Tracking CO₂ 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 (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.

Deformation‐Based Monitoring of Water Migration in Rocks Using Distributed Fiber Optic Strain Sensing: A Laboratory Study

“…Once the rock is saturated, any further changes in strain are nearly fully controlled by the pore pressure (poroelastic deformation), as is clear in Figure 8b. By incorporating Langmuir adsorption, Zhang et al (2019) developed a two-phase fluid flow and poromechanical coupled model to simulate flow and deformation.…”

“…The strain was amplified relative to natural rock in the subsurface, which is often initially hydrated. However, for a two-phase fluid flow regime (supercritical CO 2 and brine) in which the rock sample was initially saturated with brine, Zhang et al (2019) showed in an experimental study that the adsorption-induced strain change can be remarkably sensitive to the fluid migration front. The induced swelling may be an indicator for the migration of the fluid plume.…”

“…We used a natural low-permeability (0.02 mD) Tako sandstone sample (from Gunma, Japan) in the experiment (Figure 1a). The same sandstone is described in detail in another study on strain responses during CO 2 injection, which is part of the same series of experiments (Zhang et al, 2019). For the sake of completeness, we here briefly describe the method.…”

“…Kogure et al (2015) and Xue et al (2018) performed laboratory investigations to show that DFOSS may be promising for geomechanical monitoring under hydrostatic confinement and pore pressure conditions. In a previous study, we used DFOSS to monitor the migration of a CO 2 plume in rocks, particularly for the underground storage of CO 2 (Zhang et al, 2019). Fan et al (2019) applied the quasi-distributed fiber Bragg grating sensing method (with three monitoring points) to detect the front of a CO 2 plume.…”

“…Figure9. Scanning electron micrograph showing kaolinite platelets in the Tako sandstone sample(Zhang et al, 2019).…”