Enhanced hydrogeochemical baseline of a CO2 injection facility in southern Alberta, Canada

Abstract

Geological storage of CO₂ is anticipated to play a significant role in the management and reduction of greenhouse gas emissions. Monitoring of CO₂ injection facilities is essential to provide reassurance of the containment of the injected CO₂. Here, we report results over six years (2018–2023) for a hydrogeological and geochemical (gas compositions, δ¹³C_CH4, δ¹³C_CO2, δ²H_CH4 and noble gas concentration and isotopes) monitoring program at a small-scale CO₂ injection facility located near Brooks, Alberta, Canada with injection ∼300 m below ground. The results provide a comprehensive record of the subsurface hydrological and geochemical conditions over the six-year period. Injected CO₂ was not detected in samples from the injection zone. There was also no indication of injected CO₂ in samples collected from surface casing vents of the three ∼300 m deep wells, nor was injected CO₂ observed in samples from the six shallow groundwater wells (<105 m deep). Various compositional and isotopic changes have been observed over time which are interpreted to either be indirectly related to CO₂ injection or completely unrelated indicating non-CO₂ injection related variability in the baseline conditions of the site. Additionally, a progressive reduction in hydraulic head has been observed in some shallow aquifers consistent with drought conditions in the region. Our study implies that complex subsurface changes may occur at CO₂ storage sites which may be unrelated to human activity, complicating the monitoring of CO₂ injection.