geothermal energy in denmark â€“ an environmentally compatible

IOP Conference Series Earth and Environmental Science

OPEN ACCESS

Geothermal energy in Denmark ndash anenvironmentally compatible supplement to the totalenergy supplyTo cite this article Anders Mathiesen et al 2009 IOP Conf Ser Earth Environ Sci 6 192029

View the article online for updates and enhancements

You may also likeMotivation to adapt to climate changeKristina Blennow

-

Forest management for increased carbonstorageJens Peter Skovsgaard and L Vesterdal

-

The potential role of atmospheric nutrientsupply in altering ocean productivityTimothy Jickells and A L Baker

-

This content was downloaded from IP address 2221124946 on 06112021 at 0751

P1921 Geothermal energy in Denmark - an environmentally compatible supplement to the total energy supply Anders Mathiesen LH Nielsen T Bidstrup Geological Survey of Denmark and Greenland Department of Geophysics Copenhagen Denmark Concerns with respect to CO2 emission to the global atmosphere and climate changes have led to increased interest in the utilisation of geothermal energy as one possible way of reducing the consumption of fossil fuels Utilisation of geothermal energy is a well-established technology with more than one hundred plants currently operating in Europe maintaining a large degree of security of supply and with no visual and noise inconveniences Existing Danish geothermal plants can produce large amounts of heat using only a minimum power to extract the heat from the subsurface water pumped to the surface and afterward circulated in a closed system back to the subsurface In general a 15 MW geothermal plant based on reservoir properties as in the Gassum Formation can deliver the same effect as ~30 windmills The Danish subsurface consists of two geological basins (the Danish Basin and the North German Basin) several kilometres tick and separated by a structural high (the Ringkoslashbing-Fyn High Fig 1) Regional geological studies have shown that both basins have large areas with geothermal potential as they contain several sandstone-rich formations and water bearing intervals 1000ndash2500 m below the surface with formation temperatures between 25ndash70ordmC (Nielsen et al 2004) The four major structural features ndash the Danish Basin the Sorgenfrei-Tornquist Zone the Ringkoslashbing-Fyn High and the North German Basin ndash exert the overall control on the geothermal prospectivity of Denmark (Nielsen 2003) They essentially determine the distribution thickness facies types and burial depths of the stratigraphic units with potential reservoirs (Fig 1) Due to uplift of most of the basins and the Ringkoslashbing-Fyn High in early Middle Jurassic time the TriassicndashLower Jurassic succession is truncated by the lsquoBase Middle Jurassic Unconformityrsquo which shows a progressively deeper truncation towards the Ringkoslashbing-Fyn High (Fig 2) The Sorgenfrei-Tornquist Zone crosses northern Jutland Kattegat the northern part of Oslashresund and southern Sweden It is a strongly block-faulted zone with tilted Palaeozoic fault blocks overlain by thick Mesozoic deposits This zone experienced continuous but slow subsidence during the Middle Jurassic regional uplift that affected the Danish Basin and the Ringkoslashbing-Fyn High and thick paralic sandstones were deposited in the zone these sandstones form excellent reservoirs (Haldager Sand Formation Fig 2) The most promising reservoirs occur within the TriassicndashLower Cretaceous succession (Fig 2) This succession has been the target of hydrocarbon exploration since 1935 and is thus known from about 60 deep wells and seismic data acquired over many years although with a very variable data quality and coverage Based on regional geological studies four main stratigraphic units with a regional geothermal potential have been identified (Fig 2) Combining the distribution of the these stratigraphic units with an estimate of where sand thickness of the formations exceeds 25 m at depths of 1000ndash2500 m provides a useful indication of regional geothermal potential Figure 1 displays the potential for the land area of Denmark in a general manner and indicates which sandstone-rich formations need further more detailed research and investigation for geothermal energy production Temperature and salinity of the formation water in these potential reservoirs increase with increasing depth The temperature-depth relation is well established and is rather uniformly developed over the Danish area with a general gradient of about 25ndash30degC per km The salinity shows a general increase of about 10 per km burial depth but great variations are found Porosity and permeability decrease with increasing depth due to mechanical compaction and the formation of diagenetic minerals that reduce pore volume and pore connections Permeability is very critical but difficult to predict since very large variations are found depending on depositional facies provenance mineralogical composition burial history and position in the basin Several of these factors are directly related to the depositional processes during the formation of the reservoirs but their mutual dependency are not fully understood which weakens the predictive strength of the current geological models used for identifying areas of interest Thus one of the main technical barriers for increasing the exploitation of the geothermal resource is the geological uncertainty that is related to the presence of a sufficiently high-quality reservoir in the subsurface below the major cities with the infrastructures and consumers in place During the last 5ndash10 years use of geothermal energy has experienced an increasing interest So far the Thisted plant in northern Jutland and the Margretheholm demonstration-plant near Copenhagen are the only two working geothermal plants in Denmark (Fig 1) The Thisted plant has produced heat from the Gassum Formation for almost 20 years without notable production or injection problems In connection with the Margretheholm demonstration-

