The mining operations required to recover mineral resources, store energy underground and dispose of waste in deep geological layers involve coupled mechanical, physical and chemical rock microstructure changes. Damage and healing in rocks refer to variations of mechanical and physical properties induced by pore or crack evolution. The gap between microscopic and macroscopic models makes it infeasible to uniquely characterize the pore- and crack- scale mechanisms that control deformation and flow regimes, predict percolation thresholds coupled to changes of rock stiffness, or relate crack rebonding time to stiffness and permeability healing time.
Therefore the objectives of the work presented in this lecture are to: Understand and predict chemo-mechanical changes of pore geometry; Model the dynamics of pore networks; Formulate and assess innovative microstructure-enriched models of damage and healing; and Interpret rock deformation and fluid flow instabilities resulting from chemo-mechanical damage and healing. Geological storage in salt is used as an illustrative problem for investigating the following fundamental scientific questions: Why do pores and cracks heal? How long do mechanical and hydraulic recovery take? How much energy does healing require? We first explain a top-to-bottom multi-scale approach: fabric-enriched damage and healing damage mechanics. Moments of probability of microstructure descriptors, found by image analysis, are used as internal variables. The mathematical framework makes it possible to predict the evolution of pore geometry and connectivity upon multi-physics damage and healing processes. We then present a bottom-to-top multi-scale approach based on the self-consistent method. Models allow simulating damage and subsequent accommodation in a polycrystal subject to time-dependent sliding mechanisms.
Finally, we focus on the processes driving flow network growth and transformation upon damage and healing processes. These are still poorly understood, especially under dynamic injection and withdrawal cycles. What fracture network topology optimizes fluid flow in a rock mass? Do networks morph towards asymptotic topologies if subjected to steady or cyclic flow? Astonishing similarities were noted between the geometry of networks formed by living organisms (e.g. roots, slime mold) and that of infrastructure facilities (e.g. railway systems). Therefore we hypothesize that natural systems can be emulated to understand flow network formation and evolution in a porous geomaterial subject to damage and healing. We present preliminary work done on root system architecture, leaf venation topology and slime mold networks.
Dr. Chloé Arson is an Associate Professor in the School of Civil and Environmental Engineering at the Georgia Institute of Technology. She earned a Master of Science in soil and rock mechanics (2006) and a Ph.D. in geomechanics (2009) at Ecole des Ponts Paris Tech (France). After being a faculty at Texas A&M University, she joined Georgia Tech in 2012. She teaches Mechanics of Materials, Finite Element Methods and Tunneling. Dr. Arson is a theoretical and numerical expert in damage and healing rock mechanics, thermo-chemo-poromechanics, underground storage and bio-inspired subsurface networks. She regularly gives lectures in Europe and the U.S., organizes sponsored research workshops, and serves as a reviewer for more than 25 journals. At Georgia Tech, she leads the Rock Mechanics and Geostorage Simulation undergraduate laboratory, and is supported to study ethics and hydraulic fracturing. Dr. Arson received two PhD research prizes in 2010 and the NSF CAREER award in 2016.