A pertinent example is the selection of sites for the storage of carbon dioxide within geological strata, which is one option within the broader portfolio of techniques being considered worldwide to help meet greenhouse gas emissions targets. Geological carbon dioxide storage sites range from deep saline aquifers to depleted hydrocarbon reservoirs.

During the process of site selection for carbon dioxide storage, early phases will typically involve consideration of a number of sites with different qualities and, often, limited data that is directly relevant to making judgements on suitability for long-term carbon dioxide storage. A decision needs to be taken on the number of candidate sites to be taken forward for characterisation. Later this small number will need to be narrowed down to those taken forward for implementation. Early phases of site selection processes will involve limited data and substantial uncertainty. Decisions need to be taken that are based upon the best prospects for successful implementation given this uncertainty.

The technique of Evidence Support Logic (ESL) is designed to assist decision-makers when faced with complexity and uncertainty. Through the development of a decision-tree capturing the decision logic, and through the independent evaluation of evidence ‘for’ and ‘against’ the elements of that decision tree, an understanding can be gained of the nature and significance of remaining uncertainty. This allows an assessment of, for example:

• The balance of confidence in favour of particular sites, given remaining uncertainty;
• The likelihood that uncertainties could be resolved with cost-efficient characterisation, leading to a step-change in confidence.

The presentation and analysis tools embedded in TESLA offer significant help in this regard. ESL studies have proven very cost effective given the benefits gained for such major investment projects. James et al (2010) and Tucker et al (2013) provide examples of the use of ESL for major CCS projects. These typically look at the key elements of Capacity; Injectivity; Containment; and Monitoring (see Figure below).

Specifically for ‘Containment’, Quintessa has been involved in developing carbon storage site assessment and integration tools for the CO2ReMoVe project (Metcalfe et al., 2013). The Figure below shows a high-level view of the ‘standard’ ESL decision tree developed to reflect the requirements of the EC Directive (EC, 2009) on carbon dioxide geological storage. The ‘template’ has been parameterised to show an example containment assessment application for a hypothetical site with limited data. This shows the limited data is in favour of performance but highlights areas of uncertainty to be resolved in the future. Metcalfe et al (2013) describes a different type of assessment utilising the same standard tree, considering a substantial data set from the In Salah demonstration site in Algeria.

European Parliament and Council of the European Union (EC), 2009. Directive 2009/31/EC of the EC of 23 April 2009 on the Geological Storage of Carbon Dioxide.

James, S, Garnett, A, Kumar, G, Kumar, V, Rao, N, Trivedi, B, Gupta, A, Salunka, S, Sarakar, S, Scrinivasan, A, Meen, P, Doran, S, Hall, N, and Barlar, P, 2010. What does it take to evaluate a potential CO₂ Storage Site? The ZeroGen example. Proceedings of the Abu Dhabi International Petroleum Exhibition and Conference, UAE 1-4 November 2010. Society of Petroleum Engineers Reference SPE 137447.

Metcalfe R, Paulley A, Suckling PM, and Watson CE. 2013. A tool for integrating and communicating performance-relevant information in CO₂ storage projects: description and application to In Salah. Energy Procedia 37 (2013) 4741 – 4748.

Tucker O, Holley M, Metcalfe R, Hurst S. 2013. Containment risk management for CO2 storage in the Goldeneye depleted gas field, UK North Sea. Energy Procedia 37 (2013) 4804 – 4817.

Link image courtesy of and copyright of CO2CRC.