Assessing Petroleum Geochemical Techniques for CCS Monitoring: Results from a Controlled CO₂ Release Experiment

Global warming is one of the most pressing challenges of our time, demanding urgent and innovative solutions. Carbon Capture and Storage (CCS) is a key mitigation strategy, but its safe implementation requires robust Monitoring, Measurement and Verification (MMV) systems. This work demonstrates how geochemical tools widely established in the oil and gas industry, including gas chromatography (GC), direct CO₂ detection, carbon isotope analysis (δ¹³C-CO₂), noble gas composition and isotopes, can be effectively repurposed for surface geochemical monitoring in CCS projects. A controlled CO₂ release experiment was conducted at Barra do Furado (Rio de Janeiro, Brazil), as part of the CCS Cabiúnas–São Tomé pilot project monitoring program. CO₂ was injected into the water table (∼1.20 m depth) and monitored at 27 georreferenced points in radial arrays (1, 2.5, 5, and 10 m). CO₂/CH₄/O₂/H₂/H₂S concentrations were measured in situ by the portable GA 5000 analyzer. Soil gas samples collected in vacutainer vials were analyzed by Gas Chromatography (C1–C5, CO₂, N₂, H₂) and headspace techniques. Carbon isotope ratios (δ¹³C-CO₂) were determined by GC-C-IRMS. Noble gas composition and isotopes (He, Ne, Ar) were analyzed by multi-collector mass spectrometry (Helix MC Plus) as complementary tracers for CO₂ origin discrimination. The GA 5000 established a stable baseline of 0.23 ± 0.03% CO₂. After injection, concentrations reached up to 1.2% (∼45 h post-injection), representing 67–162% increases over baseline, with a predominantly radial dispersion pattern. GC systematically underestimated CO₂ relative to GA 5000, probably due to sampling procedure. Isotope analysis (background δ¹³C: −13.98) did not unambiguously detect the injected CO₂ signature (δ¹³C = −34.21‰) due to low concentrations. Noble gas offers promising complementary discrimination tools for future campaigns. These results demonstrate that petroleum exploration geochemistry provides a robust methodological framework for CCS monitoring, reinforcing the transferability of oil and gas analytical expertise to climate solutions.