An analysis of well temperature data and geothermal gradients provide insights for onshore geothermal opportunities as well as highlighting areas of recent hydrocarbon charge on the Norwegian Continental Shelf (NCS). Higher gradients (> 40 degrees C/km) have been identified in a number of areas including; Southern North Sea Salt Diapirs, the Utsira High, the Peon Discovery, the Western Møre and Vøring Basins. Area of higher gradients are often coincident with areas of recent (Neogene to Quaternary) hydrocarbon charge and fluid movement along significant vertical conduits such as salt diapirs, basement faults, dykes and hydrothermal vents. Many oil accumulations in these areas are associated with anomalously low biodegradation due to recent rapid charge. Repeated ice sheet loading and unloading has resulted in very recent uplift, erosion, tilting, trap breach, fluid migration and fluid remigration and subsurface temperature changes. Further analysis is proposed to determine the relative importance of conductive versus convective/advective heat flow and the influence of ice sheet loading and unloading has had on recent fluid and heat flow paths and subsurface temperature changes.

1. Geothermal Energy and Ice
an unlikely alliance?
Insights from temperature data
on the Norwegian Continental Shelf
Ciaran Nolan
August 2021

2. Summary
• Temperature data from 1385 exploration wells on the Norwegian Continental
Shelf (NCS) highlights areas of high geothermal gradients (> 40 oC/km).
• The data provides insights into the influence of recent ice sheet loading and
unloading on convective/advective heat flow and it’s control on present day
basin temperatures.
• The data provides insights for onshore geothermal opportunities that have
been influenced by ice, as well as highlighting areas of recent hydrocarbon
charge on the NCS.
NCS Bottom Hole Temperatures
Norwegian Continental Shelf Basins and
Wells with Bottom Hole Temperatures

3. Geothermal Regimes
Conductive v Advective Heat Flow
• There is an ongoing debate as to the relative importance and
contribution of conductive versus convective/advective heat
flow as outlined by Jessop et al1.
• For example Sheldon et al2 evaluated 93 oil and gas wells and
33 water wells in the North Perth Basin, Australia and
established convection as the dominant force.
• The geothermal regime in a basin is controlled by the
magnitude and interaction of various heat sources and transfer
mechanisms.
• Heat generation;
– Heat flowing from the mantle
– Heat generated internally in the crust via decay of
radioactive isotopes
• Heat transfer
– Conduction via the rocks
– Convection and advection via fluids

4. Norwegian Continental Shelf
1385 exploration wells with temperature data
North Sea Mid Norway Barents Sea
N

5. Norwegian Continental Shelf
Variation in Geothermal Gradient
North Sea Mid Norway Barents Sea
Hot / Cold
A
Colour fill maps range from 25 (blue) – 55 (red) OC/km. Areas
of higher geothermal gradients (>40 OC/km) include;
A. Southern North Sea Salt Diapirs
B. North Sea - Utsira High
C. Stord Basin / Troll
D. Peon Discovery
E. Western Møre and Vøring Basins
F. Outer Trøndelag Platform
G. Wisting Area
H. Hammerfest Basin
I. Vestbakken Volcanic province
B
D E
G
N
F
C
H
I
Gro Discovery

6. NPD
Bottom Hole Temperature (BHT) estimate
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
m
TVD
bsfl
Temperature
(°C)
• Focus of this study is on large scale regional trends
• CAUTION - the data has been screened but no horner corrections have been applied
• The NPD approach to calculation of BHTs is outlined below.
• Estimation of BHT is done using a second order polynomial fit to the available
measured temperatures from a well. Both wire line BHT's and DST temperatures are
used, but where DST temperatures are available the wire line bht's are omitted.
• If no data are available from the lower 500 m in a well, no temperature estimate is
given for that well.
• The diagram opposite illustrates standard procedure for a well.
• The uppermost data point, at sea floor, is usually set to 5°C. The data point at
(15.6°C, 165 m bsfl) is from the Peon. Discovery re-entry 35/2-1 R, a very shallow
well temperature measurement. This data point has been used since the Peon data
became available in 2006.
• In water depths exceeding 600 m the sea floor temperature is set to -0.5 °C and the
Peon data point is not used. The blue line show final TD in the well, and the
intersection between the polynomial fit (thin blue line) and TD give the estimated
"bottom hole temperature“.

7. QC of Temperature Data
• Calculation of geothermal gradient allows screening of
NPD temperature data and depth data
• Ongoing process
• A small number of errors have been observed so far and
reported to the NPD

8. Norwegian Continental Shelf
Temperature Data
• 1385 of the 1960 exploration wells have temperature data that meet
the screening and quality control criteria
• Mean geothermal gradients have been calculated for the 1385 wells
and gridded for the North Sea, Mid Norway and the Barents Sea
• The overall P90-P50-P10 geothermal gradient is 26-35-41 oC/km
• 6603/12-1 (Gro Discovery) has established the highest geothermal
gradient on the NCS - 59OC/km.

