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Janos L. Urai is an emeritus Professor of Structural Geology, Tectonics and Geomechanics of  RWTH Aachen University in Germany. Over his career Prof. Urai has worked in basic and applied interdisciplinary projects on problems related to the interaction of fluids and rock deformation, at a wide range of scales, using field studies, laboratory measurements, analogue modelling and numerical simulation. Prof. Urai has coached over 30 PhD students. Prof. Urai enjoys initiating interdisciplinary research projects in basic and applied Geoscience, building an Institute, designing innovative instruments, teaching Geoscience at all levels in Europe and the Middle East, coaching young talent in intercultural environments and presenting geoscience issues with societal relevance to the public. Prof. Urai was awarded the Huygens Fellowship of the Dutch Organisation of Basic Science, and senior research scientist at Shell Research. He was the Inaugural Dean of the Faculty of Science of the newly established the German University of Technology in Muscat, Oman. There he set up and organized the Department including the hiring of staff at all levels, establishing an accredited BSc and an MSc programme in a complex and multicultural environment. Over the past twenty years, many of his research projects were in Oman, where he worked on topics ranging from salt tectonics, tectonics of the Oman Mountains, fracture networks and fracture sealing in carbonates, to reservoir microporosity.

Introduction of the Lecture

Syntaxial crack-seal veins are first-order structures in deep, hydrothermal and reactive (THMC) environments where fluids create and moderate permeability and reactions interact with deformation. We modelled these veins using different approaches: we used the Phase Field Method (PFM) to model fracturing and epitaxial growth from an aqueous solution, based on thermodynamic and kinetic principles. We used the Discrete Element Method (DEM) to model the growth of cracks in rocks with veins in 3D.  Recently we performed coupled Phase Field models, to study the coupled thermal, hydraulic, mechanical and chemical evolution of syntaxial crack-seal veins. Observations of syntaxial vein microstructures provide data on microstructure, vein crystal morphology and facet crystallography for comparison of our results with natural prototypes. The coupled models lead to a better understanding of the feedback mechanisms between fracturing and sealing processes, quantify the evolution of mechanical and transport processes, help define new diagnostic microstructures in natural veins and form the basis for upscaling our models.

Janos L. Urai ¹, Michael Späth², Liene Spruzeniece¹, Britta Nestler³

¹ Institute of Applied Materials – Computational Materials Science (IAM), Karlsruhe Institute of Technology (KIT), Straße am Forum 7, 76131 Karlsruhe Germany

² Institute of Tectonics and Geodynamics, RWTH Aachen University, Lochnerstraße 4-20, Aachen, Germany

³ Institute of Digital Materials Science (IDM), Karlsruhe University of Applied Sciences, Moltkestraße 30, 76133 Karlsruhe, Germany

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Jishan Liu is a Professor at School of Engineering, the University of Western Australia. His main interests are multiphysics modelling of fractured media with applications to unconventional gases extraction, carbon neutrality and coal mine safety. His official profile can be found at:
https://research-repository.uwa.edu.au/en/persons/jishan-liu/

Introduction of the Lecture

Available permeability data sets of low permeable rocks such as coal and shale are apparently disordered and cannot be fully explained by the conventional theory of poroelasticity under common assumptions. This lecture will detail how this inability of poroelasticity is resolved through permeability map. Basic steps include (1) introduction of multi-scale REV (representative elementary volume) concept; (2) removal of thermodynamic equilibrium assumption; (3) introduction of thermodynamic equilibrium index (TEI); (4) development of the TEI-based permeability model; (5) development of the TEI-based experimental approach of permeability evolution; (6) modelling of non-equilibrium multiphysics involved; and (7) construction of a permeability map. Results demonstrate that available permeability data sets seem random but are in fact an integral part of the permeability map and that the TEI-based permeability model is the key cross-coupling relation for non-equilibrium multiphysics of fractured media.            

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Dr. Selvadurai is recognized for contributions to continuum mechanics, theoretical, computational and experimental geomechanics and applied mathematics for which he has received the Humboldt Senior Scientist Award, The Max Planck Prize in the Engineering Sciences, The Killam Prize, The Biot Medal, The Reissner Medal and The Desai Medal. His research includes the mechanics of elastic media undergoing large deformations, fracture mechanics, micromechanics of inclusions and defects, poroelasticity, coupled THM processes in deformable media, mechanics of inhomogeneous media, interfaces in geomechanics, fragmentation of brittle geomaterials, transport in porous media and mechanics of geosynthetics subjected to chemical exposure. He has published extensively in archival journals (http://www.mcgill.ca/civil/people/selvadurai/list-research-publications). He is the author or co-author of texts on Elastic Analysis of Soil-Foundation Interaction (Elsevier, 1979), Elasticity and Geomechanics (with R.O. Davis) (CUP, 1996), Partial Differential Equations in Mechanics Vols. 1&2 (Springer, 2000); Plasticity and Geomechanics (with R.O. Davis) (CUP, 2002), Transport in Porous Media (with Y. Ichikawa) (Springer 2012) and Thermo-Poroelasticity and Geomechanics (with A.P. Suvorov) (CUP, 2016). He is a Fellow of the Royal Society of Canada, The Canadian Academy of Engineering, The Engineering Institute of Canada, The American Academy of Mechanics, The Canadian Society for Civil Engineering and The Institute for Mathematics and its Applications (UK). He is a Chartered Engineer and a Chartered Mathematician.

