Field assessment of sensor technology for environmental monitoring using a process -based soil gas method at geologic CO2 storage sites

A process-based approach to soil gas monitoring at geologic CO2 storage sites is an accurate, simple, and cost-effective alternative to other "concentration-based" soil gas methods which require complicated long-term baseline data collection and analysis. The current limitation to implementing a process-based method on an industrial scale (e.g. gigatons of storage) is a lack of technology for economical field-deployable smart data collection of all required gas concentrations (CO2, CH4, O-2, N-2). To address this gap, the Carbon Transport and Storage Corporation Pty Ltd (CTSCo) deployed commercially-available automated sensors at their proposed future Glenhaven CO2 storage site, located 21 km SW of the town of Wandoan, Queensland, Australia. The goal was to assess the suitability of currently-available sensors for implementing a process-based monitoring approach with the aim of providing real-time answers on source attribution of surface anomalies that could represent CO2 migration to surface. Here we report the results of a first-ever long-term (2 years) test of commercially available sensors for the purpose of process-based soil gas environmental monitoring. The accuracy and precision of data collected with an array of sensors for measuring CO2, CH4, and O-2, with additional sensors for measuring temperature, relative humidity, and pressure were compared against the current method using gas chromatography. The results indicate that currently-available sensors are not adequate for attaining the long-term monitoring goals set forth by a process-based monitoring approach and additional technology development is recommended.