The Danish subsoil is used for more than just the production of
oil and gas. The subsoil is used to extract salt and geothermal
heat and to store natural gas, and also the potential future use
for storage of CO2.
With the exception of salt extraction, it is largely the same
types of layers in the subsoil which can be used for these various
purposes. It is necessary to prioritize use of the subsoil for
different purposes, as the storage of CO2 will for
example permanently prevent the layers from being used for other
purposes.
In connection with geothermal heat production, the storage of
natural gas and CO2, subsoil porous and permeable
sandstone layers at depths of 1,500 m to 2,500 m can be used in
many areas in Denmark. The capture and storage of CO2
and gas storage require the porous sandstone layers used for
capture/storage to be part of a geological structure that permits
the gases injected to be trapped in the porous layers. Above the
porous layers, there must be a seal or cap consisting of tight clay
layers which are impermeable to the injected gases. On the other
hand, the use of porous sandstone layers for geothermal heat
production does not require a subsoil structure. Porous sandstone
layers which contain hot water are sufficient to enable the
production of geothermal heat.