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Leakage Detection

In line with the CCS Directive, any CCS storage complex monitoring strategy needs to assess whether any migration or leakage or CO2 is occurring within the surrounding area. Such strategies need to accommodate the fact that CO2 leakage may occur from a single point source or as more diffuse discharge over a larger area, and similarly that the leaking CO2 may be present in form of CO2 gas bubbles or dissolved into the interstitial waters of the sediments and overlying water column. Given these complexities, a number of different methods and techniques for detecting CO2 leakage under varying scenarios were tested through the STEMM-CCS project, with their relative performance and individual merits summarised below.

User Guide

The techniques and technologies developed and tested during the STEMM-CCS project that are relevant to this monitoring task are shown in the bar chart below. This chart indicates the overall ‘suitability score’ for each approach, which reflects an averaged ranking of each approach against 5 monitoring parameters: (1) Time needed to obtain the final results; (2) Cost of the measurement; (3) Spatial extent of detection covered by the method; (4) The relative CO2 leakage rate and nature of leakage (i.e. bubbles or dissolved) that can be detected; (5) Technical readiness level of the method. Scores are provided on a scale from 1 to 3 and depend on many external factors, thus are defined relative to each other based on the scientific expertise of STEMM-CCS partners, using information available as of February 2020.

A description of the functionality of each technique and technology, an image of the associated instruments, a data example acquired during the STEMM-CCS project or another relevant project, and a summary of the strengths and limitations are made visible by clicking on the method of interest within the bar chart (which goes dark blue when selected). A breakdown of how the method was rated against the 5 monitoring parameters is provided in the ‘method scoring’ table, and is summarised in the spider diagram.

A direct comparison of the relative effectiveness of different methods can be viewed using the ‘comparison mode’, which is enabled by clicking on the box at the top of the bar chart. Within this function, multiple methods can be selected and compared (click on all techniques/technologies of interest), with the parameter scores for each approach summarised in a comparison table. The order in which the methods are ranked can be adjusted by selecting the parameter name within the table heading; an arrow will appear within the header to indicate the active selection. Recommendations on how to apply each of the selected methods are provided below the comparison table.

Monitoring Methods

Recommended Measurement

Irrespective of the monitoring method(s) chosen, a variety of additional measurements are recommended to be conducted before, during, and after the injection of CO2 in order to support the successful delivery of this monitoring task. These measurement needs are indicated below, with further information on each of the suggested approaches visible by clicking on the measurement types titles.

MeasurementPre-InjectionDuring OperationPost-Injection
Overburden and seabed characteristics Recommended--
Potential leakage pathways in overburden Recommended--
Seabed chemical characteristics Recommended Recommended Recommended
Water column physical properties Recommended Recommended Recommended
Water column carbonate system characteristics Recommended Recommended Recommended
Water column chemical and biology parameters Recommended Recommended Recommended
(Recommended measurement detail)