Detection and quantification of underground CO₂ leakage into the soil using a fiber-optic sensor

This study presents a field demonstration of underground CO₂ leakage detection using a fiber-optic interferometric sensor at an artificial leakage experiment site. CO₂ gas was injected for a couple of days into the unsaturated soil zone and CO₂ leakage monitoring was continuously performed for nine days using the fiber-optic sensor buried in the soil, using a hollow core photonic crystal fiber (HC-PCF) based sensor. Temperature and relative humidity in the soil were simultaneously measured by the commercial sensors. The measurement results of the HC-PCF sensor were evaluated by comparing with those by the commercial non-dispersive infrared sensor. This comparison illustrated that the proposed HC–PCF sensor was able to in-situ monitor CO₂ gas concentration with a range of 0–100%. Accordingly, the proposed fiber-optic sensor has the potentials to provide a reliable assessment of CO₂ gas leakage in geologic carbon storage sites and other gas leaking sites.