Introduction of the Lecture

Geomaterials exhibit heterogenous properties at all scales and the THM characterization processes can be influenced by the heterogeneities that can influence the specification of properties at the modelling scale and at the experimental bench-scale. Heterogeneity can also be introduced by processes such as micro-mechanical damage and defect development. The lecture will discuss the estimation of key parameters such as the elasticities, the Biot coefficient, the permeability and thermal conductivity of heterogeneous limestones and granitic rocks.

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Chin-Fu Tsang received his B.Sc. first class honour degree in Physics in 1964 from the University of Manchester in UK and his PhD in 1969 from the University of California Berkeley in US. He spent his entire research career with Lawrence Berkeley National Laboratory, retiring in 2005 as Senior Scientist Emeritus in the Earth Sciences Division. Since retirement, he has continued his research first as a visiting professor of hydrogeology at Imperial College London in UK and then as a visiting professor and visiting scholar at Uppsala University in Sweden. He was also the founding chairman of the DECOVALEX project, serving as its chairman from 1992 to 2007.

Introduction of the Lecture

The study of coupled thermo-hydro-mechanical-chemical (THMC) processes in fractured rocks was identified as an important area of scientific research in the 1980’s, initially in the safety assessment of nuclear waste geological repository. It was then recognized as a crucial component of other geotechnical projects, such as enhanced geothermal energy development, fracking in unconventional gas development and waste water injection disposal, with related induced seismicity. Sustained efforts over the last decades cover a wide range of research topics, including fundamental studies, laboratory investigations, numerical model developments, field scale experiments and modeling. A typical example is the multinational cooperative research project DECOVALEX, that was initiated in 1992 and is still on-going with active participation of twelve countries. The present lecture will provide a look to the past years in this research field to review “where we have come from” and a discussion on some of the major challenges facing us today. These challenges include the role of natural fractures network at different flow percolation levels in hydromechanical processes, the interaction of flow bottlenecks and stress concentration points in fractured rocks, and changes in flow channeling effect due to mechanical deformation and chemical precipitation and dissolution.

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Wen-lu Zhu is professor of Geology at the University of Maryland. She received her PhD at Stony Brook University in New York. Upon graduation, she worked as a research scientist at the Woods Hole Oceanographic Institution before joining the faculty at the University of Maryland. Wen-lu’s research focuses on the relationships between deformation and fluid flow. She conducts laboratory experiments and quantifies the change of the microstructure of deforming rocks in 3-D at in-situ pressure and temperature conditions. For her work in the field of rock deformation, she was awarded the 2020 Louis Néel Medal by the European Geosciences Union.

Introduction of the Lecture

Recent experimental studies show that high pore fluid pressure causes a transition from rapid and dynamic to quasi-stable faulting in compact rocks such as granites.  The stabilizing effect of pore fluid pressure on faulting can be explained by dilatant hardening—fault nucleation leads to creation of new void space, resulting in a decrease in pore fluid pressure and an increase in effective normal stress, which impedes further fault growth. It has been shown is that dilatant failure stabilization requires the deformation to be undrained, i.e., the rate of pore fluid pressure re-equilibration must be slower compared to the rate of deformation. Under laboratory loading rates, undrained conditions can be readily achieved in low permeability compact rocks. However, tectonic strain rates can be 6-10 orders of magnitude slower than laboratory strain rates. Thus, the stabilizing effect of pore fluid pressure observed in compact rocks may not be directly applicable in modeling rupture processes in nature. To circumvent the obvious physical limitation of conducting experiments at tectonic strain rates, we deformed porous sandstones with permeability 6-10 orders of magnitude higher than that of compact rocks at typical laboratory strain rates. Our experimental results show that porous sandstones subjected to high pore fluid pressures fail by slow faulting under fully drained conditions. We conducted quantitative microstructural analysis on deformed samples. Based on our findings, we proposed that the stress corrosion cracking played an important role in the pore fluid pressure stabilizing effect on fault propagation in porous rocks.