Geological Survey of Denmark and Greenland Bulletin
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Nr. 4, Review of Survey activities 2003, pp. 17-20 |
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The Geological Survey of Denmark and Greenland (GEUS)
has for many years been involved with research, advisory and
consultancy services concerning the assessment of the
geothermal energy potential in Denmark, in close coopera-
tion with private and public partners. The Survey's particular
responsibility has been the development of geological models
to describe and predict the distribution of sandstone reser-
voirs suitable for geothermal exploitation. Danish geother-
mal resources in known sandstone aquifers are estimated to
be sufficient to cover household heating requirements in
Denmark for more than a century (Sørensen et al. 1998).
has for many years been involved with research, advisory and
consultancy services concerning the assessment of the
geothermal energy potential in Denmark, in close coopera-
tion with private and public partners. The Survey's particular
responsibility has been the development of geological models
to describe and predict the distribution of sandstone reser-
voirs suitable for geothermal exploitation. Danish geother-
mal resources in known sandstone aquifers are estimated to
be sufficient to cover household heating requirements in
Denmark for more than a century (Sørensen et al. 1998).
Background
Utilisation of geothermal energy is a well-established techno-
logy with more than one hundred plants currently operating
in Europe. Concerns with respect to CO
logy with more than one hundred plants currently operating
in Europe. Concerns with respect to CO
2
emission to the
global atmosphere have led to increased interest in the utili-
sation of geothermal energy as one possible way of reducing
the consumption of fossil fuels.
sation of geothermal energy as one possible way of reducing
the consumption of fossil fuels.
In 1983, Dansk Olie & Naturgas A/S (DONG A/S) was
granted a sole concession for the exploration and production
of geothermal energy in the entire land area in Denmark. In
of geothermal energy in the entire land area in Denmark. In
Fig. 1. Map of Denmark showing the regional
geothermal potential of possible aquifer forma-
tions, based on a burial depth of 10002500 m
and a sand thickness of more than 25 m. White
areas in Denmark indicate that the reservoir is not
present (RingkøbingFyn 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.
Geological Survey of Denmark and Greenland Bulletin 4, 1720 (2004) © GEUS, 2004
Geothermal energy in Denmark
Lars Henrik Nielsen, Anders Mathiesen and Torben Bidstrup
1993 and 2003, selected parts of the concession area were
returned to the State in accordance with the licensing terms.
returned to the State in accordance with the licensing terms.
The first comprehensive study of Danish geothermal
resources was presented by Michelsen et al. (1981), which
incorporates seismic and well data from the Danish onshore
areas, with a focus on sandstone aquifers between 2000 and
3000 m depth. The Survey's contributions to the two vol-
umes of the atlas of geothermal resources published by the
Euro-pean Commission (Haenel & Staroste 1988; Hurter &
Haenel 2002) have presented data and information that
identify areas of interest for further geothermal exploration.
incorporates seismic and well data from the Danish onshore
areas, with a focus on sandstone aquifers between 2000 and
3000 m depth. The Survey's contributions to the two vol-
umes of the atlas of geothermal resources published by the
Euro-pean Commission (Haenel & Staroste 1988; Hurter &
Haenel 2002) have presented data and information that
identify areas of interest for further geothermal exploration.
Initially it was believed that geothermal heat could be pro-
duced from deep, hot aquifers, and in the early 1980s sand-
stones of the Upper Triassic Gassum Formation were tested at
depths of c. 3000 m in three wells in northern Jutland (Fig.
1). Thick sandstones were encountered, but permeability was
stones of the Upper Triassic Gassum Formation were tested at
depths of c. 3000 m in three wells in northern Jutland (Fig.
1). Thick sandstones were encountered, but permeability was
insufficient and the results were discouraging. However, tech-
nological innovation during the past decade has shifted inter-
est from deep and hot, but high-risk reservoirs, towards
shallower aquifers with good porosity and permeability and
thus the potential of producing large volumes of warm water.
Following heat extraction, the cold water is re-injected into
the aquifer at some distance from the producing well via an
injection well, in order to maintain reservoir pressure and
avoid mixing the cold return water with the warm formation
water.
nological innovation during the past decade has shifted inter-
est from deep and hot, but high-risk reservoirs, towards
shallower aquifers with good porosity and permeability and
thus the potential of producing large volumes of warm water.
