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

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• The fiber-optic sensor was implemented in the field for underground CO 2 gas leakage monitoring. • Hollow-core photonic crystal fiber was used to improve the sensitivity of the sensor. • The integrated sensor package was used to cancel complex crosstalk due to the temperature and humidity changes. • The proposed fiber-optic sensor has the potential to monitor the gas leakage continuously and remotely. This study presents a field demonstration of underground CO 2 leakage detection using a fiber-optic interferometric sensor at an artificial leakage experiment site. CO 2 gas was injected for a couple of days into the unsaturated soil zone and CO 2 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 CO 2 gas concentration with a range of 0–100%. Accordingly, the proposed fiber-optic sensor has the potentials to provide a reliable assessment of CO 2 gas leakage in geologic carbon storage sites and other gas leaking sites.