Geothermal energy has been seen for quite some time as a potentially sustainable source of energy, but it was not until 2007 that it was first successfully taken into production in the Netherlands. This form of energy has really taken off since then, and many new licences have been applied for and new projects initiated.
Areas suitable for recovering geothermal energy in the Netherlands
Until now, all geothermal energy recovered in the Netherlands has been from highly permeable and porous aquifers with temperatures ranging from 40oC to around 100oC. The recovery technique involves well pairs (in Dutch: doublets): two wells drilled into the same aquifer, thus enabling hot groundwater to be pumped up through one well, while the cooled-down water is injected back into the same aquifer through the other well. Suitable aquifers are present in large parts of the Netherlands and were identified during hydrocarbon exploration.
A study is currently ongoing into the technical feasibility and economic viability of producing geothermal energy from much deeper aquifers at much higher temperatures. In these cases, fluid flow will generally have to be enhanced by applying techniques such as fracking. Although the high temperatures envisaged can be accessed anywhere by drilling sufficiently deep wells, it is not yet known whether the rocks at these depths are suitable for production as the target depth is much greater than the interval explored during conventional oil and gas operations. As a result, these rock strata have rarely been penetrated by the drill bit.
Determining potential recoverability
Just like in the search for oil and gas, an exploration well is drilled first to test the geothermal energy potential of an aquifer. This will indicate whether an aquifer is suitable, particularly with respect to flow properties and temperature. If the exploration well is successful, a second well can be drilled to complete the well pair. Before production can start, a production plan has to be submitted and approved by the Minister.
Possible interference and re-use of depleted fields
Geothermal energy can often be produced from aquifers that may also host conventional oil and gas fields. Depleted oil and gas accumulations are often found in strata that are also prospective for geothermal energy production and/or storage facilities. Many of these applications benefit from good porosity and permeability. In the event of oil and gas accumulations and storage facilities, the effectiveness of the reservoir seal is also important. Geothermal energy projects will generally not be planned in an undepleted oil or gas field, but may be implemented in an adjoining aquifer if the two activities do not interfere with each other. Suitable candidates for storage facilities (e.g. for CO2 storage) are depleted gas fields – when production has ceased – or even producing gas fields (for use as a gas storage facility). During or after oil or gas production, formation water can be pumped back into the deeper part of the aquifer.
Maps, data and information
Details of prospective areas for geothermal energy production can be found here:
- Information sheet geothermal energy (in Dutch)
- Outline map of the geothermal energy potential of the Netherlands
- Geothermal energy potential of Rotliegend aquifers
- Geothermal energy potential of Triassic aquifers
- Geothermal energy potential of Jurassic/Cretaceous aquifers
- Geothermal energy potential of Tertiary aquifer
- Possibly prospective areas for geothermal energy production at >120oC