Large-Scale Geological Carbon Sequestration - Introduction to Carbon Capture and Sequestration - page 478

geochemistry of very thin adsorbed water fi lms may differ from that of
bulk liquid water. One of the few existing studies of the geochemical
impact of these fi lms showed that the weathering reaction of the mineral
forsterite (Mg 2 SiO 4 ) by supercritical CO 2 in the presence of an adsorbed
water fi lm resulted in CO 2 mineral trapping as magnesite (MgCO 3 ) on a
time scale of weeks [10.28]. This result is remarkable, because the pre-
cipitation of magnesite in bulk liquid water in the same conditions is too
slow to detect in the laboratory. This difference suggests that the very
slow desolvation of Mg 2 + (thought to be the rate-limiting step of magne-
site precipitation) occurs more rapidly in an adsorbed water fi lm than in
bulk liquid water.
Section 3
Capacity assessment
Having discussed above the continuum scale aspects of the rock forma-
tions, their structures, pore-space properties, and two-phase fl ow pro-
cesses, we are in a position to consider the larger-scale question of how
much CO 2 can be reasonably expected to be injected and stored in suit-
able geological formations. This question turns out to be quite compli-
cated, and as there is a lack of experimental data from actual large-scale
injections, it is the subject of considerable speculation (e.g., [10.29]). The
unsettled nature of capacity assessment is shown in Figure 10.3.1 by the
large variability in capacity assessments done by independent groups
around the world.
To cope with these uncertainties, researchers can return to existing
industries and build on the knowledge and experience base from oil and
gas exploration and production to develop sound concepts for CO 2 stor-
age capacity. In the oil and gas extraction industry, the amount of recov-
erable hydrocarbon is the fundamental measure of the economic value of
a given oil and gas reservoir prior to production. This idea of recoverable
hydrocarbon is analogous to CO 2 storage capacity as discussed further
in this section.