Tracking CO 2 Plumes in Clay-Rich Rock by Distributed Fiber Optic Strain Sensing (DFOSS): A Laboratory Demonstration

Abstract

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 (CO 2 ) and natural gas. Such tools would also verify the security of the fluid contained reservoir-caprock system. Utilizing the swelling strain attributed to pressure buildup and the adsorption of supercritical CO 2 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 CO 2 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 CO 2 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 CO 2 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.