Chemical Compaction of Illite Shale an Experimental Study
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Research Collection Doctoral Thesis Chemical compaction of illite shale An experimental study Author(s): Bruijn, Rolf H.C. Publication Date: 2012 Permanent Link: https://doi.org/10.3929/ethz-a-007303652 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Chemical Compaction of Illite Shale: An Experimental Study by Rolf H.C. Bruijn 2012 Zurich, Switzerland Cover image: a broken surface SE image of PAT1 (C) sample P1328. It shows a high magnification of the characteristic, yet complex microstructure of synthesized metapelite comprised of silty and clayey quartz clasts and occasionally folded ultrafine mica and illite crystals as matrix material. DISS. ETH NO. 20144 Chemical compaction of illite shale: An experimental study A dissertation submitted to ETH ZURICH for the degree of Doctor of Sciences presented by ROLF HENDRIK CORNELIS BRUIJN M.Sc. Earth Sciences, Utrecht University, the Netherlands Date of birth 05.05.1983 Citizen of the Netherlands accepted on the recommendation of Prof. Dr. Jean-Pierre Burg examiner Dr. Philip M. Benson co-examiner Dr. Dan Faulkner co-examiner 2012 This work was financially supported by the Swiss National Science Foundation grants 200020-132772 and 200021-116153, awarded to Prof. Dr. J-P. Burg, Dr. L. Burlini and Dr. S. Misra. On this thesis rests copyright. The entire thesis except chapter 4 Copyright © 2012, R.H.C. Bruijn, following ‘Ordinance on Doctoral Studies, art. 34’, issued by ETH Zurich, Switzerland. Chapter 4 Copyright © 2011, Elsevier B.V., following ‘Journal Publishing Agreement’ issued by Elsevier B.V., the Netherlands, for article “Mechanical and microstructural development of Carrara marble with pre-existing strain variation”, with PII-number: S0040-1951(10)00390-2. Cover and book design: R.H.C. Bruijn Printed by printenbind.nl, Amsterdam Dedicated to Luigi Burlini may he rest in peace, and my mother and sisters, for allowing me to go on this adventure far away from home Table of contents Abstract 1 Kurzfassung 3 Chapter 1: Introduction 7 ____________________________________________________________________________________________________ 1.1: Literature background 8 1.2: Problem statement 10 1.3: Rationale 11 1.4: Thesis outlook 12 Chapter 2: Sediment compaction 15 ____________________________________________________________________________________________________ 2.1: Compaction kinetics in nature and experiments 16 2.2: Shale/mudstone compaction 24 2.3: Sandstone compaction 28 2.4: Limestone compaction 30 2.5: Very low-grade metamorphism 31 2.6: Rock magnetism 33 Chapter 3: Methods and analytical tools 35 ____________________________________________________________________________________________________ 3.1: Sample preparation and experiments 36 3.2: Compaction apparatus 38 3.3: Data recording and processing for compaction stage 3b 44 3.4: Methods for chemical analysis 47 3.5: Porosity and density measurements 49 3.6: SEM imaging 50 3.7: Magnetic properties 53 Chapter 4: Evaluation of instrumentation precision 57 ____________________________________________________________________________________________________ Mechanical and microstructural development of Carrara marble with pre-existing strain variation 4.1: Introduction 59 4.2: Method 61 4.3: Results 65 4.4: Discussion 78 4.5: Conclusions 89 4.6: Acknowledgements 90 Chapter 5: Material: illite shale 91 ____________________________________________________________________________________________________ 5.1: Illite shale selection 92 5.2: Physical state of the shales 92 5.3: Mineral phases and microstructure 94 5.4: Porosity/density and pores 98 5.5: Major element composition 100 5.6: Powder grain size 103 5.7: Choice of Maplewood Shale 105 5.8: Geological setting of Maplewood Shale 106 Chapter 6: Chemical model 109 ____________________________________________________________________________________________________ 6.1: Phase stability modeling 110 6.2: Pseudosection 110 6.3: Water dependency 112 6.4: Dehydration and dehydroxylation 114 6.5: Summary 115 Chapter 7: Results 117 ____________________________________________________________________________________________________ 7.1: Porosity and density 118 7.2: Finite volumetric strain 119 7.3: Finite sample deformation 120 7.4: Mechanical data and rheology 121 7.5: Chemistry 125 7.6: SEM mineral phase characterization 127 7.7: Microstructures 130 7.8: Pores 132 Chapter 8: Magnetism 135 ____________________________________________________________________________________________________ Chemical compaction of illite shale powder: magnetic characterization 8.1: Introduction 137 8.2: Method 137 8.3: Results 139 8.4: Discussion and