What impact does CO2 have on groundwater and rock matrix?
The sweet groundwater used for drinking water is not affected at all, because the CO2 will be injected into far deeper, saline water bearing rock layers. These saline aquifers are separated from the sweet water aquifers higher up by several massive impermeable rock layers that keep both the saline waters and the CO2 separate from the surface near groundwater. Pure CO2 is lighter than water and moves upward, displacing the brine towards the bottom. Slowly CO2 dissolves in the brine, lowering its pH value. Ideally, it reacts with Calcium iones and precipitates as Calcite. On the other hand, the carbonic acid is corrosive and might affect well cements, especially if they are old and badly completed. Such wells must be worked over prior to storage operation. There are numerous research projects ongoing about the interactions between CO2, the formation waters, and the rock matrix. The results are used in the practical tests of the CCS technology.
