6.2.2 Monitoring

Monitoring information is very relevant for providing an overview on the operational history of a site and therefore to evaluate its impact on well abandonment. Particularly real data on pressure, chemistry and plume behaviour are essential for any risk assessment of the storage area and penetrating wells. Therefore, an appropriate risk-based monitoring plan is already required as part of any site authorisation. The proposed monitoring plans will be reassessed based on available models and monitoring data during the injection phase and an adapted post-injection monitoring plan will need to be resubmitted to the relevant authority. Because there are a many different storage-sites, the requirements on monitoring plans should always be site-specific. However, to achieve at least some consistency the regulations should state objectives and performance standards rather than specific techniques to be applied. This allows for new techniques to be applied.

In General, considering EU CCS Directive 2009/31/EC and WRI Guidelines, the monitoring plan should consider:

  • Site specificity, plans to take site characteristics into account.
  • Monitoring plans according to site characterisation and risk assessment. High risk areas would require more heavily monitoring.
  • sufficient extension of monitoring area (cover plume and surrounding environment)
  • preventive/corrective measures (monitoring to ensure their effectiveness)
  • best practice technology, flexibility to keep up with advancing technologies
  • required frequency for the defined technique and regular/routine reporting and interpretation of data
  • Flexibility, update monitoring according to changes in risks, technology, etc.
  • Baseline monitoring to make inferences with monitoring
  • Possible change in monitoring frequency after cessation of injection
  • Possible monitoring for the time after the liability-transfer. Liability transfer demands the demonstration of site safety, but maybe low level monitoring should be considered to confirm this.

There is a wide range of monitoring options respective parameters to be monitored according to the decided site-technique. A short guide is taken from CO2Care D 1.2(Wollenweber, 2012) and lists the following:

  1. Injection well parameters:
    • Injection rate
    • Pressure and temperature at well head
    • Chemical analysis of injected material
    • Volume of injected CO2
    • Formation pressure and temperature
  2. Well performance and integrity
    • Mechanical integrity
    • Corrosion monitoring of well
  3. Pressure fall of testing. Designed to determine if reservoir pressures are tracking predicted pressures and modelling inputs
  4. Monitoring well parameters (confining zone and above)
    • Pressure and temperature data
    • CO2 saturation
    • Geochemical data
  5. Geophysical images of the plume
    • Seismic
    • Electrical surveys
    • Microgravity
  6. Surface deformation -> information on CO2 plume
  7. Surface detection
    • Groundwater samples
    • Soil-gas surveys

All monitoring plans must be chosen according to the particular risks of the project. The decision on spatial/temporal monitoring frequency for satisfactory results should of course be site-specific. Seismic monitoring surveys are cost intensive, but should provide at least the cover of the CO2 plume. The number and position of monitoring wells and surface monitoring station should be based on the individual risk assessment of the project and is therefore within the responsibility of the authorities. Indirect methods used for monitoring require adequate knowledge about the relation between measured quantity and CO2. The main factor for deciding on monitoring techniques is the cost/benefit ratio. Low cost - high benefit monitoring will definitely be used, whereas high cost - low benefit tools are unlikely to be used unless they are considered vital.