conclusions 143 8.5: Acknowledgements 145 Chapter 9: Discussion 147 ____________________________________________________________________________________________________ 9.1: Porosity and density 148 9.2: Accommodation of finite volumetric strain 150 9.3: Sample deformation path 151 9.4: Deformation mechanisms 153 9.5: Chemistry 156 9.6: Microfabric elements 157 Chapter 10: Conclusions and outlook 161 ____________________________________________________________________________________________________ 10.1: Problem statement 162 10.2: Main findings 163 10.3: Conclusions 164 10.4: Recommendation for further research 165 References 169 Appendix A: List of physical quantities and established constants 187 Appendix B: List of compaction stage 3b experiments 190 Appendix C: Sample properties after compaction stage 2 and 3a 192 Appendix D: Sample properties after compaction stage 3b experiments 194 Appendix E: KFT water content 196 Acknowledgements 199 Curriculum Vitae 201 Abstract Sediment diagenesis has been classified nearly a century ago as a key process for the formation of rocks. In response to burial by overlying younger deposits, both mechanical and chemical processes contribute to the compaction and consolidation of sediments, the degree of which is controlled by both intrinsic and extrinsic parameters such as time, effective pressure, temperature, mineral composition and grain size distribution. Rock physical properties are strongly affected by clay diagenesis. So far, only the mechanical processes during clay diagenesis that dominate in the top 2-3 km of the sedimentary column have been simulated in the laboratory. However, studies on natural shales and mudstones have also emphasized the importance of chemical processes for diagenesis, although occurring in deeper domains and controlled more by temperature than by effective stress. Foreland basins are typical examples of a tectonic setting where sediments are buried deep enough for the activation of chemical processes. The effect of tectonic forces (deformation) on diagenesis is however enigmatic and to date poorly constrained by experimental simulation. The present study simulates the chemical processes in the laboratory and examines how tectonic forces affect compaction processes that transform porous illite shale powder into compact crystalline metapelite. The experimental compaction procedure consists of three stages. In the first compaction stage, dry illite shale powder (originating from Maplewood Shale, New York, USA) was mechanically compacted in a hydraulic cold-press with a vertical load of 200 MPa. The second stage employed a hot isostatic press (HIP) set at 170 MPa confining pressure and 590 °C, and ensured powder lithification. In the final stage, further compaction was achieved by either repeating HIP treatment or by performing confined deformation tests in a Paterson-type gas-medium apparatus. During the second HIP event temperature and pressure were set at 490 °C and 172 MPa. In the Paterson apparatus three different stress regimes were applied: confined compression, confined torsion or isostatic stress. For the first two regimes, deformation was enforced by applying a constant strain rate ranging from 7×10-6 to 7×10-4 s-1. Experiments were performed at 300 MPa confining pressure and a fixed temperature of 500 °C, 650 °C, 700 °C or 750 °C. These conditions were chosen from a thermodynamic forward simulation of the stability of mineral phases. In some Paterson apparatus tests, the effects of fluid availability and effective pressure were tested by respectively venting the sample or applying a 50 MPa argon pore pressure. Lithified samples were analyzed for their microstructural, chemical and physical development with compaction using scanning electron microscopy, Karl Fisher Titration, X-ray diffraction and gas pycnometry. Sample strength evolution was recorded during Paterson apparatus tests and strain measured afterwards. The magnetic signature of the compacting metapelites was quantified by measuring low and high-field anisotropy of magnetic susceptibility (AMS), and the ferrimagnetic contributions were identified using rock magnetic methods. 1 The three-stage compaction resulted in synthetic metapelites ranging in porosity from 1.0 % to 17.1 %. Linear increase in density and strong correlation between volumetric strain and pore reduction indicate that compaction was accommodated primarily by pore space closing. In deformation experiments axial strain was accommodated first by uniaxial shortening following pore collapse and later by radial extension, which in some cases resulted in total decompaction. Illite transformation to phengite and fluid assisted mass transfer resulted in diffusion creep type strain accommodation.