Following heat extraction, the cold water is re-injected into
the aquifer at some distance from the producing well via an
injection well, in order to maintain reservoir pressure and
avoid mixing the cold return water with the warm formation
water.
Areas of potential interest
Four major structural features the Danish Basin, the
SorgenfreiTornquist Zone, the RingkøbingFyn High and
the North German Basin exert the overall control on the
geothermal prospectivity of Denmark. They essentially deter-
mine the distribution, thickness, facies types and burial
depths of the stratigraphic units with potential reservoirs
(Fig. 1).
SorgenfreiTornquist Zone, the RingkøbingFyn High and
the North German Basin exert the overall control on the
geothermal prospectivity of Denmark. They essentially deter-
mine the distribution, thickness, facies types and burial
depths of the stratigraphic units with potential reservoirs
(Fig. 1).
The Danish Basin is bounded by the RingkøbingFyn
High to the south and the SorgenfreiTornquist Zone to the
north-east. The Upper Permian Cenozoic basin-fill is 56.5
km thick along the basin axis, increasing locally to more than
9 km in the SorgenfreiTornquist Zone. The Triassic Lower
Cretaceous succession has a relatively uniform thickness in
most of the basin with some thinning towards the Ringkø-
bingFyn High. Due to uplift of most of the basin and the
RingkøbingFyn High in early Middle Jurassic time, the
Triassic Lower Jurassic succession is truncated by the `Base
Middle Jurassic Unconformity', which shows a progressively
deeper truncation towards the RingkøbingFyn High (Fig.
2). On the high the Lower Jurassic, and in places parts of the
Triassic, have been eroded. Regional subsidence gradually
took over again in late Middle early Late Jurassic time and
became more widespread, as shown by a progressively
younger Upper Jurassic Lower Cretaceous onlap onto the
unconformity towards the high. These events have great
influence on the distribution of reservoirs and the thickness
of the overburden. Thus, the Lower Triassic reservoirs may be
found at moderate depths on the RingkøbingFyn High and
along the northern and southern (North German Basin)
flanks of the high.
north-east. The Upper Permian Cenozoic basin-fill is 56.5
km thick along the basin axis, increasing locally to more than
9 km in the SorgenfreiTornquist Zone. The Triassic Lower
Cretaceous succession has a relatively uniform thickness in
most of the basin with some thinning towards the Ringkø-
bingFyn High. Due to uplift of most of the basin and the
RingkøbingFyn High in early Middle Jurassic time, the
Triassic Lower Jurassic succession is truncated by the `Base
Middle Jurassic Unconformity', which shows a progressively
deeper truncation towards the RingkøbingFyn High (Fig.
2). On the high the Lower Jurassic, and in places parts of the
Triassic, have been eroded. Regional subsidence gradually
took over again in late Middle early Late Jurassic time and
became more widespread, as shown by a progressively
younger Upper Jurassic Lower Cretaceous onlap onto the
unconformity towards the high. These events have great
influence on the distribution of reservoirs and the thickness
of the overburden. Thus, the Lower Triassic reservoirs may be
found at moderate depths on the RingkøbingFyn High and
along the northern and southern (North German Basin)
flanks of the high.
The SorgenfreiTornquist Zone crosses northern Jutland,
Kattegat, the northern part of Øresund and southern
Sweden. It is a strongly block-faulted zone with tilted Palae-
ozoic fault blocks overlain by thick Mesozoic deposits (Fig.
1). This zone experienced continuous, but slow, subsidence
during the Middle Jurassic regional uplift that affected the
Danish Basin and the RingkøbingFyn High, and thick par-
alic sandstones were deposited in the zone; these sandstones
Sweden. It is a strongly block-faulted zone with tilted Palae-
ozoic fault blocks overlain by thick Mesozoic deposits (Fig.
1). This zone experienced continuous, but slow, subsidence
during the Middle Jurassic regional uplift that affected the
Danish Basin and the RingkøbingFyn High, and thick par-
alic sandstones were deposited in the zone; these sandstones
18
Fig. 2. Generalised stratigraphic scheme of the Danish onshore area
along a NWSE-trending cross-section. The formations with potential
aquifers are indicated in yellow and brown. Note the pronounced ero-
sion 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 Grønsand For-
mation; NGB, North German Basin; RKF, RingkøbingFyn High; SKP,
Skagerrak Platform; STZ, SorgenfreiTornquist Zone.
form excellent reservoirs (Haldager Sand Formation; Fig. 2).
