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High temperature compaction of hot-pressed Rochester shale powder

High temperature compaction of hot-pressed Rochester shale powder. Rolf Bruijn , D. Mainprice & L. Burlini. Thanks to: S. Misra; K. Kunze, M. Pistone, E. Tumarkina and E. Moulas. Deformation studies involving phyllosilicates. (Semi)-brittle regime Lowered friction coefficient

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High temperature compaction of hot-pressed Rochester shale powder

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  1. High temperature compaction of hot-pressed Rochester shale powder Rolf Bruijn, D. Mainprice & L. Burlini Thanks to: S. Misra; K. Kunze, M. Pistone, E. Tumarkina and E. Moulas D-ERDW Geological Institute

  2. Deformation studies involving phyllosilicates • (Semi)-brittle regime • Lowered friction coefficient • Low permeability  high Ppore • Low stress mica kinking • Plastic regime • Low shear stress for basal-plane slip • Switch to low stress dislocation creep • Enhanced diffusion creep upon foliation development Studies limited to T <400 ºC, avoided dehydration and/or focussed on mono-phase material Need for studies on T >400 ºC deformation of poly-phase phyllosilicate-rich material Natural samples Hot-pressed synthetic powder Hot-pressed natural powder D-ERDW Geological Institute

  3. Sample selection • Natural samples • Realistic, but complex composition • High sample-to-sample variability • Fractured / weathered / low integrity • Hot-pressed synthetic powder • Simplified and unrealistic composition • More homogeneous fabric and composition • Intact material • High-porosity starting material • Complex composition • Detailed dehydration study • Phase stability modelling • Hot-pressed natural powder • Realistic, but complex composition • More homogeneous fabric and composition • Intact material • High-porosity starting material • High porosity • Initial sample compaction • Delayed plastic deformation This talk: High T/low-strain deformation behaviour of porous hot-pressed natural shale powder D-ERDW Geological Institute

  4. Starting material • Rochester Shale • Location: Western New York State • Unit: Upper Clinton Group (Silurian) • Composition: Clay/Mica (60-75 vol.%) (C/M) Quartz (20-30 vol.%) Oxides (2-4 vol.%) Other (2-5 vol.%) • Sample preparation • 1. Rock crushing + sieving (d <150 µm) • 2. Uniaxial cold press (200 MPa) • 3. Hot Isostatic Press (160 MPa, 590 ºC for 24 hrs) • New sample properties • Connected porosity: 12.5 ± 1.2 % • Water content: 2.56 ± 0.02 wt.% D-ERDW Geological Institute

  5. Methodology • Uniaxial compression tests • s1 > s2 = s3 • T: 500, 650 & 700 ºC at 300 MPa • Strain rate: 10-3 – 10-6 s-1 • Sample dimensions • Diameter: 10-15 mm • Length: 6-22 mm • Assembly: Fe- or Cu-jacket  water loss • Analysis • Porosity:Helium-pycnometer • Strain: new sample dimensions • KFT: water content • XRD: New mineral phases • SEM: Mineral phases and fabric D-ERDW Geological Institute

  6. Mechanical behaviour D-ERDW Geological Institute

  7. Deformation behaviour D-ERDW Geological Institute

  8. Mica dehydration / system water loss • Perple-X model • Composition determined by XRF • Loss of ignition = 2.7 wt.% • Enhanced mica-dehydration between 650 and 700 ºC • Partial melting from 710 ºC • Fields stable for H2O > 1.0 wt.% • System water loss • Source: mica-dehydration • Sink: Assembly jacket • Initial H2O = 2.7 ± 0.2 wt.% • Temperature dependent • Compaction rate dependent D-ERDW Geological Institute

  9. Conclusions This talk: High T/low-strain deformation behaviour of porous hot-pressed natural shale powder • At all temperatures: Very high strength, without failure, up to machine limits • Up to 15% strain, deformation is primarily accommodated by void space collapse • Void space collapse above the phengite dehydration reaction becomes strain rate sensitive  relative weakening • Instantaneous sample drainage or fast deformation counteracts weakening effect High-T mica dehydration facilitates shale compaction D-ERDW Geological Institute

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  11. Microstructures D-ERDW Geological Institute

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  13. Geological map New York State Isachsen et al., 1990 (New York Geological Survey) D-ERDW Geological Institute

  14. Dehydration model • DTA/DTG analysis • Mass loss = 3.1 wt.% D-ERDW Geological Institute

  15. Water loss (2) D-ERDW Geological Institute

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