Isotopic Tracing of the Fate of Injected CO in Mature Oilfields in Canada

Monitoring and verification of CO₂ storage is an essential component of geological storage projects. Evidence is presented from several enhanced oil recovery projects in Canada that geochemical and isotopic techniques can be successfully used to trace the fate of injected CO₂ . Geochemical and isotopic data for fluids and gases obtained from multiple wells at the Penn West Pembina Cardium CO₂ -Enhanced Oil Recovery Monitoring Pilot (Alberta, Canada) and from other pilot project sites were collected before and throughout the CO₂ injection phase. Carbon isotope ratios of injected CO₂ were markedly different from those of background CO₂ . After commencement of CO₂ injection, the concentrations and carbon isotope values of CO₂ and HCO₃^- in fluids and gases repeatedly obtained from monitoring wells were determined. Increasing CO₂ and often also HCO₃^- concentrations in concert with carbon isotope values trending towards those of the injected CO₂ revealed effective solubility and ionic trapping of injected CO₂ at several monitoring wells at the study sites. In addition, changes in the oxygen isotope values of reservoir fluids provided independent evidence for dissolution of injected CO₂ in the produced waters. It is concluded that geochemical and isotopic monitoring techniques can play an important role in verification of CO₂ storage in mature oilfields and saline aquifers, provided that the isotopic composition of the injected CO₂ is distinct.