Tracking CO2 plume footprints in reservoir-caprock system by fibre optic strain sensing
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Description: Underground fluid storage and utilization, e.g., geological storage of carbon dioxide (CO2) and natural gas, require effective tools to monitor the vertical pressure, deformation, and saturation migrations, and verify the secure containment of the reservoir-caprock system. Here we demonstrate how to utilize the swelling strain signals attributed to the footprints of pressure build up and the adsorption of supercritical CO2 in natural clay-rich rocks to track the displacement of supercritical CO2/brine under typical conditions of CO2 geological storage. Our study effectively captured the breakthrough of CO2 plume from the analogue “reservoir” part to the “caprock” part using the distributed strain, measured by a high-resolution single-mode Rayleigh-scattering based optical fibre sensor. The magnitude of strain change induced by CO2 adsorptions on the clay minerals is found to be significantly greater than that caused by pore pressure changes alone. The findings suggest that the measured strain changes can not only reveal the in situ deformation state but also be a valid indicator for tracking the movement of CO2 plume as it enters the clay-rich critical region in reservoir-caprock systems, and thus serves as an early warning to the potential occurrence of large deformations caused by high pressure build up.