Fingerprinting Captured CO2 Using Natural Tracers for CCS Monitoring and Verification

Abstract:

In the long term, captured CO₂ will most likely be stored in large saline formations and it is highly likely that CO₂ from multiple operators will be injected into a single saline formation. Understanding CO₂ behaviour within the reservoir is vital for making operational decisions and often uses geochemical techniques. Furthermore, in the event of a CO₂ leak, being able to identify the owner of the CO₂ is of vital importance in terms of liability and remediation. Addition of geochemical tracers to the CO₂ stream is an effective way of tagging the CO₂ from different operators, but may become prohibitively expensive at large scale storage sites. Here we present results from a project assessing whether the natural isotopic composition (C, O and noble gas isotopes) of captured CO₂ is sufficient to distinguish CO₂ captured using different technologies and from different fuel sources from each other and from likely baseline conditions.

Results include analytical measurements of CO₂ sampled from a number of different CO₂ capture plants and a comprehensive literature review of the known and hypothetical isotopic compositions of captured CO₂ and baseline conditions.

Key findings from the literature review suggest that the carbon isotope composition will be most strongly controlled by that of the feedstock, but significant fractionation is possible during the capture process; oxygen isotopes are likely to be controlled by the isotopic composition of any water used in either the industrial process or the capture technology; and noble gases concentrations will likely be controlled by the capture technique employed. Preliminary analytical results are in agreement with these predictions.

Comparison with summaries of likely storage reservoir baseline data and shallow or surface leakage reservoir baseline data suggests that C-isotopes are likely to be valuable tracers of CO₂ in the storage reservoir, while noble gases may be particularly valuable as tracers of potential leakage.