Infrared monitoring of underground CO2 storage using chalcogenide glass fibers

An optical-fiber-based system suitable for monitoring the presence of carbon dioxide, so-called “greenhouse gas”, is investigated. Since each pollutant gas shows a characteristic optical absorption spectrum in the mid-infrared (mid-IR), it is possible to detect selectively and quantitatively the presence of gases in a given environment by analysing mid-IR spectra. The main infrared signature of carbon dioxide gas is a double absorption peak located at 4.2 μm. Chalcogenide optical fibers, which can transmit light in the 1–6 μm range, are well-adapted for CO2 analysis. In this wavelength range, they show attenuation losses that compare favourably with other types of fiber such as silver halide fibers. In this paper, the detection limit of CO2 is established as a function of optical path length. The dynamic parameters of the sensors, such as reversibility, response time and recovery time, are also studied. It is concluded that optical fibers based on chalcogenide glasses could be used to transport infrared light from a black body source to a remote CO2 geological storage zone in order to monitor, in real time, CO2 gas leakage.