Yi Zhang, Ziqiu Xue, Hyuck Park, Jiquan Shi, Tamotsu Kiyama, Xinglin Lei, Yankun Sun, Yunfeng Liang

Monitoring the migration of pore pressure, deformation, and saturation plumes with effective tools is important for the storage and utilization of fluids in underground reservoirs, such as geological stores of carbon dioxide (CO2) and natural gas. Such tools would also verify the security of the fluid contained reservoir–caprock system. Utilizing the swelling strain attributed to pressure build‐up and the adsorption of supercritical CO2 on clay minerals, we tracked the fluid plume in a natural clay‐rich Tako sandstone at the laboratory core‐scale. The strain was measured by a high‐resolution distributed fiber optic strain sensing (DFOSS) tool. The strain changes induced by CO2 adsorptions on clay minerals were significantly greater than those caused by pore pressure alone. The distribution of the swelling‐strain signals effectively captured the dynamic breakthrough of the CO2 plume from the high‐ to low‐ permeability regions in the Tako sandstone. Besides revealing the in situ deformation state, the measured strain changes can track the movement of the CO2 plume as it enters the clay‐rich critical regions in the reservoir–caprock system. The present findings and potential future applications of DFOSS in the field are expected to enhance the monitoring and management of underground fluid reservoirs.