Monitoring and CO2 accounting

identified challenges

• Present monitoring technologies
• Accuracy and detection limits
• Durability and maintenance
• Cost
• Develop new monitoring and detection technologies
• Establish a library containing strengths and limitations for the different technologies and how they may complement each other.

The CO₂ used for EOR is by the US government considered permanently stored, assuming no leakage. In the same manner the CO₂ injected at Sleipner is not accounted for in the Norwegian greenhouse gas inventory. In the certification of a CCS site it will be important, in view of Emission Trading and for reporting emissions to the UNFCC, to account for the amount of CO₂ stored. In such context it is also important to estimate, as accurate as possible, the volume of CO₂ migrating out of the formation. It is usually distinguished between migration and leakage. A migration is CO₂ moving out of the reservoir it is injected into. If such a migration reaches the atmosphere or the ocean it is labelled a leakage.

It will important to quantify the CO₂ reaching the atmosphere, lakes or the ocean. A continuous leakage will not only have potentially local ecological consequences, it will also be an issue for the trading of quotas and reduce the benefit of storage. It will introduce a new source for CO₂ that have to be accounted for in the global carbon-dioxide budget. In this context, the ocean, presently being a major sink of atmospheric CO₂, might serve as a buffer. Depending on the depth of the leakage, the CO₂ might stay in the ocean for decades or centuries.

Each CO₂ storage project will have to develop an adequate and unique monitoring program that will have to fulfil two main criteria; demonstrate that the reservoir performance meets the defined standards, yet to be established, and assure that migration or leakage does not occur, and if it occurs detect and quantify the rates of the migration. The monitoring program should last for years into the post-injection period and might have to cover an area of 100 km². Hence reliable and durable instrumentation will have to be developed.  Cost of the instrumentations is another issue.