methods for characterising porewater chemistry.

The different tests and analyses are summarised in Tab. 1-1. Therein, it is indicated which of the data are documented in this report. The main scope of this report is to present:

 a comprehensive mineralogical dataset,

 a comprehensive petrophysical dataset (densities, porosities, surface areas),

 a comprehensive dataset on conservative porewater tracers (²H, ¹⁸O and Cl^-) and on anion- acessible porosity,

 additional data on porewater composition: cation concentrations, pH/pCO₂ conditions, cation exchange data,

 data on thermal maturity of organic matter,

 information on diagenetic processes and vein mineralisations, including isotope studies.

1 The present report refers to the first borehole in Schlattingen. Later the inclined borehole Schlattingen-2 was drilled.

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Tab. 1-1: Compilation of laboratory tests and analysis for the Schlattingen borehole carried out under the supervision of Uni Bern

Tests / analyses Laboratory this NAB

separate report Petrophysics

Water content, densities, porosities Uni Bern x

BET measurements Uni Bern x

Water content, densities, porosities Ciemat x

BET, Hg-porosimetry Ciemat x

Total surface area Ciemat

Water adsorption isotherms Ciemat x* x

Porewater /Cation exchange

Aqueous leaching Uni Bern x

Squeezing Criepi x

Advective displacement meas. Uni Bern x* x Water isotopes by diffusive exch. Uni Bern x

CEC, cation population Uni Bern x

CEC, cation population BRGM x

pCO2 & alkane measurements BRGM x Groundwater (1 sample) Hydroisotop x Rock characterisation, gases

Whole rock and clay mineralogy Uni Bern x

Mineral diagenesis Uni Bern x

Vein petrography Uni Bern x

Isotopes in carbonates and sulphates Uni Bern x

Fluid inclusions veins Uni Bern x

Noble gas analysis Uni Bern x

Thermal maturity Uni Bern x

Diffusion

Iodide diffusion by CT method Uni Brunswick x

Diffusion of He SCK.CEN x

* only part of data

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2 Geological setting

2.1 Geology Regional framework

The deep borehole at Schlattingen (SLA-1) is located in the border area of the Eastern Molasse basin about 10 km NE of the Benken borehole (Fig. 2-1). The NW-SE striking Neuhausen and Randen faults and the Hegau-Bodensee-Graben are the main bordering tectonic structures of this test area. The Tabular Jura borders the Molasse Basin from NE to SW. From there, Triassic and Jurassic sediments dip gently to the SE (3 – 5) under the Tertiary and Quarternary over- burden. The presence of Permian strata, which were not observed in the Benken borehole, had been previously proposed for the area east of the Neuhausen fault (Nagra 2008) and this was in fact confirmed by the Schlattingen borehole. The basement is made of highly metamorphic gneisses of Variscan age. The geological profile obtained from the borehole is depicted in Fig. 2-2.

Profile drilled in Schlattingen

The Quaternary sediments (0 – 53 m) are composed of unconsolidated sandy and partly clayey gravels. The underlying Molasse (53 – 489 m) can be separated into the Upper Marine Molasse (OMM), composed of rather homogeneous calcareous sandstones and some siltstones, and the Lower Freshwater Molasse (USM), silty to sandy marls interbedded with silty claystones, fine- grained sandstones and thick sandstone beds. The bottom of the Tertiary (489 – 491 m) is made of a thin bed of reddish claystone – the Eocene Boluston.

The underlying Malm unit (491 – 758 m) is made of mainly micritic, sometimes massive limestones with variable contents of sand, silt and clay down to a depth of about 733 m. The lower- most Malm unit consists of the silty to sandy calcareous marls of the Effingen Member and the Birmenstorf Member.

The underlying rocks of Dogger age are generally rich in clay minerals and can be separated into the 'Brauner Dogger' unit (758 – 831m) and the underlying Opalinus Clay (831 – 950 m).