Climate Change Global Risks Challenges and Decisions IOP PublishingIOP Conf Series Earth and Environmental Science 6 (2009) 192029 doi1010881755-130769192029

ccopy 2009 IOP Publishing Ltd 1

plant new seismic data were acquired in 2001 and the Survey carried out geological evaluation of the geothermal potential in the greater Copenhagen area based on well and seismic data from Denmark Oslashresund and southern Sweden Two new Margretheholm-1 and -2 wells were drilled to about 2700 m in 2002ndash2003 and confirmed the presence of several possible sandstone aquifers including the Gassum and Bunter Sandstone Formations (Fig 2) The wells encountered a promising aquifer in the Bunter Sandstone with promising test results and a geothermal power plant was opened in 2006 based on the utilisation of c 70degC geothermal water To increase the geothermal exploitation it is important to enhance the geological understanding of the geothermal reservoirs in the Danish subsurface and to reduce the risks in geothermal prospecting It is estimated that the geothermal resource in Denmark amounts to several hundred years of the present heat consumption and only a small fraction of this potential is utilised by the geothermal power plants in Thisted and Copenhagen A more environmentally compatible Denmark has to include use of geothermal energy at least as a supplement to total energy supply Thus it is important that our geological understanding of the Danish subsurface are currently improved and methods further developed so that the geologic risks are minimized This can only be done by new data and continuous research


2

Figure 1


3

Figure 2 References Nielsen LH 2003 Late Triassic ndash Jurassic development of the Danish Basin and the Fennoscandian Border Zone southern Scandinavia In Ineson JR amp Surlyk F (eds) The Jurassic of Denmark and Greenland Geological Survey of Denmark and Greenland Bulletin 1 459ndash526 Nielsen LH Mathiesen A amp Bidstrup T 2004 Geothermal energy in Denmark Review of Survey activities 2003 Geological Survey of Denmark and Greenland bulletin 4 p17ndash20 Fig 1 Map of Denmark showing the regional geothermal potential of possible aquifer formations based on a burial depth of 1000ndash2500 m and a sand thickness of more than 25 m White areas in Denmark indicate that the reservoir is not present (Ringkoslashbing-Fyn High) too shallow (northernmost Jutland) or too deeply buried (central part of Danish Basin) The locations of the Thisted geothermal plant and the new geothermal site at Margretheholm in Copenhagen are shown Fig 2 Generalised stratigraphic scheme of the Danish onshore area along a NWndashSE-trending cross-section The formations with potential aquifers are indicated in yellow and brown Note the pronounced erosion surfaces at the base of the Middle Jurassic and Lower Cretaceous and the progressive onlap to these surfaces These features have a major influence on the regional distribution and burial depths of potential reservoirs AG Stratigraphic position of the Arnager Groslashnsand Formation NGB North German Basin RKF Ringkoslashbing-Fyn High SKP Skagerrak Platform STZ Sorgenfrei-Tornquist Zone


