Introduction to Geological Sequestration - Introduction to Carbon Capture and Sequestration - page 363

100

Structural and
stratigraphic
trapping

80

60

Increased storage securiy

Residual CO 2
trapping

40

Solubility
trapping 20

Mineral
trapping

0

1 10 100 1000 10,000

Time since injection stops (years)

Figure 8.2.3 Trapping mechanisms as a function of time
Figure adapted from Benson and Cole [8.3].

these cations then become available to react with CO 3 2 − in the aque-
ous phase to form carbonate minerals. As carbonates are the thermo-
dynamically most stable form of carbon, mineral trapping is the fi nal
fate of our injected CO 2 . You may have noticed that the chemistry of
CO 2 sequestration presented here (CO 2 dissolution in water, the
weathering of silicate minerals, and the eventual formation of carbon-
ate minerals) is the same as the chemistry of the natural CO 2 cycle
discussed in Sections 3.3 and 3.4.
The sequential trapping mechanisms are illustrated in Figure 8.2.2. It
is important to realize that each of these mechanisms has its own time
scale. For example, mineralization may take thousands of years. Another
important point is that for each subsequent step in this trapping
sequence, it becomes increasingly diffi cult for CO 2 to escape, and hence
the likelihood of the CO 2 escaping decreases as time goes on [8.3]. This
evolution of the storage security is illustrated in Figure 8.2.3. In the next
chapter, we will discuss the physics and the time scales associated with
these mechanisms in more detail.