The upper part of the 'Brauner Dogger' sediments with a thickness of about 50 m displays a rather variable lithology, but a tendency of increasing clay-mineral content with depth. The uppermost beds (Wutach Formation) and also some of the underlying sediments (Parkinsoni- Württembergica Beds, Humphriesioolith Formation) contain variable amounts of iron oolithes, which represent periods of slow deposition or non-deposition. The underlying about 27 m thick Wedelsandstein Formation is composed of claystones and argillaceous marls with silty- calcareous beds.

The about 120 m thick Opalinus Clay² is characterised by fairly homogeneous silty to fine sandy claystones with silty lenses and siderite concretions.

The about 53 m thick Liassic rocks (950 – 1'003 m) are also generally rather rich in clay- mineral content. They are made of variable sequences of marls, claystones and limestones.

2 Note that uppermost parts have been termed "Achdorf Formation" previously.

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The Keuper unit (1'003 – 1'112 m) consists of a 44 m thick, fairly clay-rich, heterogeneous sequence with dolomitic and anhydritic beds in the upper part, followed by 65 m of the homogeneous dolomitic claystone and marl beds of the Gipskeuper containing anhydrite nodules and layers. The Muschelkalk unit (1'112 – 1'251 m) consists in the upper part of a dolomitic sequence (Trigonodus-Dolomit) underlain by a limestone sequence (Hauptmuschel- kalk), both containing open fractures. The middle sequence consists of inhomogeneous beds of dolomites, claystones and marls with some anhydrite and a specific evaporitic layer (1'209 – 1'214 m) of halite with anhydrite. The lowest Muschelkalk sequence is made of claystones and marls underlain by calcareous sediments. The Buntsandstein (1'251 – 1'351 m) consists of sandstones, which are partly clayey, partly calcareous.

The Permian Rotliegendes rocks (1'261 – 1'335 m) consist of brownish-red clayey siltstones, silty claystones as well as coarse-grained sandstones. They contain breccia of clay-rich material and gneiss.

The underlying crystalline rock was drilled down to a final depth of 1'508 m. It is composed of high-grade metamorphic gneisses and basic intercalations.

2.2 Hydrogeological conditions

The near-by river Rhine poses an important constraint on groundwater flow conditions in the Quaternary, Tertiary and to some degree also in the Malm units.

Hydrotests were performed in the borehole below the Tertiary sediments (Beauheim 2013, Reinhardt et al. 2013a and b, Reinhardt & Rösli 2013a and b). The measured hydraulic heads and hydraulic conductivities indicate significant variations and rather large uncertainties. The measured head values ( 400 m asl) in the top Malm sediments are similar to those in the lowest crystalline rocks suggesting subhydrostatic conditions. The tests in the 'Brauner Dogger', the Muschelkalk and the Permian show head values higher than the surface level, suggesting artesian conditions.³

The results from hydrotesting are depicted in Fig. 2-3. The measured hydraulic conductivities are highest in the Buntsandstein ( 10^-6 m/s). In the Muschelkalk section, values are in the range of about 10^-8 to 10^-9 m/s. Lower values were observed in the three intervals from the 'Brauner Dogger' unit. The section in the Wedelsandstein Formation yielded the highest value thereof ( 10^-9 m/s), here water flow into the borehole was observed (groundwater could be sampled, see section 4.14). The section in the top Malm displays values in the range of 10^-10 m/s, which explains the absence of water noted in the borehole.

3 Opalinus Clay was not tested due to problems with borehole stability.

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Fig. 2-1: Geological map and main tectonic structures in Northern Switzerland (from Nagra 2008) and the location of the geothermal borehole at Schlattingen.

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Fig. 2-2: Geological profile of the Schlattingen borehole (Albert et al. 2012).

Recently, the Malm lithostratigraphic terminology has been revised: Plattenkalk =>

Bankkalke; Massenkalk/Quaderkalk => Felsenkalke/Massenkalk; Mittl. Malmmergel =>

Schwarzbach-Fm.; Wohlgeschichtete Kalke => Küssaburg-Sch. bis Wangental-Sch.

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Fig. 2-3: Hydraulic conductivity data from hydrotesting in the Schlattingen borehole.

Figure from B. Frieg, 26.4.2013 based on Reinhardt et al. (2013a and b) and Reinhardt &

Rösli (2013 a and b).

