Isotopic Tracers as Monitoring Tools for CO2 Sequestration  

Authors / CoAuthors

Stalker, L. | Boreham, C.J. | Perkins, E.

Abstract

There are numerous isotopic tracers that have the potential to track the movement of CO2 as it is sequestered underground. Their primary role is in verifying the presence of sequestered CO2. These tracers range from CO2 to 3He to PFT?s to SF6. With such a variety of possible tracers, it is important to identify which tracer(s) are (a) economically viable, (b) can be measured appropriately, (c) fit with the specifics of the geological site, and (d) meet the concerns of the public. Tracers can be used either in a continuous mix with the whole body of sequestered gas as an ownership label or in a pulse to monitor changes in the reservoir characteristics of the body of rock hosting the sequestered gas. Rather than going to the expense of adding a tracer to the stream of sequestered CO2 there may be the opportunity to use natural tracers, such as the very CO2 being injected. In the Weyburn Project, the CO2 injected was isotopically distinct from any CO2 that might have been present in the geological system to which it was being added. The CO2 piped from a gasification plant in North Dakota had an isotopic signature quite depleted in 13C (approx. ?13C -20 to -30?; ref Hirsche et al., 2004). This contrasted with the carbonate minerals and any CO2 present in the hydrocarbon reservoir to which the gas was being sequestered as part of an enhanced oil recovery (EOR) project. Unfortunately, the sequestered CO2 may not be as isotopically different as background sources, for example separating CO2 from natural gas prior to re-injection in the same formation. Costs of tracers per litre can range in orders of magnitude; however the cost should be measured as amount per metric tonne CO2 in order to obtain the true cost. Amounts required tend to be controlled by the background atmospheric presence of any tracer and by the sampling methods and locations. For example, the amount of tracer used to monitor subsurface movement of CO2 from an injection to a monitoring well would potentially be very low if that tracer is not present in deep saline aquifers. However, if shallow water bores or soil or atmospheric level measurements are also being taken, then the presence of the tracer in the soil or atmosphere will strongly control how much additional tracer is required to see changes above background. Addition of 14CO2 to sequestered CO2 may be regarded as a cost effective tracer that will closely mimic CO2. However, it will not advance ahead of the sequestered CO2, it will mask natural differences in 13C/14C variations in the soil and atmosphere, and of course is radiogenic and therefore less favored by the public. By contrast, SF6 (sulphur hexafluoride) is also inexpensive, and has been used in a variety of tracer experiments (Tingey et al., 2000 and references therein). However, SF6 is required in larger volumes (engineering issue for mixing), is increasing in presence in the atmosphere (Maiss and Brenninkmeijer, 1998) and is a highly potent greenhouse gas. As an example of its global warming potential (GWP), 5500 tonnes SF6 is the equivalent of releasing 132 million tons of CO2 (Maiss and Brenninkmeijer, 1998).

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nonGeographicDataset

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61877

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• External PublicationAbstract

( Theme )

• CO2 capture

( Theme )

• carbon dioxide

( Theme )

• geochemistry

( Theme )

• organic geochemistry

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

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2005-01-01T00:00:00

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Australian Government Security ClassificationSystem    

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Creative Commons Attribution 4.0 International Licence    

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geoscientificInformation

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Extended Abstract for 6th International Conference for Applied Isotope Geochemistry, Prague

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