What does CO2 geological storage really mean?

The information in these pages is an update of the CO2GeoNet brochure first published in 2008, and translated into 31 languages.

Where and how much CO2 can we store underground?

CO2 cannot be injected just anywhere underground; firstly suitable host rock formations must be identified. Potential reservoirs for CO2 geological storage exist throughout the World and offer sufficient storage capacity to make a significant contribution to mitigating climate change. Two main storage options exist for CO2 (Fig. 5):

1.Depleted natural gas and oil fields –well known due to hydrocarbon exploration and exploitation, offer immediate opportunities for CO2 storage;

2.Deep Saline aquifers –offer a larger storage potential, but are generally not as well known.

In addition, unmineable unmineable coal seams and volcanic and other igneous rocks may offer regional storage capacity.


How can we transport and inject large quantities of CO2?

After its capture at the industrial facility, the CO2 is compressed, transported, and then injected into the reservoir formation through one or several wells. The whole chain has to be optimized to enable the storage of several millions of tons of CO2 per year.

What happens to the CO2 once in the storage reservoir?

Once the CO2 is injected in the reservoir, the CO2 will rise buoyantly filling the pore spaces below the cap rock. Over time, part of the CO2 will dissolve and eventually be transformed into minerals. These processes take place at different time scales and contribute to permanent trapping.

Could CO2 leak from the reservoir and, if so, what might be the consequences?

Based on the study of natural systems, carefully chosen storage sites are not expected to show any significant leakage. Natural reservoirs containing gas help us to understand the conditions under which gas is trapped or released. In addition, natural seepage sites help us recognise what the possible impacts of CO2 leakage could be.

How can we monitor the storage at depth and at the surface?

All CO2 storage sites will need to be monitored for operational, safety, environmental, societal and economic reasons. A strategy has to be drawn up to define what exactly will be monitored and how.

What safety criteria need to be imposed and respected?

In order to ensure storage security and efficiency, conditions for project design and operation must be imposed by the regulating authorities and respected by the operators.