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384 12 Carbon Capture and Storage

12.8.3 Saline Aquifer Storage

Saline aquifer storage is a CO 2 storage option for regions without energy resources
recovery opportunities [13, 53]. Similar to EOR, CO 2 is injected into the saline
aquifer as a supercritical fluid, which forms a deeply underground plume. The
storage potential and security risks depend on the geological characteristics and
usually they are predicted by model simulations.
Figure 12.10 shows a schematic diagram of deep saline aquifer CO 2 storage.
CO 2 is injected down to the underground and sealed with a cap rock. Over time,
stored CO 2 migrates slowly out of the CO 2 reservoir as a result of dissolution or
chemical reactions with the cap rock.
There are four primary mechanisms for saline aquifer CO 2 storage, in order of
increasing security
• Structural and stratigraphic trapping
• Residual trapping
• Solubility trapping, and
• Mineral trapping
Structural and stratigraphic trapping CO 2 is trapped under a cap rock. This is
simply an initial and temporary physical trapping of CO 2 for 1–100 years,
depending on the structural characteristics.
Residual trapping As the CO 2 plume rises through a water-saturated rock, high
pressure buoyant CO 2 drives water out of the pores of the rock. Some CO 2 is
trapped in the rock pores as residue. The residual trapping over time declines as
CO 2 is dissolved in the formation brine and diffuses into the surrounding unsatu-
rated aquifer.

Fig. 12.10 Saline aquifer
CO 2 storage