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3 Sampling and methods

3.1 Sampling 3.1.1 Sampling strategy

The basis for the planning of the sampling programme was the predicted stratigraphic sequence.

It was assumed that, in the ideal case, core materials would be available between the top of the Effingen Member (Malm) and the top of the Trigonodus-Dolomit aquifer (upper Muschelkalk).

The thickness of this core sequence was estimated at almost 400 m. Of these, 263.9 m were actually cored (core diameter 10 cm), and the sampling programme was adjusted accordingly.

The target was to take a standard sample about every 5 m along core. In detail, the sampling strategy is summarised in Tab. 3-1 and sample conditioning protocols are given in section 3.1.2.

Tab. 3-1: Sampling strategy for the mineralogical and geochemical studies in the Jurassic sediments.

Purpose Number

of samples Sampled lithologies Approximate sample length

[cm]

Standard samples [PW] 53 No lithological bias 25 Samples for dissolved noble and

reactive gases [NG/NG+] 31 Always close to standard

samples 15

Samples for porewater squeezing

[SQ] 12 Focused on samples rich in

clay minerals 15

Samples for advective

displacement of porewater [AD] 4

Focus in lithologies rich in clay minerals. 2 samples from

the 'Brauner Dogger', 2 from Opalinuston

15 Samples for diffusion studies at

PSI [PSI] 10 Coverage of all lithologies 12

Samples for diffusion studies at University of New Brunswick

[UNB] 17 Coverage of all lithologies 10

Samples for diffusion studies at

SCK•CEN [SCK] 2 Opalinuston 15

Samples for cation-exchange

experiments at BRGM [CEC] 19 Coverage of all lithologies 4-7 Samples for CO2 contents in

porewater [CO2] 9 Coverage of all lithologies 20 – 25 Samples for out-diffusion

experiments [DE] 6 Coverage of all lithologies 20 Samples for specific petrophysical

parameters at Ciemat 14 Coverage of all lithologies 5 – 10*

* in all but one case a subsample of a standard sample

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Standard samples were taken approximately every 5 m along core. From the 53 standard samples 30 were processed for subsequent analyses, the remaining ones were kept as backup material. These samples were packed on-site according to the standard procedure (see section 3.1.2). This dense sampling required the presence of RWI staff at all times during core drilling. The standard programme included analyses pertaining to the following parameters:

 Whole-rock mineralogical composition

 Mineralogical composition of the clay fraction (< 2 µm)

 Bulk wet, bulk dry and grain density

 Gravimetric wet water content

 Chemical composition of aqueous extracts

 Diffusive isotope exchange (stable-isotopic composition of porewater)

 BET surface area

 Water activity

The emphasis of the standard samples was to provide coverage of the whole profile at largely even spacing between samples with a higher frequency towards the expected aquifers. It was also attempted to study all lithologies and to avoid a sampling bias towards specific rock types.

It was planned to take standard samples and those for other methods as presented below in a co- ordinated way, ideally using adjacent, lithologically similar core materials for all applications.

Given the lithological heterogeneity and natural or induced fracturing of the core materials, such full co-ordination was not always possible. Therefore, some deviation from a strictly even 5 m spacing had to be accepted or, alternatively, samples for different applications were taken from lithologically similar but not directly adjacent core materials:

 Samples for the study of dissolved noble and reactive gases were taken approximately every 10 m, in close vicinity to the standard samples where feasible (more than half the samples lie within 1 m of a standard sample). In all cases, the samples were selected in such a way that the lithology was as close as possible to that of the nearest standard sample. Moreover, samples had to be free of macroscopic fractures. A total of 31 samples were taken.

 14 samples for porewater squeezing were taken along the whole core profile. In order to maximise the water content (and therefore the success of the squeezing yield), the focus was on samples rich in clay minerals. Due to this criterion, it was not always possible to spatially associate these samples to the standard samples. For advective-displacement experiments, two samples from the 'Brauner Dogger' and two from Opalinus Clay were taken.

