Underground storage

The volume for large liquid or gas storage is most economically provided by suitable bedrock structures. Two principal types of underground storage facilities are to be discerned: rock formations featuring an inherent high porosity (porosity storage reservoir) or solution-mined caverns in thick salt formations, especially salt domes (cavern storage). The sealing of salt caverns is proven by the salt's physical properties and the cap rock. High porosity rock formations (e.g. limestone or sandstone), however, are suitable for underground storage only when covered by an impermeable barrier rock in structural traps. Depleted oil and gas reservoirs are the most commonly used underground storage sites because conversion from production to storage duty can take advantage of existing wells and gathering systems.

Until recently, underground storage most notably focused on safeguarding the availability of gas by balancing the seasonal swings in demand and mitigating import disruptions. Overall 13 gas storage plants are in operation in depleted oil and gas deposits in the German and Austrian parts of the Molasse basin, covering an important amount of the total installed working gas volume of Germany and Austria. Further sites are under development. The Italian Po Basin hosts 9 gas storage sites in exploited hydrocarbon deposits.

Nowadays the enhanced utilization of underground storage potentials is also part of different scenarios for the reduction of greenhouse gas emissions: Renewable energy can be upgraded by storing solar- and wind-derived fuels underground, thus minimizing issues of wind and solar intermittency. Without large-scale geological energy storage of hydrogen, methane or compressed air (CAES), this green energy cannot serve as source of baseload electricity and distributed generation technologies cannot be efficiently integrated. Furthermore, the geological storage of sequestered CO2 (CCS) in suitable subsurface structures can substantially contribute to the reduction of greenhouse gas. However, enhanced exploiting of the Foreland Basins’ storage capacity will put further pressure on the subsurface and may constrain the utilisation of ‘classical’ subsurface resources such as groundwater or oil and gas deposits.

The 3-dimensional models prepared within the scope of GeoMol feature information on the extension and thickness of potential reservoir rocks and adjacent barrier rocks and on crucial structural situations such as structural traps GeoMol, thus, provides an important basis of decision-making for future energy security.

GeoMol is funded by the Alpine Space Programme
as a part of the European Territorial Cooperation 2007-2013
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