In 2000, Hovedstadsområdets Geotermiske Samarbejde (HGS – the Greater Copenhagen Geothermal Cooperation) completed a new seismic survey on- as well as offshore. Based on this it was decided to construct a geothermal demonstration plant at Amagerværket (the Amager combined heat and power plant). In 2003 and 2004, two 2.6 km deep geothermal wells were drilled to the Bunter Sandstone Formation. Tests showed that the thickness, permeability and temperature of the reservoir are good, and following the construction of the surface installations, the plant was commissioned in 2005.
Geothermal energy is an environmentally good supplement to the more traditional methods of producing district heating in larger urban areas. The three large district heating companies in the Greater Copenhagen area – VEKS, CTR and HOFOR – are therefore all part of the Greater Copenhagen Geothermal Cooperation (HGS is the Danish abbreviation) with the purpose of working to advance the production of geothermal energy in the Greater Copenhagen area. Until November 2014, DONG Energy was also a part of HGS.
HGS has in 2001 received a license to explore for and produce geothermal energy in the Greater Copenhagen area.
The plant produces geothermal energy from a reservoir in the Buter Sandstone Formatikon in a depth of 2.6 km. Here the temperature is 73 °C, and an electrical submersible pump (ESP) with a power of 700 kW pumps up to 230 m3 per hour from the reservoir. The water is cooled in heat exchangers to approximately 17 °C before being pumped back into the reservoir through a 400 kW injection pump.
The three absorption heat pumps of the plant are powered by steam from the steambased district heating system, which is still active in some parts of Copenhagen. As a backup, the steam can also be delivered from unit 3 of the Amager CHP plant.
The geothermal plant is split on two nearby locations. The geothermal loop including the wells, pumps, filtering systems, heat exchanger, etc. is located at the farthest end of the power plant peninsula, approximately 25 meters from the shoreline. The absorption heat pumps and the connection to the steam and district heating systems is located next to unit 3 of the Amager CHP plant.
|The geothermal plant on Amager in Copenhagen.|
In total the plant can produce up to 27 MW of district heating, split in 14 MW from the geothermal reservoir and 13 MW from the steam used to power the absorption heat pumps. The plan can yearly produce up to 300,000 GJ, equivalent to the annual heat consumption of approximately 4,600 households or roughly 1 % of the total district heating production in the combined area of supply of CTR, VEKS and HOFOR (excluding HOFOR’s steam system).
As part of the 2-year long programmes set out by the Danish Energy Agency as part of the HGS license, the HGS partners have in 2008 worked out an estimation of the reserves in the entire license area.
The overall conclusions from the estimation are
- There are reserves everywhere in the license area.
- The three main reservoirs – Lower Cretaceos/Lower Jura, Gassum and Bunter Sandstone – all substantially contribute to the reserves.
- The reserves are estimated at more than 60,000 PJ in total. If this figure is compared to the longterm estimate of the district heating production in the license area of 30-40 PJ per year, it can be concluded that with realistic coverages of 30-50 %, there are reserves in the area for thousands of years.
|The HGS license area.|
Reserves should here be understood as the amounts of heat, that can be produced at a competitive price at the time of production. An upper limit of 100 kr./GJ has been chosen, which is on level with the present average price (in 2008 the average price was a bit lower). For calcution purposes a supply of 1/3 of the district heating demand is assumed for those areas that are supplied with geothermal district heating.
The estimate of the reserves is the result of an assessment of the possibilities of the future, solely based on the characteristics of the reservoirs and the technical and economical conditions of the geothermal plant. The possibilities of fitting the geothermal reserves into the existing infrastructure and supply from the existing production units are not taken into account. Production of the local reserves must be established in cooperation with other district heating producers and district heating companies as well as through the heat planning of the local municipalities with due respect for the existing supply conditions and future changes.
The estimation of the reserves in the license area has identified three reservoirs: Lower Cretaceous/Lower Jura, Gassum and Bunter Sandstone, all of them suited for geothermal production. The license area has been split up into 462 blocks, each of them 4 km2, and for each block the reserves are estimated. Due to a relatively limited data coverage as compared to the number of blocks, data for the individual blocks cannot be used on their own; but when seen in connection with the other blocks, they can be used to describe trends within the license area and for an estimation of the total reserves.
For the purpose of estimating the reserves, calculations are done for at geothermal plant with 11 well in a star configuration, that gives a good exploitation of the heat in the reservoirs based on 4 block with a total area of 16 km2. Production over many years will lead to a decline in production temperatures as the heat is produced. If the production over time is compared to the original temperature and heat in place of the reservoir, a correlation is obtained that can afterwards be used on the individual blocks, in order to calculate when the production of a given plant will reach the upper limit of 100 kr./GJ set for the production price.
Furthermore, the reheating of the reservoirs after production in an area has come to a halt has been investigated. The result is that over a long period of time a substantial reheating takes place, which makes reestablishment of production at a later stage in time possible. The reheating is not included in the estimation of the reserves, which can there for be seen as a conservative estimate.
In connection to the World Geothermal Congress 2010 we have written a paper, which can be found here.