3.1.1 Monitoring guidelines according to EU CCS Directive and related Guidance Documents

According to the EU CCS Directive monitoring is essential to assess:

  • whether injected CO2 is behaving as expected,
  • whether any migration or leakage occurs, and
  • whether any identified leakage is damaging the environment or human health.

For this, the operator is required to monitor the storage complex and the injection facilities on the basis of a monitoring plan. The operator needs to report the results of the monitoring to the competent authority at least once a year. In addition, Member States are required to establish a system of inspections to ensure that the storage site is operated in compliance with the requirements of the EU CCS Directive. Detailed monitoring guidelines based on EU CCS Directive requirements are available in the Guidance Document 2 (2011) "Implementation of Directive 2009/31/EC on the Geological Storage of Carbon Dioxide. Guidance Document 2. Characterisation of the storage Complex, CO2 Stream Composition, Monitoring and Corrective measures".

According to the EU CCSs Directive (Article 13, Annex II and other articles) monitoring of injection tests may be included in the exploration permit. Applications to the competent authority for storage permits shall include a proposed monitoring plan including details on the monitoring in accordance with the guidelines established by Article 14 and Article 23(2) of the EU ETS Directive 2003/87/EC. The plan shall be updated in any case every five years to take account of changes to the assessed risk of leakage, changes to the assessed risks to the environment and human health, new scientific knowledge, and improvements in best available technology.

The monitoring plan shall be established according to the risk analysis and updated with the purpose of meeting the monitoring requirements at the different CO2 storage project phases. The established monitoring plan shall provide details of the monitoring to be deployed at the main stages of the project, including baseline, operational and post-closure monitoring. The following features shall be specified for each phase:

  • parameters monitored;
  • monitoring technology employed and justification for technology choice;
  • monitoring locations and spatial sampling rationale;
  • frequency of application and temporal sampling rationale.

The parameters to be monitored will be identified as to fulfil the monitoring purposes. The monitoring plan shall in any case include continuous or intermittent monitoring of the following items:

  • Fugitive emissions of CO2 at the injection facility;
  • CO2 volumetric flow at injection wellheads;
  • CO2 pressure and temperature at injection wellheads (to determine mass flow);
  • chemical analysis of the injected material;
  • reservoir temperature and pressure (to determine CO2 phase behaviour and state).

The choice of monitoring technology shall be based on best practice available at the time of design. The following options shall be considered and used as appropriate:

  • technologies that can detect the presence, location and migration paths of CO2 in the subsurface and at surface;
  • technologies that provide information about pressure-volume behaviour and areal/vertical distribution of CO2 plume to refine numerical 3D simulation to the 3D-geological models of the storage formation;
  • technologies that can provide a wide areal coverage in order to capture information on any previously undetected potential leakage pathways across the areal dimensions of the complete storage complex and beyond, in the event of significant irregularities or migration of CO2 out of the storage complex.

The monitoring data shall be collated and interpreted. The observed results shall be compared with the behaviour predicted in dynamic simulation of the 3D-pressure-volume and saturation behaviour undertaken in the context of the safety characterisation. Where there is a significant deviation between the observed and the predicted behaviour, the 3D model needs to be recalibrated to reflect the observed behaviour. Where new CO2 Sources, pathways and flux rates or observed significant deviations from previous assessments are identified as a result of history matching and model recalibration, the monitoring plan shall be updated accordingly.

After a storage site has been closed, the operator remains responsible, amongst other things, for monitoring (post-closure period). After the transfer of responsibility, monitoring should be reduced to a level which still allows for identification of leakages or significant irregularities, and it should again be intensified if leakages or significant irregularities are identified.