The Gassum Formation aquifer and the Skagerrak Formation
The aquifer was developed as river dominated system in the latest Triassic time, mainly as a well drained braided river system. The sandstones are believed to be of good quality. The type wells for these sandstones are in the Danish sector, and the Norwegian part is not explored in the same detail. Outside the mapped area indicated in the figure, the latest Triassic fluvial systems are more clay rich and are developed as discontinuous river sands. In the area indicated, the formation is sealed by the Fjerritslev Formation.
In the Skagerrak area, the Gassum Formation outcrops to the sea floor, and is covered by a Quaternary section which is typically less than 100 m thick. The sealing risks include faults, fracturing above salt structures and long distance migration towards the sea floor. The red areas in the map shows where the burial depth is less than 600 m. Migration of CO2 into these areas should be avoided. The Gassum Formation can be a candidate for CO2 injection in the Skagerrak area, but more data is required to investigate its potential.
The underlying Skagerrak formation is developed as a braidplain in an arid desert environment and as alluvium bor-dering the emergent land area east of the Danish-Norwegian Basin. Scarce well data indicate that the thick sandy sequences of the formation have low permeability, but locally they could interact with the overlying Gassum aquifer. The Skagerrak Formation in the Norwegian sector is poorly known, and with more data it is possible that a storage potential could be defined. In the figure, the outlined area indicates where the Skagerrak Formation is buried to less than 2000 m.
