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.