CO2 Sequestration through Deep Saline Injection and ...

the sense that they have lower total dissolved solids (TDS < 10,000 mg/l) as compared to brines
(TDS 10,000 – 100,000 mg/l) [67]. The higher salt concentrations lead to the salting out effect
change in abundance
(volume fraction)
1.00E-04
-2.00E-04
-3.00E-04
-4.00E-04
calcite
0.00E+00
0 2000 4000
-1.00E-04
distance (m)
change in abundance
(volume fraction)
3.00E-06
2.00E-06
1.00E-06
-1.00E-06
siderite
0.00E+00
0 2000 4000
distance (m)
Figure 37
Change in mineral abundance for two of the minerals (negative values indicate dissolution and positive
precipitation) after 50 years. Note that the scales of abundance are different for the four figures
resulting in lesser sequestration capacity of the CO2 in the medium. Thus it is proposed to
determine an area of the aquifer where the salt concentration is relatively lower and inject in that
part of the formation. This possibility will be investigated as injection scenario 2 below.
5.3. AQUIFER INTEGRITY AND LEAKAGE
A crucial aspect of geologic sequestration is the leakage potential of CO2 out of the target
formation. From a global perspective, leakage of CO2 from reservoirs would make CO2
sequestration less effective, or even ineffective as mitigation option (depending on the leakage
rate). The crucial question is what leakage rates are acceptable to assure stabilization of
atmospheric greenhouse concentrations in the coming century is not endangered [68].
Leakage can occur through the seal or the cap rock on top of the storage aquifer, it may also
occur through a faulted zone, especially when the fault covers all the geological layers from the
surface to the basement rock. Furthermore, leakage could occur through abandoned wells.
Abandoned wells may act as a bypass to the atmosphere if these were not sealed properly.
Catastrophic leakage is unlikely for CO2 injected into deep saline aquifers and probably would
occur only as a result of a blowout of an injection well or existing well in the vicinity, or a
seismic disturbance [7], although the tectonically stable nature of the Viking formation [56] does
not favor such an occurrence.
5.3.1. Caprock Integrity
A seal or a caprock is a geological formation capable of hydraulic sealing over geological time
that will maintain it is sealing properties despite of geomechanical, geochemical, and
hydrogeological changes [7]. It is typically a rock of low permeability that serves as a physical
barrier to fluid migration. The permeability of the cap rock is typically in the range of micro-
Darcy (μD) or less, as a result of small grain size and small pore diameters. The tiny pore throats
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