The zone is further characterised by pronounced late
Cretaceous early Tertiary tectonic inversion with the uplift
of potential reservoirs.
The zone is further characterised by pronounced late
Cretaceous early Tertiary tectonic inversion with the uplift
of potential reservoirs.
Potential reservoirs
The most promising reservoirs occur within the Triassic
Lower 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
(e.g. Bertelsen 1978, 1980; Michelsen et al. 2003; Nielsen
2003) a number of stratigraphic units with a regional geo-
thermal potential have been identified. These include the
LowerUpper Triassic Bunter Sandstone and Skagerrak For-
mations, the Upper Triassic Lower Jurassic Gassum For-
mation, the Middle Jurassic Haldager Sand Formation and
the Upper Jurassic Lower Cretaceous Frederikshavn For-
mation. Other formations may locally contain potential
aquifers, such as the fine-grained sandstones of the F-II
Member of the Fjerritslev Formation on the Skagerrak
Kattegat Platform, and the Arnager Grønsand Formation in
easternmost Zealand.
Lower 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
(e.g. Bertelsen 1978, 1980; Michelsen et al. 2003; Nielsen
2003) a number of stratigraphic units with a regional geo-
thermal potential have been identified. These include the
LowerUpper Triassic Bunter Sandstone and Skagerrak For-
mations, the Upper Triassic Lower Jurassic Gassum For-
mation, the Middle Jurassic Haldager Sand Formation and
the Upper Jurassic Lower Cretaceous Frederikshavn For-
mation. Other formations may locally contain potential
aquifers, such as the fine-grained sandstones of the F-II
Member of the Fjerritslev Formation on the Skagerrak
Kattegat Platform, and the Arnager Grønsand Formation in
easternmost Zealand.
The Bunter Sandstone Formation is present south of the
RingkøbingFyn High, on parts of the high and in the
Danish Basin. It grades into the Skagerrak Formation
towards the north-eastern basin margin (Bertelsen 1978,
1980). The Bunter Sandstone Formation is dominated by
fine-grained sandstones, mainly deposited in an arid conti-
nental environment dominated by fluvial channels, aeolian
dunes and marginal marine facies. The Skagerrak Formation
is less well known, but its marginal distribution along the
northern and north-eastern basin margin, and the coarse-
grained, often poorly sorted sandstones interbedded with
claystones, suggest deposition in alluvial fans and lakes.
Danish Basin. It grades into the Skagerrak Formation
towards the north-eastern basin margin (Bertelsen 1978,
1980). The Bunter Sandstone Formation is dominated by
fine-grained sandstones, mainly deposited in an arid conti-
nental environment dominated by fluvial channels, aeolian
dunes and marginal marine facies. The Skagerrak Formation
is less well known, but its marginal distribution along the
northern and north-eastern basin margin, and the coarse-
grained, often poorly sorted sandstones interbedded with
claystones, suggest deposition in alluvial fans and lakes.
The Gassum Formation is present in almost the entire
Danish area, and shows a remarkable lateral continuity with
thickness generally between 100 and 150 m with a maximum
of about 300 m in the SorgenfreiTornquist Zone (Michelsen
et al. 2003; Nielsen 2003). The formation consists of fine- to
medium-grained, locally coarse-grained, sandstones inter-
bedded with heteroliths, claystones and thin coals. The late-
rally continuous shoreface sandstones were deposited by
repeated shoreline progradation. Fluvial and estuarine sand-
stones dominate the lowermiddle part of the formation in
the SorgenfreiTornquist Zone.
thickness generally between 100 and 150 m with a maximum
of about 300 m in the SorgenfreiTornquist Zone (Michelsen
et al. 2003; Nielsen 2003). The formation consists of fine- to
medium-grained, locally coarse-grained, sandstones inter-
bedded with heteroliths, claystones and thin coals. The late-
rally continuous shoreface sandstones were deposited by
repeated shoreline progradation. Fluvial and estuarine sand-
stones dominate the lowermiddle part of the formation in
the SorgenfreiTornquist Zone.
