There are some misconceptions about storage site monitoring. It’s commonly believed that because there are a lot of potential monitoring tools out there, they will all have a part to play as CCS is rolled out. The abundant use of monitoring tools in pilot-scale projects has also perhaps left the impression that costs of monitoring tools are low, so they are barely a cost consideration. This is not necessarily the case.  

In fact, future industrial-scale storage monitoring programmes are likely to be fairly simple with a limited portfolio of tools deployed. Industries are likely to look for the cost-optimal mix of techniques that meets site-specific requirements imposed by regulators.

To decide which techniques are to be used, we need to know what monitoring has to show. The European Union Directive on the geological storage of carbon dioxide leaves us with four main requirements: we have to demonstrate that the site is working as expected, that we understand current processes and can make reliable predictions of future ones, that there is no evidence of leakage, and that operations will be safe to people and the environment. 

Most of this concerns the deep underground, so deep-focussed monitoring systems will be the principal means of ensuring that the legal requirements are met. Here, the optimising starts. At industrial-scale storage sites, existing wells are typically several kilometres apart with wellbores difficult or costly to access. New surveillance wells are very expensive. Therefore, deep-focussed monitoring is likely to comprise a judicious combination of down-hole and surface technologies.

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Source: Global CCS Institute - Blogs - Andy Cadwick 14. Dec. 2011