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 buildup 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.

Rock deformation induced by pore‐fluid pressure carries useful information about fluid flow owing to hydromechanical coupling. Thus, obtaining spatiotemporal changes in rock deformation could provide improved understanding of the fluid and pressure migration in aquifers or the role of fluid in the evolution of rainfall‐induced landslide. Here we deployed high‐resolution Rayleigh‐scattering‐type distributed fiber optic strain sensing (DFOSS) to measure rock deformation while injecting water into low‐permeability dry sandstone. X‐ray computed tomography imaging was simultaneously used to visualize the water migration. DFOSS measurements showed the rock developed a dilation deformation that grew during water saturating process. The movement of water wetting front can be revealed by the changes in the measured distributed strain. Strain changes were shaped by poroelastic changes due to the fluid pressure buildup and swelling by the water–clay reaction (i.e., adsorption). The latter mechanism caused increase in the strain when water first entered the dry pore spaces and the change in pore pressure was slight. The mechanism continued contributed to the overall deformation to peak magnitude of ~600 μϵ together with poroelastic mechanism. However, after the rock was fully saturated, further deformation during the flow test can be explained by the poroelastic mechanism alone. Our study suggests that the two factors can be employed as signatures for effectively monitoring fluid behavior in natural sediments using DFOSS. Moreover, we obtained the spatial hydromechanical properties, permeability and stiffness, from the distributed strain measurement and pressure responses. Using DFOSS in the field may substantially improve our ability to monitor and model fluid activity related to rock deformations in reservoirs and rainfall‐induced landslides that would help in warning people of risks and preventing disasters.

In this study distributed fiber optic sensing has been used to measure strain along a vertical well of a depth of 300 m during a pumping test. The observed strain data has been used in geomechanical simulation, in which a combined analytical and numerical approach was applied in providing scaled-up formation properties. The outcomes of the field test have demonstrated the practical use of distributed fiber optic strain sensing for monitoring reservoir formation responses at different regions of sandstone–mudstone alternations along a continuous trajectory. It also demonstrated that sensitive and scaled rock properties, including the equivalent permeability and pore compressibility, can be well constrained by the combined use of water head and distributed strain data. In comparison with the conventional methods, fiber optic strain monitoring enables a lower number of short-term tests to be designed to calibrate the parameters used to model the rock properties. The obtained parameters can be directly used in long-term geomechanical simulation of deformation of reservoir rocks due to fluid injection or production at the CO₂ storage and oil and gas fields.