4

P1921 Geothermal energy in Denmark - an environmentally compatible supplement to the total energy supply Anders Mathiesen LH Nielsen T Bidstrup Geological Survey of Denmark and Greenland Department of Geophysics Copenhagen Denmark Concerns with respect to CO2 emission to the global atmosphere and climate changes have led to increased interest in the utilisation of geothermal energy as one possible way of reducing the consumption of fossil fuels Utilisation of geothermal energy is a well-established technology with more than one hundred plants currently operating in Europe maintaining a large degree of security of supply and with no visual and noise inconveniences Existing Danish geothermal plants can produce large amounts of heat using only a minimum power to extract the heat from the subsurface water pumped to the surface and afterward circulated in a closed system back to the subsurface In general a 15 MW geothermal plant based on reservoir properties as in the Gassum Formation can deliver the same effect as ~30 windmills The Danish subsurface consists of two geological basins (the Danish Basin and the North German Basin) several kilometres tick and separated by a structural high (the Ringkoslashbing-Fyn High Fig 1) Regional geological studies have shown that both basins have large areas with geothermal potential as they contain several sandstone-rich formations and water bearing intervals 1000ndash2500 m below the surface with formation temperatures between 25ndash70ordmC (Nielsen et al 2004) The four major structural features ndash the Danish Basin the Sorgenfrei-Tornquist Zone the Ringkoslashbing-Fyn High and the North German Basin ndash exert the overall control on the geothermal prospectivity of Denmark (Nielsen 2003) They essentially determine the distribution thickness facies types and burial depths of the stratigraphic units with potential reservoirs (Fig 1) Due to uplift of most of the basins and the Ringkoslashbing-Fyn High in early Middle Jurassic time the TriassicndashLower Jurassic succession is truncated by the lsquoBase Middle Jurassic Unconformityrsquo which shows a progressively deeper truncation towards the Ringkoslashbing-Fyn High (Fig 2) The Sorgenfrei-Tornquist Zone crosses northern Jutland Kattegat the northern part of Oslashresund and southern Sweden It is a strongly block-faulted zone with tilted Palaeozoic fault blocks overlain by thick Mesozoic deposits This zone experienced continuous but slow subsidence during the Middle Jurassic regional uplift that affected the Danish Basin and the Ringkoslashbing-Fyn High and thick paralic sandstones were deposited in the zone these sandstones form excellent reservoirs (Haldager Sand Formation Fig 2) The most promising reservoirs occur within the TriassicndashLower Cretaceous succession (Fig 2) This succession has been the target of hydrocarbon exploration since 1935 and is thus known from about 60 deep wells and seismic data acquired over many years although with a very variable data quality and coverage Based on regional geological studies four main stratigraphic units with a regional geothermal potential have been identified (Fig 2) Combining the distribution of the these stratigraphic units with an estimate of where sand thickness of the formations exceeds 25 m at depths of 1000ndash2500 m provides a useful indication of regional geothermal potential Figure 1 displays the potential for the land area of Denmark in a general manner and indicates which sandstone-rich formations need further more detailed research and investigation for geothermal energy production Temperature and salinity of the formation water in these potential reservoirs increase with increasing depth The temperature-depth relation is well established and is rather uniformly developed over the Danish area with a general gradient of about 25ndash30degC per km The salinity shows a general increase of about 10 per km burial depth but great variations are found Porosity and permeability decrease with increasing depth due to mechanical compaction and the formation of diagenetic minerals that reduce pore volume and pore connections Permeability is very critical but difficult to predict since very large variations are found depending on depositional facies provenance mineralogical composition burial history and position in the basin Several of these factors are directly related to the depositional processes during the formation of the reservoirs but their mutual dependency are not fully understood which weakens the predictive strength of the current geological models used for identifying areas of interest Thus one of the main technical barriers for increasing the exploitation of the geothermal resource is the geological uncertainty that is related to the presence of a sufficiently high-quality reservoir in the subsurface below the major cities with the infrastructures and consumers in place During the last 5ndash10 years use of geothermal energy has experienced an increasing interest So far the Thisted plant in northern Jutland and the Margretheholm demonstration-plant near Copenhagen are the only two working geothermal plants in Denmark (Fig 1) The Thisted plant has produced heat from the Gassum Formation for almost 20 years without notable production or injection problems In connection with the Margretheholm demonstration-


ccopy 2009 IOP Publishing Ltd 1



2

Figure 1


3



4



2

Figure 1


3



4

Figure 1


3



4



4

geothermal energy in denmark â€“ an environmentally compatible

Documents