Monitoring Principles for CCS Wells

Permanent storage of carbon captured from industrial processes is necessary to achieve the long-term temperature goals of the Paris Agreement (e.g., [1]). Adequate revenue allocation to parties in the Carbon Capture and Storage (CCS) value chain requires accurate measurement and monitoring throughout. Particularly, measurements of the CO₂ stored are key to correctly associating carbon credits to capture sites. Ensuring long-term containment in the storage facility, raising the public acceptance of CCS, and proving sustainability, encompass demonstration that the captured CO₂ is safely transported and stored [2]. For this purpose, the development of trustworthy monitoring of transport, injection infrastructure, and storage sites is crucial. Measurement techniques and monitoring frequency are not constant throughout the project life, and individual storage sites pose different challenges and opportunities [1]. Monitoring plans should, hence, be developed from the site-specific conditions and will thus be different for different projects. The present work results from an effort to provide a general overview of technologies that can aid in ensuring conformance-, containment-, and contingency monitoring. Best practice procedures and openly available literature, in hand with technical specifications from suppliers, are used to benchmark technologies that could meet well-monitoring needs. Such needs comprise verification that the injected CO₂ travels and behaves as predicted, ensuring there are no leakages from the injection facility or storage site, and detecting potential threats to future containment of CO₂. The work also considers lessons learned from various carbon sequestration projects, like the Sleipner and Snøhvit fields in Norway and the Quest CCS facility in Canada. The manuscript assesses the feasibility of different well-monitoring techniques encompassing injection, well integrity, bottom hole conditions, and CO₂ plume migration. To know the inventory of the storage formation, injection monitoring at or near the wellhead is required. Such monitoring encompasses temperature, pressure, density, composition, and mass flow. Of these, emphasis is placed on mass flow measurement and inline composition analyses for having a lower technology readiness level (TRL) for CCS, compared to the three former-mentioned monitoring needs. Regarding well integrity, the potential of a number of commercially available technologies to ensure containment and contingency are assessed. The focus is on monitoring the quality of the steel casing and the surrounding cement, and the bondage between them. Further, to ensure long-term storage of CO₂, it is essential to monitor the CO₂-plume in the storage formation. In the geosphere, a solid baseline measurement must be made prior to injection, against which changes stemming from the injected CO₂ are compared. Monitoring of the CO₂-plume thus encompasses active and passive methods, i.e., monitoring the development of the plume perse and detection of seismic activities in the storage site. Overall, the work assesses 20 technologies, covering injection-, well integrity-, bottom hole-, and CO₂-plume monitoring. The technologies are benchmarked against three criteria: Performance for conformance monitoring, performance to monitor leakages, and potential to indicate future contingency threats. The methods are evaluated using a qualitative three-level scale. To be categorised as good, the technology must provide high-quality data for the target in question, or there must be a development that aims to reach such a level for non-mature technologies. Intermediate performance means that useful information can be achieved for the monitoring target. Altogether, the criteria and scores rate the expected performance of the technology for the measurement of CCS streams. Finally, an evaluation of TRL is included to illustrate how far from utilisation the given technologies are.