Risk Management in the context of closing and abandoning a CO2 storage site encompasses all the measures required to demonstrate the long-term safety of a CO2 storage site. The latter represents a pre-condition to transfer the responsibility for the abandoned site from the operator to the Competent Authority (CA) on a national level.
The aim of this study was to establish a corresponding risk management plan covering the requirements of the EC Directive on the geological storage of carbon dioxide (DIRECTIVE 2009/31/EC) and the OSPAR Guidelines. The timeline considered by this plan encompasses the final injection period within the operational phase as well as the post-closure/pre-transfer and post-transfer period of a storage project.
Before such a transfer can be approved it is required that
a) all available evidence indicates that the stored CO2 will be completely and permanently contained,
b) the financial obligations have been fulfilled,
c) the site has been sealed and the injection facilities have been removed.
Before the transfer of responsibility can be approved by the CA, the operator has to demonstrate
a) the conformity of the actual behaviour of the injected CO2 with the modelled behaviour,
b) the absence of any detectable leakage,
c) the storage site is evolving towards a situation of long-term stability.
Within this study a milestone chart in accordance to given EC regulations has been developed to facilitate an industrially applicable procedure for risk management measures in the context of responsibility transfer and abandonment of a CO2 storage site. The chart consists of 17 milestones, which have been specifically allocated to the different phases and sub-phases of the timeline of CO2 storage site, specifically during the final operational and post-closure phases. The developed milestone chart has been evaluated for the K12-B CO2 injection site, the findings of which have been used for updating the milestone chart.
Monitoring is an essential element in risk management, also in the post-operational phase. Appropriate site-specific monitoring measures are to be set up during the licensing procedure for a CO2-storage site, which establishes the starting-point for demonstrating how the requirements for the transfer of responsibility can be met.
DIRECTIVE 2009/31/EC and its Guidance Documents (GD) propose minimum periods to fulfil certain key criteria, which are not based on any scientific fundament, such as:
- a default period of 20 years after site closure for the transfer of responsibility for a CO2 storage site; this time span can be reduced, if the long-term safety of the site could be sufficiently proven in a shorter period (DIRECTIVE),
- a minimum period of absence of leakage of 10 years immediately before the time of transfer (GD),
- for at least 5 years before the transfer, the 3D static geological model does not need any significant update (GD),
- the monitoring plan shall be updated in any case every 5 years (DIRECTIVE).
It is recommended that the decision if a criterion for the safety of a site has been met should be based on technical aspects only and should not be linked to prescriptive time spans.
Instead, a post-operational CO2 storage site should be sealed as soon as possible after all criteria for the transfer have been fulfilled and the Competent Authority is convinced of the long-term integrity of the storage site. The definition of criteria for responsibility transfer and abandonment are included in a separate CO2CARE document.