Capture and geological storage of CO2

The geological storage of CO2

Part of the CO2 captured during the CCS process can be valorised by the food-processing and chemicals industries. However, these outlets use far less than the quantities of CO2 that are potentially recoverable from industrial sites. Hence the need for storage.

The best storage solution is geological: injection of the CO2 into layers of permeable rock lying underneath gastight layers that will prevent the CO2 from escaping. The storage reservoirs must be far enough underground to allow the CO2 to reach a quasi liquid state and so occupy as little space as possible.

Most of the suitable storage sites are end-of-life oil and gas fields, deep saline aquifers (porous rock layers at great depth impregnated with salt water) and – to a lesser extent – coal beds that are too deep to be mined. >> (Find out more: Different types of storage)



The IPCC estimates that the combined estimated storage capacity of all suitable sites worldwide is between 1,000 and 10,000 billion tonnes of CO2 (this figure includes depleted oil/gas reservoirs and saline aquifers). In comparison, annual emissions of CO2 due to human activity amount to about 30 billion tonnes.Efforts are currently underway to take an inventory of and evaluate geological storage sites in different States throughout the world.


Did you know?

The Earth has natural deposits of CO2. Some of these reservoirs have been produced to meet the needs of the food-processing industry (gaseous mineral water, for example) among others. This gas is also used by the oil and gas industry: CO2 is injected into mature reservoirs to stimulate production. In this technique, called Enhanced Oil Recovery, the CO2 makes the oil less viscous and easier to extract.

Find out more: Different types of storage

Storage in depleted oil and gas reservoirs

These sites have number of advantages, but the most important one is that they are well known and documented. They are natural reservoirs that have demonstrated their ability to contain hydrocarbons for periods of several million years.

In addition, oil and gas companies are skilled at extracting and injecting fluids from and into deep reservoirs. CO2 has been injected into reservoirs like this for some time (as part of the Enhanced Oil Recovery process) and the technique has now been mastered.

Another advantage of using these reservoirs is that some of the infrastructure already used for oil/gas exploration and production (wells, pipelines, etc.) can be used again for CO2 storage, thus reducing the cost.

On the other hand, these reservoirs are not always located near the plants that generate the CO2, and so the truly available storage capacity may not be enough to cover the needs.

Storage in saline aquifers

The are numerous saline aquifers in the Earth’s sedimentary basins, and individual aquifers can cover areas of several thousand square kilometers. They may be located onshore or offshore. These aquifers are made up of porous and permeable rock that is often impregnated with water so salty as to be unfit for consumption. When the aquifers are deep enough (> 800 m underground) and lying beneath impermeable “cap” layers they can be used to store large amounts of CO2. However, there is still a lot of work to be done before we have a good understanding of these geological structures.

Storage in coal beds that are too deep to be mined

In the case of coal storage, the CO2 is absorbed by the coal itself, but this solution is only feasible where the coal deposit is covered by impermeable gastight layers so that the CO2 can be kept underground and the coal methane can be recovered (a technique called Enhanced Coal Bed Methane Recovery). Here again, much work needs to be done to evaluate this potential solution.
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