The answer is to use new technology so that we can collect accurate and cost-effective data. It is then possible to see whether the CO2 stored in the reservoir behaves as expected, says Bahman Bohloli at NGI, Norwegian Geotechnical Institute. He has been the project manager for the EU-funded international research and development project SENSE.
What happens to the ground itself when we pump CO2 into former oil and gas reservoirs under the seabed or on land, that can be used as a storage site? How does the injection of CO2 into such a reservoir affect the surrounding rock formations? And is it possible to predict areas where one should be careful and monitor reservoirs with the stored CO2 for possible leaks?
Five Case Study Sites
In order to find the answers, field studies have been carried out in the sandstone reservoir Hatfield Moors in England, where with the help of satellite data, the connection between pressure changes in the reservoir and movements in the surface has been analyzed.
But what happens over time? In the In Salah CO2 storage in Krechba in Algeria, studies have been carried out on how the surface reacts a few years after the injection has ended.
In addition to the two land-based field studies, offshore field studies have been carried out in Boknis Eck offshore in Kiel in Germany, in the Gulf of Mexico in the USA, and on the Troll field in the North Sea. Using full-scale experiments to measure what is happening on the seabed, and testing of instruments to ensure accurate measurements and calculations of expected movements on the seabed, the industry now has a basis for choosing technology to monitor CO2 reservoirs.
The deformation changes in the ground that must be captured using monitoring equipment are at the millimeter level. However, having to monitor everything would be too expensive and demanding a task.
“Therefore, it has been important to understand more about how CO2 behaves in the reservoirs, and how the rocks that surround the reservoirs affect the possibilities of leaks,” says Bohloli.
Easy to monitor and ensure safe CO2 storage
He concludes that it is now relatively easy to monitor CO2 reservoirs and thus ensure safe storage. The use of satellites (InSAR measurements) on land and fiber optic cables on the seabed makes it possible to monitor CO2 reservoirs cost-effectively.
“Yes, in SENSE, researchers and industry players have jointly developed tools and methods to record and measure swelling in the ground or on the seabed above where the CO2 is stored. Based on these registrations, we have developed geomechanical models. This gives us information about how the CO2 will behave in the storage reservoir, and how tight (impermeable) the reservoirs are. Should there be a leak, which results in the ground surface rising to a millimeter level, the alarm will go off,” says Bohloli.