State-of-the-Art of Monitoring Methods to evaluate Storage Site Performance

 
1. INTRODUCTION
 
2. MONITORING TECHNIQUES
 
3. MONITORING CONCEPTS – STATUS QUO
 
4. SETTING UP A SITE-SPECIFIC MONITORING PLAN
 
5. CONCLUSIONS AND RECOMMENDATIONS
 
6. REFERENCES
 
 
» 4.1 Mapping of relevant areas
 
4.2 Definition of monitoring objectives and intensity
 
4.3 Selection of methods and specification of measurements
 
4.4 Examples
 
 

4.1 Mapping of relevant areas

The EU CCS Directive requires that the storage site operator monitors the injection facilities, the storage complex and, where appropriate, the surrounding environment and carries out comparisons between modelled and actual behaviour of CO2 and formation water. All Hydraulic units in sequences above or around the storage site that might be connected directly, through connected fractures or caprock failure to the CO2 reservoir must be mapped and relevant areas for monitoring and observation must be defined. If CO2 migrates via faults into porous and permeable reservoir rocks outside the storage site, it may be transported to the surface several kilometres away from the storage site and result in CO2 emissions.

Monitoring should cover the storage complex and, when appropriate, the surrounding environment to ensure that leakage through other aquifer systems or fracture networks is observed and related to the storage site. It is important to identify and map structural trends, possible leakage pathways (e.g. faults, fracture networks) and shallower aquifer systems to identify the critical areas for monitoring and to reduce the acreage and cost of monitoring.

In addition to naturally occurring pathways for CO2, all possible existing and planned manmade pathways including wells and boreholes, which could provide leakage routes, must be identified and considered for monitoring. Abandoned and existing boreholes and wells ‑ both deep hydrocarbon wells and shallower water wells, mines, tunnels and constructions that may have damaged or intersected the caprock of the CO2 reservoir or shallower hydraulic systems can be potential leakage pathways for CO2.

Furthermore, the ownership and borders of commercial and residential areas, recreational and nature reserve areas at the surface must be established and legal rights, obligations and restrictions to perform monitoring must be made clear.

The type of monitoring equipment and its use must be selected to avoid conflicts. Nevertheless, it should still be sufficient and adequate to observe the behaviour of CO2 in the subsurface and to detect signs of potential leakage at an early stage, so as to enable mitigation and limit possible damage to the environment and human health. In addition to hse and operational monitoring, the ets monitoring requirements need to be considered. This may result in employment of additional monitoring tools, enabling the quantification of a potential leakage.