Investigation of multiphysics processes including chemical, thermal, hydraulic and mechanical interactions in geomaterials in particular shales has considerably expanded in recent years. The core scale multiphysics experimentation is often very complex to conduct and more importantly involves significant uncertainty. In addition, the micro-scale mechanisms deriving the macro-scale phenomena are yet to be explored. The missing links between micro-macro scale processes have led to mostly modelling approaches with uncertain input parameters. We therefore, for the first time, design a novel shear device coupled with interferometry technique to investigate the multiphysics phenomena from µm to cm scale in real time. In the new setup, the special shearing cell accommodates a 1cm×1cm×4mm cubic sample resembling the plane strain condition. The cubic sample can undergo hydrostatic or shear stresses while being continuously exposed to high pressure working fluids circulating in the cell. An imbedded sapphire window allows the observation of the micro-fracture development and pore structure alteration in real time using green light interferometry technique. The technique can be readily coupled with static image scanning such 3D micro-ct scanning for further insight. In an example application, a shale sample was placed in the cell and was exposed to deionized (DI) water at hydrostatic and shear stress states and images were taken from the sample using interferometer. The obtained images were then registered and Digital Image Correlation (DIC) technique was used to analyze the developed strains during the experiment. The results showed for instance that hydration induced stresses are unlikely to cause any micro-fracture initiation under hydrostatic stresses however micro-fractures appeared under shear stress. This behavior seems to attribute to loss of sample’s strength when exposed to water rather than a phenomenon caused by increase in internal hydration stresses. The obtained results have a wide applications such as the design of hydraulic fracturing and completion fluids, the gas flow in micro- fractures/micro-pores and characterization of the hydration induced micro-crack development at µm- to cm-scale at different stress states.
Digital Multiphysics Interferometry: A New Approach to Study Chemo-Thermo-Hydro-Mechanical Interactions in Geomaterials
Roshan, H., Siddiqui, M. A. Q., Regenauer-Lieb, K., Lv, A., Hedayat, A., and M. Serati. "Digital Multiphysics Interferometry: A New Approach to Study Chemo-Thermo-Hydro-Mechanical Interactions in Geomaterials." Paper presented at the 52nd U.S. Rock Mechanics/Geomechanics Symposium, Seattle, Washington, June 2018.
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