[H-SC06] CCUS (Carbon Dioxide Capture, Utilization, and Storage) for Climate Mitigation

[HSC06-P02] Observation of deformation pattern due to fluid phase change in sedimentary rock core specimen using optical fiber sensor

*Hyuck Park¹, Ziqiu Xue¹ (1.Research Institute of Innovative Technology for the Earth)

Keywords:Optical fiber sensor, X-ray CT imaging, CO2 migration, 2 phase fluid

If it is known how the deformation pattern of a rock changes as the type of fluid in the rock changes, it can be detected using the difference of deformation pattern when CO₂ infiltrates the water-saturated underground. With this in mind, we performed CO₂ injection laboratory experiments using core-scale sandstone. Single optical fiber was used as distributed fiber optic sensors in this study. CO₂ migration in the specimen was confirmed by X-ray CT images. The purpose of this experiment is to confirm the difference in the reaction of the optical fiber according to the change of the type of fluid in the specimen. Sarukawa sandstone (diameter: 34.8mm, length: 179.5mm) was used in this study. It has a relatively homogeneous structure and has irregularly shaped grains and voids. Microbubble filter (diameter: 34.3mm, length: 5.0mm) was located in between distributor and core specimen in the upstream side. Porosity of the specimen determined by X-ray CT imaging is 23.38%. The permeability is about 5.3mDarcy. The purpose of this experiment is to confirm the difference in the reaction of the optical fiber according to the change of the type of fluid in the sample. The experiment was conducted under the pressure and temperature conditions that simulate underground environments; pore pressure: 10MPa, temperature: 40 degrees Celsius. The confining pressure selected in this study was 12MPa. The specimen was first saturated with KI aqueous solution (11.5 wt%). We continuously checked the reaction of the optical fiber from when the specimen was saturated with KI aqueous solution to during the permeability measurement. Next, supercritical CO₂ was injected into the specimen saturated with KI aqueous solution, and CO₂ migration was measured using both X-ray CT and optical fiber. In both cases (KIaq only, KIaq+CO₂), the differential pressure between the upstream and downstream was 0.5 MPa. ・When one type of fluid (KIaq) flows through the specimen, the optical fiber reaction exhibits a strain gradient in the form of expansion from the upstream side and decreasing degree of expansion toward the downstream side. The shape of the strain gradient was kept constant. ・When two types of fluids (KIaq, CO₂) were present, the shape of the strain gradient gradually increased as the CO₂ migration progressed. The movement of the deformation front (optical fiber) matched the CO₂ migration (X-ray CT). The difference in the expandability of the two fluids may be the cause of the difference in the response of the optical fiber. We concluded that the optical fiber sensor has potential as a tool to detect the migration of CO2 in and around the CO₂ storage facility.