[H-SC07] CCUS (Carbon Dioxide Capture, Utilization, and Storage) for Climate Mitigation

[HSC07-P07] Strain detection by optical fiber for CO₂ injected core specimen

*Hyuck Park¹, Yankun Sun¹, Ziqiu Xue¹ (1.Research Institute of Innovative Technology for the Earth)

Keywords:Optical fiber, CO2 flooding, strain detection, strain profile, X-ray CT

In order to detect strain of rock specimen during CO₂ injection using optical fiber, a laboratory experiment was carried out using porous sandstone. Spiral direction strain of core specimen was detected by optical fiber. We compared the strain profiles in the case of one-phase flow (water only) and the case of two-phase flow (CO₂ in water saturated specimen). CT image analysis was also used to determine the internal state of the specimen. Sarukawa sandstone (diameter: 34.83mm, length: 179.50mm) was used in this study. Porosity of the specimen determined by X-ray CT imaging is 23.38%. This specimen is homogeneous overall, but there are some gravels in some places. The permeability is about 7 mDarcy. 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 is 12MPa. The specimen was first saturated with KI aqueous solution (11.5 wt%). The permeability was confirmed using the KI aqueous solution. The upstream pump was prepared at 10.5 MPa for differential pressure of 0.5MPa. The CO₂ flooding was carried out until the total fluid injection reaches about 7.6PV (pore volume). Optical fiber measurement and X-ray CT imaging were performed in all experimental steps. In the case of one-phase flow (water only), as soon as the water injection started, the strain profile was completed. And the strain profile was almost constant until the test ended. In the case of two-phase flow (CO₂ flooding in water saturated specimen), there was a small strain increase up to CO₂ breakthrough and there was a sudden strain increase after the breakthrough. In this study, it was possible to measure the spiral direction strain of 180mm long core specimen. At the same time, we could visualize the process of CO₂ flooding by X-ray CT image analysis. It has become possible to measure distortion of a long distance under the ground with a single optical fiber. It reveals that the optical fiber sensing is a potential tool for future CO₂ storage industries.