Large-Scale Geological Carbon Sequestration - Introduction to Carbon Capture and Sequestration - page 480

sequestration sites that is recognized widely today. Some industries are
building considerable expertise and knowledge about how to carry out
sequestration effectively on the assumption that someday economic
incentives and/or legal imperatives will be in place. Regardless, regula-
tions on injection, monitoring, and verifi cation of storage, legal aspects of
ownership and liability related to the injected CO 2 , and land access com-
prise some of the other non-technical factors that control reserve capac-
ity. As for the technical aspects, most of the issues discussed in the
earlier sections of this chapter relate to aspects of sequestration pro-
cesses that reduce the total resource storage capacity by a large amount
to create the reserve capacity. Here we focus on these process-oriented
or technical aspects of CO 2 storage capacity.
Storage capacity
The injection of CO 2 into a brine-fi lled porous reservoir is a complex pro-
cess that cannot be tightly controlled or engineered once the CO 2 leaves
the wellbore. Instead, the vagaries of the natural system largely control
how the CO 2 fl uid invades and occupies the pore space. An understand-
ing of the processes involved has been developed through theory, expe-
rience with analogous systems, and simulation, but controlling these
processes remains elusive. Figure 10.3.2 illustrates the different factors
that control the fi lling of the pore space by injected CO 2 . Specifi cally,
Figure 10.3.2 (a) illustrates multiphase fl ow effects which, as discussed
in the last chapter, tend to place CO 2 (the non-wetting phase) in the cent-
ers of pores while native groundwater wets the solid grains of the matrix.
Figure 10.3.2 (b) illustrates gravity effects which provide a strong upward
driving force that causes CO 2 to accumulate in the upper regions of the
storage formation because of the density contrast between supercritical
CO 2 and brine. Shown in Figure 10.3.2 (c) are the effects resulting from
heterogeneity in porosity and permeability, which also strongly control
where the CO 2 invades and how it is ultimately trapped. Finally, Figure
10.3.2 (d) shows structural effects, specifi cally the role of dipping strata
in rocks that will encourage long lateral migrations. Doughty et al . [10.30]
defi ned an overall capacity factor C as the product of the porosity and
four capacity factors that represent each of these main effects. The idea
here is that porosity alone does not provide a realistic estimate of capac-
ity in a porous natural rock. Instead, capacity is potentially reduced by