 Ten samples for diffusion studies at PSI were taken from the 'Brauner Dogger', thereof 4 clay-rich and 2 calcareous, clay-poor samples. Further, 2 samples each were taken from Opalinus Clay and from the Lias. For diffusion studies at the University of New Brunswick, 17 samples, covering the entire profile from Effingen Member to Lias, were taken. In total 3 samples (1 from Effingen Member, 2 from 'Brauner Dogger') were calcareous, the rest was rich in clay minerals.

 For the diffusion studies at SCK•CEN, two samples from Opalinus Clay were taken.

 In total 19 samples were taken for cation-exchange experiments at BRGM. They covered the whole cored profile and all major lithologies.

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 For the study of CO2 contents in porewater at BRGM, 9 samples were taken, where possible in close proximity of the samples taken for cation-exchange experiments.

 Six samples were taken for out-diffusion experiments. Because of time constraints, it was later decided not to conduct these experiments.

 A subset of 14 out of 30 standard samples was used to obtain water adsorption isotherms, total surface areas by the isotherms, total surface areas, and pore-size method, and pore-size spectra by mercury porosimetry at Ciemat. The strategy was to preferably choose samples located close to samples on which the cation exchange capacity was determined, or which were used for squeezing or for diffusion measurement at PSI and UNB. This resulted in two samples from Effingen Member, one each from Variansmergel Formation, Parkinsoni- Württembergica Beds, Wedelsandstein Formation, Obtusus Beds, and Psiloceras Beds, and 7 from Opalinus Clay. The subsamples SLA 734.88, SLA 742.48, SLA 765.31, SLA 816.73, and SLA 833.08 were prepared some time after the preparation of the correspond- ding porewater (PW) subsamples, all other samples were prepared at the same time (except for SLA 780.35, where no porewater subsample was taken).

3.1.2 Sampling procedures On-site sampling: general considerations

The preservation of the in-situ water saturated state of the rock material after drillcore extraction and during subsequent sampling is of paramount importance for porewater and dissolved gas characterisation of such samples. Any extended exposure to extrinsic fluids (such as surface water used for core cleaning) or gases (primarily air) will result in changes of the original state and cause potential contamination.

As dry-cleaning of the drillcore was not feasible due to the employed viscid drilling fluid, it was cleaned with groundwater available on-site while limiting both the amount of water and the duration of cleaning to a necessary minimum. Concurrent to manual drying and the subsequent metrical and geological surveying of the core by the on-site geologist of SJ Geotec AG, potential sections of the core were marked and photographically documented for sampling according to the sample requirements given by the sampling programme. Doing so allowed for their immediate processing as soon as these sections were cleared for sampling by the on-site geologist. Sample sections were retrieved as full cores (¹/1) as quickly as possible, with the aim of protecting them from atmospheric exposure. Existing bedding-parallel breaks in the core, caused by disking were used wherever possible; otherwise samples were trimmed by dry cutting on a rock saw. When multiple samples had to be processed from the same core, they were initially preserved in evacuated plastic bags by temporary vacuum sealing using a rapid house- hold vacuum cleaner. This allowed for prioritizing further processing of samples with more stringent timing constraints (e.g. samples for noble-gas studies) without compromising others.

On average, samples were in an initial protected condition after less than 20 min (Appendix A).

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On-site sampling: procedures for porewater chemistry (sample types: PW, AD, DE, PSI, UNB, SKC, SQ)

Unless specifically requested by the sampling programme (e.g. calcareous or sandy sections within a predominantly marly to silty lithology), samples were selected to represent a homogeneous section of the lithology represented by the host core section and to not interfere with stratigraphic boundaries.

Without removing it from its temporary vacuum bag (if it was in one) the sample was put into a plastic coated thick Al-bag, which was evacuated and heat sealed. Unlike the other sample types, SQ samples required the addition of O2 absorbers and O2 indicator tablets, which were provided by CRIEPI. The absorbers and tablets were spatially dispersed over the sample surface and already added during temporary sealing where applicable. All samples were additionally sealed inside a robust plastic bag for mechanical protection of the Al-bag which acts as the main gas barrier.

On-site, samples were stored cool with the aid of commercially available cooling boxes and coolant bricks until they could be transported to the laboratory at Uni Bern, where they were stored at 4 °C in a cooling room. Transports were made based on the number of acquired samples, with the running average transport frequency ranging between weekly to once every fortnight.

