oa Field Experiences with Isotopic Tracing of Injected CO2 at Enhanced Oil Recovery Sites in Canada

Monitoring and verification of CO2 storage is an essential component of geological storage projects. We present evidence 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. We conclude 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.