Storage

On various locations in the Netherlands substances are stored in the subsurface facilities. This concerns mainly temporary storage (buffering) of natural gas in gas fields or salt caverns or storage of production water in former oil and gas fields. Salt caverns are also used for storage of nitrogen (Winschoten) and gasoil (Marssteden). Depleted gas fields can form a significant storage option for permanent storage of CO2 in the years to come.

Subsurface storage capacity in the Netherlands

Liquids and gasses may be stored in porous rocks like sandstones ore carbonates in the subsurface or in specifically created cavernes in salt deposits. Solid substances are normally stored in mine shafts. A prerequisite is the injected substance remains within the appointed storage system, so both horizontally and vertically a sealing body of rock is required . Furthermore every type of storage being it natural gas, hydrogen, CO2, formation water, compressed air, gasoil, radio-active waste, etc., has its specific technical and economical criterion. In general these primarily concern 1) the volume of the storage and 2) de rate at which the substance can be injected or withdrawn). For many types of storage the storage depth is of importance as this has implications on the pressure in the storage facility. The following geological elements are potentially important for underground storage in the Netherlands:

  • Gas fields: very suitable as their storage capacity has already been proven by their existence as a gas field. The storage capacity is often large and equals the amount of gas that has been produced from the field. Gas fields in general are potential locations for the buffering of natural gas or the permanent storage of CO2 and formation water.
  • Salt caverns: are suitable for storage as their dimensions may be specifically designed for the storage purpose and because salt is one of the best sealing rocks available in the subsurface. Individual caverns have a relatively small volume but are scalable by using multiple cavern facilities. These caverns have excellent injection and production characteristics and are mainly used for storage of natural gas, industrial gasses, gasoil and compressed air.
  • Aquifers: theoretically can store very large volumes, but in most cases extensive research is necessary to establish the injectivity and the containment (this in contrast to gas fields where exploration and production of the gas has already revealed a comprehensive dataset on the static and dynamic behaviour of the field. Aquifers potentially are great for the storage of thermal energy (high temperature water), CO2, natural gas and formation water. Because the Netherlands has many depleted gas fields, these are the preferred storages over aquifers (this excludes the storage of thermal energy).
     

In Zuid-Limburg thermal energy is stored in a former coal mine. For the final storage of radioactive waste the Netherlands is researching the options in clay and rocksalt.

The estimation of the potential recovery

The re-use of depleted gas fields or salt caverns there is no need for exploration. In specific cases additional measurements on rock properties and production behaviour will have to proof the technical and economic suitability of the cavern and to establish what measures will have to take place to ensure a safe an efficient storage (this may include extra wells to ensure the necessary injection and production rates). Details will be presented in the storage plan which needs approval by the Ministry of Economic Affairs.

Potential interference and re-use options of depleted fields.

Porous reservoirs for storage are often present in layers which are also favourable for geothermal energy. Both activities benefit from high porosity and permeability. For storage the containment by sealing layers is a n extra condition. Although geothermal energy will probably not be exploited within a storage complex, it may very well take place in an adjacent aquifer as long as the two do not affect each other in a negative way. Storage can take place after the gas field is depleted (CO2) or even earlier (natural gas storage). Injection of CO2 or production water may be used to the raise reservoir pressure in order to enhance the oil or gas production.

Storage in salt caverns is hardly interfering with any other activity in the subsurface as the salt is such an excellent sealing layer. When the salt itself is the sealing layer for a storage facility or a producing field, the suitability for caverns may be reduced.

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