On-site sampling: procedures for porewater noble and reactive gas composition and for CEC samples measured by BRGM

Trimming of central sections and conditioning of CEC samples:

Where applicable, porewater gas composition samples were taken close to porewater chemistry samples and according to the same field criteria (section above). Immediately after removal from the core or the temporary storage bag, the sampled core section was trimmed by dry cutting to a square shaped central section in order to remove the partly degassed and drill-fluid / cleaning water contaminated rim of the core. Central section dimensions are about⁴ 45 × 45  70 mm and 60  60  250 mm for porewater noble and reactive gas samples (label:

NG, NG+) and CO₂ content samples (label: CO2), respectively, with the largest dimension being parallel to the core axis. Accordingly, the corresponding thickness of the removed rim is between about 27 to 18 mm (NG/NG+) and 20 to 7 mm (CO₂) with the larger value pertaining to the thickness perpendicular to the side-face of the central section and the smaller one measured along the latter's angle bisector. All cut surfaces were brushed off to remove rock powder created by the sawing process.

Where CEC samples were taken, this was always done together with either a NG/NG+ or CO2 sample from the same central section. For these CEC samples, an approximately 5 mm thick slab was cut away from the trimmed central section, parallel to the core axis (with the rest of the material subsequently being used as noble- or reactive gas sample). These slabs were subsequently manually crushed with a hammer into pieces on a cm scale in order to fit into perforated plastic coated Al-pouches which were then immediately submerged in N2(liq.) in a Dewar vessel, where they remained at -196 °C until handed over to BRGM.

4 Variations up to approximately  5 mm are possible. The given values are setpoint values; no verification was performed.

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Conditioning of NG and NG+ samples:

Immediately after trimming, the wet weight of the central section was recorded and the block then sealed in a high vacuum container. The lids of these stainless steel containers are fitted with a 30 cm or 1 m Cu tube (for the NG and NG+ samples, respectively) and can be connected to the containers by a ConFlat-type (copper gasket and knife edge) flange with a Cu seal. As soon as the container was screwed shut finger-tight, evacuation of the atmospheric gases contained within was started using a pump connected to the Cu tube, simultaneously to final tightening of the CF seal in order to minimise porewater gas contamination by air. Upon sealing of the CF flange and pressure drop rates starting to level off (indicating conditions approaching a state where concurrent sample degassing begins⁵), the sample was subjected to cyclic pressure rinsing using commercially available Kr (99.99 % purity) before it was vacuum-sealed by crimping the Cu tube with a screw-driven steel clamp during final pumping.

For the NG+ samples, a total of 8 crimpings were made as a time series, resulting in 8 gas aliquots representing the composition of the degassed porewater gases after 0.5, 2.50, 9.00, 33.00, 53.00, 104.00 and 241.00 hours.

The time markers, durations and recorded pressures of all these steps were recorded for quality control of the ensuing gas analyses (Appendix A). The average timespan between the start of sawing and the beginning of the first Kr flushing (after which contamination of the central section by atmospheric gas is severely reduced) is 8.2  2.5 (1  s.d.) minutes. The final pressure in the containers varies between 1.80 and 4.40 mbar and is dependent on the H₂O content and degassing properties of the rock material.

Conditioning of CO₂ samples:

This followed the same general procedure as for the NG/NG+ samples, with some deviations regarding the equipment. The sample containers supplied by BRGM were sealed by means of a rubber ring seal and had built-in pressure gauges with a 10 mbar resolution. Due to the latter, the pumping thresholds were at 10 or 20 mbar. Commercially available He (99.0 % purity) was used as a flushing gas and after the final pumping step a final He pressure in the range of 700 mbar was applied to the containers before they were sealed by closing the two ball valves connecting them to the pump and the He reservoir.

As for the NG/NG+ samples, the time markers, durations and recorded pressures of all steps were recorded for quality controls of the ensuing gas analyses (Appendix A). The average timespan between start of sawing and beginning of the first He flushing (after which contamination of the central section by atmospheric gas is severely reduced) is 10.6  1.8 (1  s.d.) minutes.