The Haldager Sand Formation is up to 200 m thick in the
SorgenfreiTornquist Zone, and shows a marked thinning
towards the south-west and north-east (Michelsen et al.
towards the south-west and north-east (Michelsen et al.
2003; Nielsen 2003). It consists of thick, fine- to coarse-
grained sandstones alternating with thin siltstones, claystones
and coals, deposited in shallow marine, estuarine, fluvial and
lacustrine environments.
grained sandstones alternating with thin siltstones, claystones
and coals, deposited in shallow marine, estuarine, fluvial and
lacustrine environments.
The Frederikshavn Formation is present in the northern
part of the Danish area, and shows marked thickness varia-
tions (75235 m), reaching a maximum in the Sorgen-
freiTornquist Zone (Michelsen et al. 2003). The formation
consists of siltstones and fine-grained sandstones interbedded
with claystones.
tions (75235 m), reaching a maximum in the Sorgen-
freiTornquist Zone (Michelsen et al. 2003). The formation
consists of siltstones and fine-grained sandstones interbedded
with claystones.
Temperature and salinity of the formation water in these
potential reservoirs increase with increasing depth. The tem-
peraturedepth relation is well established, and is rather uni-
formly developed over the Danish area with a general
gradient of about 30°C per km. The salinity shows a general
increase of about 10% per km burial depth, but great varia-
tions are found. Porosity and permeability decrease with
increasing depth due to mechanical compaction and the for-
mation 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. These relationships
and their mutual dependency are not fully understood,
which weakens the predictive strength of the current geolog-
ical models used for identifying areas of interest. However,
combining the distribution of the above-described forma-
tions with an estimate of where sand thickness of the forma-
tions exceeds 25 m at depths of 10002500 m provides a
useful indication of regional geothermal potential. Figure 1
displays the potential for the land area of Denmark in a gen-
eral manner, and indicates which formations may warrant
further investigation for geothermal energy production.
peraturedepth relation is well established, and is rather uni-
formly developed over the Danish area with a general
gradient of about 30°C per km. The salinity shows a general
increase of about 10% per km burial depth, but great varia-
tions are found. Porosity and permeability decrease with
increasing depth due to mechanical compaction and the for-
mation 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. These relationships
and their mutual dependency are not fully understood,
which weakens the predictive strength of the current geolog-
ical models used for identifying areas of interest. However,
combining the distribution of the above-described forma-
tions with an estimate of where sand thickness of the forma-
tions exceeds 25 m at depths of 10002500 m provides a
useful indication of regional geothermal potential. Figure 1
displays the potential for the land area of Denmark in a gen-
eral manner, and indicates which formations may warrant
further investigation for geothermal energy production.
Existing and planned geothermal facilities
The Thisted plant in northern Jutland is the only working
geothermal plant in Denmark, although a second plant is
currently under construction in Copenhagen (Fig. 1). The
Thisted plant has produced heat from the Gassum Formation
for almost 20 years without notable production or injection
problems.
geothermal plant in Denmark, although a second plant is
currently under construction in Copenhagen (Fig. 1). The
Thisted plant has produced heat from the Gassum Formation
for almost 20 years without notable production or injection
problems.
A study of the geothermal potential in the Copen-
hagenMalmö region was initiated in the year 2000 on
behalf of DONG A/S encouraged by financial support from
the Danish Government and technological developments
that make the utilisation of relatively low temperature for-
mation water possible. The subsurface of the greater Copen-
hagen area was previously poorly known, as no deep wells
existed and seismic data coverage was very poor. New seismic
data were acquired in 2001, and the Survey has carried out a
behalf of DONG A/S encouraged by financial support from
the Danish Government and technological developments
that make the utilisation of relatively low temperature for-
mation water possible. The subsurface of the greater Copen-
hagen area was previously poorly known, as no deep wells
existed and seismic data coverage was very poor. New seismic
data were acquired in 2001, and the Survey has carried out a
19
20
geological evaluation of the geothermal potential at seven
localities in the greater Copenhagen area, based on integra-
tion of the new data with existing well and seismic data from
Denmark, Øresund and southern Sweden. The evaluation
indicated the presence of several possible sandstone aquifers,
including the Gassum and Bunter Sandstone Formations.
