Criteria for decision making in site abandonment
Alexander Kronimus, Geert de Bruin, Jens Wollenweber, Vincent Vandeweijer, Rob Arts (all TNO)
Criteria for decision making in the stages of closure and post-closure of CO2 storage sites are related to demonstrate fulfilment of the site conditions that are required for a responsibility transfer from the operator to a competent authority. The high-level criteria are defined in the EU Directive for Storage of Carbon Dioxide 2009/31/EC (EC, 2009):
1) Absence of leakage,
2) Accordance of monitoring data and model predictions,
3) The site is evolving towards long-term stability.
As those criteria are defined on a high level they have to be complemented with risk management criteria allowing to be applied on an operational level. A first set of operational criteria, termed “R-type” criteria, have been extracted from a risk management plan for CO2 storage site responsibility transfer and abandonment developed in Deliverable D4.12 “Risk management plan supporting site abandonment” (CO2CARE, 2013a).
Some criteria therein refer to input from models and monitoring measurements. If a parameter is predicted by modelling and measured by monitoring, high-level criterion (2) stated above is of primary application. For risk management related treatment of observed irregularities in such parameters, a traffic light system with an associated workflow has been set up.
This workflow provides an additional set of criteria (technical or “T-type” criteria), specifically relating to condition (2) of the EU Directive. The major goal of the traffic light system is to provide a framework for dealing with offsets of model predictions and monitoring data (MMO, i.e. Model Monitoring Offset). The three criteria levels (high-level criteria of Directive 2009/31/EC, R-type criteria, T-type criteria) have been connected to each other in order to form a coherent generic set of criteria for transfer of responsibility and abandonment of a CO2 storage site.
The workflow has been thoroughly evaluated on the K12-B site within the preparation of a risk management plan for K12-B (CO2CARE, 2013b).
The practicability of the proposed traffic light workflow could be demonstrated and it is shown how the traffic light system can support the decision making in CO2 storage site responsibility transfer and abandonment by presenting an example of how to deal with unpredicted or irregular behaviour of the storage site. The traffic light system is suitable for treating irregularities through all phases of the storage lifetime.
The approach to define criteria leading to the responsibility transfer of the site revealed that, although based upon a generic framework, the definition of such criteria is highly site dependent. Particularly the definition of tolerable model-monitoring deviations and accuracies/precisions of models is ambiguous and requires thorough considerations by the operator of the site and the Competent Authority.
Although the traffic light system was designed for treating irregularities in the final stages of the storage lifetime it is well applicable to the treatment of irregularities in all stages of a storage project.