Analysis of signal-to-noise ratio of δ¹³C-CO₂ measurements at carbon capture, utilization and storage injection sites

As new regulations from the United States Environmental Protection Agency require monitoring and accounting for Class VI injection wells, determining the efficacy of monitoring techniques is a crucial barrier to wide scale carbon capture, utilization and storage (CCUS) deployment. The monitoring of CO₂ injection sites to ensure safety and operational success requires high temporal resolution CO₂ concentration and carbon isotopic (δ¹³C) measurements. As rapid measurement of δ¹³C is not possible with standard isotope ratio mass spectrometry (IRMS), we have developed a methodology using cavity ringdown spectroscopy (CRDS) with a manifold system in order to obtain accurate rapid measurements from a large sample area over an extended study period. A modified Picarro G1101-i CRDS with updated software and an auxiliary laser allows for rapid and continuous field measurement of concentrations and δ¹³C of carbon dioxide as well as concentrations of water and methane. A manifold system actuated by a 16 position valve allows for an increased sampling region and internet connectivity and software developments permit immediate access to data from a remote location. At a field site in Texas where preparations have been underway for enhanced oil recovery (EOR) operations, we have been able to observe biogenic effects on a diurnal scale, as well as variation due to precipitation and seasonality. Our system has proven field readiness for the monitoring of sites with modest CO₂ flux. These data have been used to improve leak detection thresholds by an order of magnitude over published models.