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ItemMicro-mechanical Modeling for Rate-Dependent Behavior of Salt Rock under Cyclic Loading( 2021) Shen, Xianda ; Ding, Jihui ; Arson, Chloé ; Chester, Judith S. ; Chester, Frederick M.The dependence of rock behavior to the deformation rate is still not well understood. In salt rock, the fundamental mechanisms that drive the accumulation of irreversible deformation, the reduction of stiffness and the development of hysteresis during cyclic loading are usually attributed to intracrystalline plasticity and diffusion. We hypothesize that at low pressure and low temperature, the rate-dependent behavior of salt rock is governed by water-assisted diffusion along grain boundaries. Accordingly, a chemo-mechanical homogenization framework is proposed, in which the Representative Elementary Volume (REV) is viewed as a homogeneous polycrystalline matrix that contains sliding grain-boundary cracks. The slip is related to the mass of salt ions that diffuse along the crack surface. The rate of diffusion is calculated by a pressure solution model. The relationship between fluid inclusion-scale and REV-scale stresses and strains is established by using the Mori-Tanaka homogenization scheme. The proposed rate-dependent homogenization model is calibrated against cyclic compression tests. It is noted from the model that a lower strain rate and a larger number of sliding cracks enhances stiffness reduction and hysteresis. Thinner sliding cracks (i.e. thinner brine films) promote stiffness reduction and accelerate stress redistributions in the crack inclusions. Higher roughness angles lead to an increased difference of normal stress along the different segments of the crack plane and to a reduced diffusion path, which both amplify the reduction of stiffness and the development of hysteresis. The larger the volume fraction of the crack inclusions, the larger the REV deformation and the larger the hysteresis. Results presented in this study shed light on the mechanical behavior of salt-rock that is pertinent to the design of geological storage facilities that undergo cyclic unloading, which could help optimize the energy production cycle with low carbon emissions.
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ItemMicro-mechanical Modeling for Rate-Dependent Behavior of Salt Rock under Cyclic Loading(Georgia Institute of Technology, 2020) Shen, Xianda ; Ding, Jihui ; Arson, Chloé ; Chester, Judith S. ; Chester, Frederick M.The dependence of rock behavior on the deformation rate is still not well understood. In salt rock, the fundamental mechanisms that drive the accumulation of irreversible deformation, the reduction of stiffness and the development of hysteresis during cyclic loading are usually attributed to intracrystalline plasticity and diffusion. We hypothesize that at low pressure and low temperature, the rate-dependent behavior of salt rock is governed by water-assisted diffusion along grain boundaries. Accordingly, a chemo-mechanical homogenization framework is proposed, in which the Representative Elementary Volume (REV) is viewed as a homogeneous polycrystalline matrix that contains sliding grain-boundary cracks. The slip is related to the mass of salt ions that diffuse along the crack surface. The relationship between fluid inclusion-scale and REV-scale stresses and strains is established by using the Mori-Tanaka homogenization scheme. It is noted from the model that a lower strain rate and a larger number of sliding cracks enhance stiffness reduction and hysteresis. Thinner sliding cracks (i.e. thinner brine films) promote stiffness reduction and accelerate stress redistributions. The larger the volume fraction of the crack inclusions, the larger the REV deformation and the larger the hysteresis. Results presented in this study shed light on the mechanical behavior of salt-rock that is pertinent to the design of geological storage facilities that undergo cyclic unloading, which could help optimize the energy production cycle with low carbon emissions.
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ItemFabric evolution and crack propagation in salt during consolidation and cyclic compression tests( 2020) Shen, Xianda ; Ding, Jihui ; Lordkipanidze, Ilia ; Arson, Chloé ; Chester, Judith ; Chester, FrederickIt is of great interest to describe and quantify the evolution of microstructure for a better understanding of rock deformation processes. In this study, 2D microstructure images of salt rock are analyzed at several stages of consolidation tests and cyclic compression tests to quantify the evolution of the magnitude and orientation of solidity, coordination, local solid volume fraction and crack volume. In both the consolidation and the cyclic compression tests, the deformation of aggregates achieved by grain rearrangement is greater than that achieved by the deformation of an individual grain. In the consolidation tests, the aggregates are rearranged into horizontal layers of coordinated grains, the orientation distribution of grain indentations is quasi-uniform, and the size of the pores reduces and becomes more uniformly distributed. As a result, salt rock microstructure becomes more homogeneous. The increase of local solid volume fraction in the lateral direction is correlated with an increase of the oedometer modulus. In the cyclic compression tests, grain-to-grain contact areas decrease due to the redistribution of grains and the propagation of intergranular cracks. Aggregates are reorganized into columns of coordinated grains. Intergranular opening-mode cracks tend to develop in the axial direction, while intergranular shear-mode cracks propagate preferentially in the lateral direction. The lateral components of the fabric tensors of coordination and local solid volume fraction decrease, which results in an increase of the Poisson's ratio. The fabric descriptors used in this work allow a better quanti cation and understanding of halite deformation processes and can be used in other types of rocks encountering similar deformation mechanisms.
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ItemMechanisms of anisotropy in salt rock upon micro-crack propagation( 2020) Shen, Xianda ; Arson, Chloé ; Ding, Jihui ; Chester, Frederick M. ; Chester, Judith S.