Fact box 6.4 - Principles for injecting CO2

An aquifer may comprise several sedimentary formations and cover a large area.

Its rocks must have good porosity and permeability, where water in the pores is in communication. To be suitable for storage, the formations must be at a depth where CO₂ can be held in a super-critical phase (figure 6.10 [26]).

They must be covered by a thick cap of claystone and shale, forming a seal which prevents the CO₂ from migrating to other formations or the seabed. While gaseous under atmospheric pressure, CO₂ will behave as a liquid under the increased pressure and temperature at depths beyond about 800 metres.

 

Figure 6.10 Principles for CO2 storage. Source: NPD (2014).