CO Capture and Storage - Energy and Climate: How to Achieve a Successful Energy Transition - page 110

reduce the CO 2 solubility, leading to massive release of CO 2 . For all these
reasons, this option is not considered as acceptable by the European
Union.
Underground geological storage is therefore the solution generally
favoured. Numerous natural underground CO 2 reservoirs already exist
in different regions of the world. Such storage is based upon the fact
that sedimentary rocks are, in general, porous. Sandstone, which is
formed by agglomerated sand particles, is a good example of such
sedimentary rocks. The rock porosity is generally filled by water
(salt aquifer). Carbon dioxide is injected through awell in the sedimentary
rock and forces out the water. Using such a porous layer as an under-
ground reservoir also requires the presence of a cap rock above
the sedimentary layer, which acts as a seal preventing upward migration
of CO 2 .
The main possible options for CO 2 underground storage are illustrated
in Figure 8.1. Captured CO 2 can be stored in depleted oil and gas fields,
deep saline aquifers and unexploited coal seams.

Figure 8.1 Carbon dioxide underground storage modes ( Source : IFP-

Energie &Climat: Reussir

ADEME-BRGM [90]). Reproduced with permission from

by Alexandre Rojey, ´ ditions Technip, Paris, 2008 la transition energetique