Fluids and Rocks - Introduction to Carbon Capture and Sequestration - page 399

Solubility of CO 2 in groundwater
The solubility of CO 2 in water is another key physical property that has
important consequences for controlling solubility trapping (see Chapter 8).
Figure 9.3.3 shows the solubility profi les for CO 2 in groundwater as a
function of depth or pressure for 0, 2, and 6 molar NaCl brine at two dif-
ferent P - T conditions. The fi gure shows that the solubility of CO 2
increases rapidly with depth, and then declines slightly as both pressure
and temperature increase and CO 2 becomes supercritical.

0

Pure water (0 m NaCl) Gas

Liquid

1000 100

Brine (2 m NaCl)

2000

200

Supercritical

Hypersaline brine
(6 m NaCl)

3000

300

30ºC/km
15ºC/km

4000

0 0.005 0.01 0.015 0.02 0.025 0 50 100

T (ºC)

x li CO 2

Figure 9.3.3 Solubility of CO 2 in fresh and saline water as a function of depth
Solubility of CO 2 in fresh and saline water as a function of depth or pressure at varying
P - T conditions (left) and temperature profi les that highlight the various phases that CO 2
assumes (right). The red dashed lines are for a temperature profi le of 30

° C/km and the

blue solid lines for a profi le of 15 ° C/km. Figure adapted from Oldenburg [9.11] .