3.1.3 Sample types presented in this report

Samples extracted from drillcores were used for a variety of methods. For consistency reasons, all samples are designated in the same fashion in the following by adding the average depth to

"SLA", for example "SLA 787.33".

5 Initial gas "production" from the sample is most likely caused by vacuum drying of the wet surface, with the bulk of this gas volume being H2O(vap.).

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From each sampled core, subsamples were taken for different analytical methods. The data presented here includes the following sample types used for the following methods (see also Tab. 3-1):

 Standard samples: These are samples referred to in Appendix A by "SLA-787.33-PW" etc.

and have also been designated as SLA-1, SLA-2 etc. Subsamples were taken for mineralogical analysis, determination of petrophysical parameters (Uni Bern and Ciemat), aqueous extraction analysis, CEC determination (Uni Bern for some selected samples), and

18O and ²H in porewaters.

 Samples for diffusion studies at PSI: These are samples referred to in Appendix A by "SLA- 789.27-PSI" etc. They were selected for diffusion studies at PSI (not presented in this report). Five of these were studied for mineralogical composition and gravimetric water contents.

 Samples for porewater squeezing: These are samples referred to in Appendix A by "SLA- 780.66-SQ" etc.

 Sample for advective displacement: This regards one sample referred to in Appendix A by

"SLA-779.87-AD".

 Samples for CEC: These are samples which were analysed by BRGM for cation exchange parameters. They are referred to in Appendix A by "SLA-742.11-CEC" etc. Note that additional CEC data were generated by Uni Bern on standard samples.

 Samples for CO₂ in porewater: These are samples analysed by BRGM. They are referred to in Appendix A by "SLA-742.11-CO2" etc.

 Samples for isotope composition in rocks and veins: Most of these were taken from the standard samples. In addition selected samples from overlying and underlying sediment rocks were analysed.

 Samples for diagenetic analysis: These were extracted from selected sediment layers.

 Samples for diffusion studies at the University of Brunswick: These are core samples referred to in Appendix A by "SLA-857.85-UNB" etc.

3.2 Petrophysical methods

3.2.1 Gravimetric wet water content and water-loss porosity

The gravimetric wet water content (defined below) of the preserved core samples was obtained by gravimetric determination of water loss. Gravimetric water-loss was measured by drying sample aliquots of between 140 to 220 g at 105 °C to constant weight. Four measurements were performed for all samples. The gravimetric wet water content (ww) was then calculated according to:

% 100

%

100  

 



w pw w

r w w

m m m

m

w m (3-1)

where m_w is the wet mass of rock, m_r is the mass of dry rock of the sample, and m_pw is the mass of porewater.

Rock and porewater characterisation on drillcores from the Schlattingen borehole

Report

Reference

Rock and porewater characterisation on drillcores from the Schlattingen borehole

Arbeitsbericht NAB 12-54

December 2013 P. Wersin, M. Mazurek, H.N. Waber, U.K. Mäder, Th. Gimmi, D. Rufer, A. de Haller

Rock and porewater characterisation on drillcores from the Schlattingen borehole

Arbeitsbericht NAB 12-54

December 2013 P. Wersin, M. Mazurek, H.N. Waber, U.K. Mäder, Th. Gimmi, D. Rufer, A. de Haller

Rock and porewater characterisation on drillcores from the Schlattingen borehole

Table of Contents

List of Tables

List of Figures

1 Introduction

2 Geological setting

2.1 Geology Regional framework

Profile drilled in Schlattingen

2.2 Hydrogeological conditions

3 Sampling and methods

3.1 Sampling 3.1.1 Sampling strategy

3.1.2 Sampling procedures On-site sampling: general considerations

On-site sampling: procedures for porewater chemistry (sample types: PW, AD, DE, PSI, UNB, SKC, SQ)

On-site sampling: procedures for porewater noble and reactive gas composition and for CEC samples measured by BRGM

3.1.3 Sample types presented in this report

3.2 Petrophysical methods

3.2.1 Gravimetric wet water content and water-loss porosity