The Margretheholm location close to the centre of Copen-
hagen was selected for further investigations, and a vertical
well was drilled to about 2700 m in 2002 (Fig. 3). The well
encountered a promising aquifer in the Bunter Sandstone
Formation, and a second, deviated well was drilled to the
same aquifer in 2003. The test results were promising, and a
geothermal power plant is now under construction based on
localities in the greater Copenhagen area, based on integra-
tion of the new data with existing well and seismic data from
Denmark, Øresund and southern Sweden. The evaluation
indicated the presence of several possible sandstone aquifers,
including the Gassum and Bunter Sandstone Formations.
The Margretheholm location close to the centre of Copen-
hagen was selected for further investigations, and a vertical
well was drilled to about 2700 m in 2002 (Fig. 3). The well
encountered a promising aquifer in the Bunter Sandstone
Formation, and a second, deviated well was drilled to the
same aquifer in 2003. The test results were promising, and a
geothermal power plant is now under construction based on
the utilisation of c. 70°C geothermal water. When estab-
lished, the plant is expected to produce around 400 TJ heat
annually, corresponding to 1% of the total heating demand
of the Copenhagen area, with an option for future expansion.
lished, the plant is expected to produce around 400 TJ heat
annually, corresponding to 1% of the total heating demand
of the Copenhagen area, with an option for future expansion.
As a direct result of the successful efforts in Copenhagen,
geothermal exploration has now been resumed in other parts
of the onshore Danish area. GEUS is currently cooperating
with DONG A/S on the identification and assessment of sev-
eral prospective sites.
of the onshore Danish area. GEUS is currently cooperating
with DONG A/S on the identification and assessment of sev-
eral prospective sites.
References
Bertelsen, F. 1978: The Upper Triassic Lower Jurassic Vinding and
Gassum Formations of the NorwegianDanish Basin. Danmarks
Geologiske Undersøgelse Serie B 3, 26 pp.
Geologiske Undersøgelse Serie B 3, 26 pp.
Bertelsen, F. 1980: Lithostratigraphy and depositional history of the
Danish Triassic. Danmarks Geologiske Undersøgelse Serie B 4, 59 pp.
Haenel, R. & Staroste, E. (eds) 1988: Atlas of geothermal resources in the
European Community, Austria and Switzerland. Commission of the
European Communities, Publication EUR 11026, 74 pp., 110 plates.
European Communities, Publication EUR 11026, 74 pp., 110 plates.
Hurter, S. & Haenel, R. (eds) 2002: Atlas of geothermal resources in
Europe. European Commission, Publication EUR 17811, 92 pp., 89
plates.
plates.
Michelsen, O. et al. 1981: Kortlægning af potentielle geotermiske reser-
voirer i Danmark. Danmarks Geologiske Undersøgelse Serie B 5, 28
pp.
pp.
Michelsen, O., Nielsen, L.H., Johannessen, P.N., Andsbjerg, J. & Surlyk,
F. 2003: Jurassic lithostratigraphy and stratigraphic development
onshore and offshore Denmark. In: Ineson, J.R & Surlyk, F. (eds): The
Jurassic of Denmark and Greenland. Geological Survey of Denmark
and Greenland Bulletin 1, 147216.
onshore and offshore Denmark. In: Ineson, J.R & Surlyk, F. (eds): The
Jurassic of Denmark and Greenland. Geological Survey of Denmark
and Greenland Bulletin 1, 147216.
Nielsen, L.H. 2003: Late Triassic Jurassic development of the Danish
Basin and the Fennoscandian Border Zone, southern Scandinavia. In:
Ineson, J.R & Surlyk, F. (eds): The Jurassic of Denmark and Greenland.
Geological Survey of Denmark and Greenland Bulletin 1, 459526.
Ineson, J.R & Surlyk, F. (eds): The Jurassic of Denmark and Greenland.
Geological Survey of Denmark and Greenland Bulletin 1, 459526.
Sørensen, K., Nielsen, L.H., Mathiesen, A. & Springer, N. 1998: Geotermi
i Danmark: Geologi og ressourcer. Danmarks og Grønlands
Geologiske Undersøgelse Rapport 1998/123, 24 pp.
Geologiske Undersøgelse Rapport 1998/123, 24 pp.
Authors' address
Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: lhn@geus.dk
Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: lhn@geus.dk
Fig. 3. The drilling of two deep wells at Margretheholm, central Copen-
hagen.
