Understanding the risk of leakage if faults and legacy boreholes are present and how to monitor and mitigate against unwanted CO2 migration
The possible expression and rates of leakage along natural and man-made pathways to the surface need to be understood to feed into risk-led site characterisation (e.g. as described in the SiteChar project) and inform monitoring strategies throughout the storage site lifecycle. Previous projects have identified boreholes and geological faults as potential pathways for CO2 to reach the surface.
Few field data are available to ground-truth models on the potential for unwanted migration and leakage of CO2 through boreholes and geological faults in sedimentary basins. Studies of leakage at natural analogue sites were undertaken in the FP7 RISCS project and indicated that further study on the expression of CO2 seepage to the surface through geological faults (vent-focused or diffuse, continuous or sporadic) is required. Currently, examination of the potential for leakage of CO2 through faults mainly relies on modelling studies and laboratory experiments and so field data are required.
An example of rock formations offset by a fault in the UK
The Sotacarbo Fault Laboratory , where CO2 will be injected into or near a fault, offers a rare opportunity to advance understanding of technologies for monitoring CO2 leakage along faults. The activities carried out through ENOS will complement the Sotacarbo Fault Laboratory programme funded by the Sardinia Region and Ministry of Economic Development. Research carried out through ENOS will generate valuable information for development of the most effective surface monitoring strategy for sites where faults are present by providing field data to ground-truth models.
LBr-1 will be used as a case study to produce a best-practice report with recommendations for assessing and mitigating the risks presented by boreholes for future storage sites drawing on lessons learned from a risk assessment prepared for the GETICA site and data on the impact of CO2 on borehole cement.