9. Variation in NCS Geothermal Gradients
Conclusions
1. Geothermal gradients have been calculated for 1385 wells in the NCS. The P90-P50-P10 geothermal gradient is 26-35-41 oC/km
2. Higher gradients (> 40 oC/km) have been identified in a number of areas including; Southern North Sea Salt Diapirs, the Utsira
High, the Peon Discovery, the Western Møre and Vøring Basins.
3. The Gro Discovery in the Western Møre Basin established the highest geothermal gradient on the NCS - 59OC/km. Early Paleocene
intrusions and associated hydrothermal vent complexes are prevalent in the area3,4. Evidence4 exists for hydrothermal and thermogenic
fluid flow above the vent complexes in Neogene to Quaternary times. The mechanism for Neogene to Quaternary reactivation is not
understood but may be related to the formation of the domes such as the Modgunn Arch which could be related to differential loading of
a Pliocene–Pleistocene glacial wedge5.
4. A trap and charge model6 that involves a pre existing trap (Motel) that has leaked, may explain the recent fluid migration along the edges
of shallow salt diapirs into shallower reservoirs as a consequence of loading and unloading of glacial ice in the last 0.5M years.
5. Higher gradients occur in shallow sections (<700m) of basins7 with high recent sediment rates followed by uplift and erosion – such as
Quaternary glaciogenic outwash fan sediments of the Peon gas discovery.
6. The oil fields of the Utsira High display a strong a correlation with higher geothermal gradients. In the SW Utsira high a rhenium-osmium
isotopic study suggests the main oil charge phase from the Viking Graben is very recent and potentially ongoing8. A study on the impact
of glacial loading and unloading9 suggests a reorganization of migration routes into the Utsira High due to Quaternary ice related tilting.
7. Area of higher gradients are often coincident with areas of recent (Neogene to Quaternary) hydrocarbon charge and fluid
movement along significant vertical conduits such as salt diapirs, basement faults, dykes and hydrothermal vents. Many oil
accumulations in these areas are associated with anomalously low biodegradation due to recent rapid charge.
8. Repeated ice sheet loading and unloading has resulted in very recent uplift, erosion, tilting, trap breach, fluid migration and
fluid remigration and subsurface temperature changes.
9. Further analysis is proposed to determine the relative importance of conductive versus convective/advective heat flow and the
influence of ice sheet loading and unloading has had on recent fluid and heat flow paths and subsurface temperature changes .
The observations provide insights for onshore geothermal opportunities as well as highlighting areas of recent hydrocarbon
charge on the NCS.

10. Norwegian Continental Shelf
Variations in Geothermal Gradients
North Sea Geothermal Gradient Mid Norway Geothermal Gradient Barents Sea Geothermal Gradient
A
B
D
E
E
G
H
Hot / Cold Hot / Cold
Hot / Cold
C
F
A. Southern North Sea Salt Diapirs
B. North Sea - Utsira High
C. Stord Basin / Troll
D. Peon Discovery
E. Western Møre and Vøring Basins
F. Outer Trøndelag Platform
G. Wisting Area
H. Hammerfest Basin
I. Vestbakken Volcanic province
I

11. 1. North Sea

12. North Sea
Mean Geothermal Gradient
• 1006 of the 1385 wells with temperature
(BHT) data that are in the North Sea
• P10-P50-P90 geothermal gradient is
26-34-41oC/km
• Four areas have been identified with
moderate to high gradients;
A. Salt diapirs in the southern north sea
B. Utsira High – Johan Sverdrup & Edvard Grieg
C. Stord Basin and Troll area
D. Peon Discovery
Geothermal Gradient – Colour Fill
A
B
D
C

13. Norwegian Continental Shelf
North Sea Geothermal Gradient
Basins and Structural Elements Geothermal Gradient
Central
Graben
Viking
Graben
A
B
D
Colour fill maps range from 25 (blue) – 50 (red) OC/km.
Areas of higher geothermal gradients include;
A. Southern North Sea Salt Diapirs
B. Utsira High
C. Stord Basin / Troll
D. Peon
Utsira
High
Åsta
Graben
Egersund
Basin
Danish
Norwegian
Basin
Stavanger
Platform
Stord
Basin
Tampen
Spur
C

14. North Sea
Importance of ice on recent fluid and heat flow
Figure 2 from Medvedev et al6
Computed vertical displacements
in the North Sea lithosphere
caused by: (a) ice loading; (b)
glacial erosion and (c) removing
the sediments of 2.5 Ma and
younger. The positive values of
displacements correspond to: (a)
downwards motion during ice-cap
development and upwards motion
during melting of the ice cap; (b)
upwards motion during erosion;
and (c) downwards motion during
sediment accumulation
• Medvedev et al.9 highlights the impact loading and unloading of ice in the last 2.5 Ma has had on
uplift, erosion, tilting, trap breach, fluid migration and fluid remigration on parts of the
Norwegian North Sea including the Utsira High.
A
B
D
A. Salt Diapirs
B. Utsira High
C. Stord Basin
D. Peon Discovery
C

15. 1. North Sea
a. Salt Diapirs

16. Southern North Sea - Norway
Distribution of Salt Diapirs
Basins and Structural Elements – Depth to Top Salt Selected Wells
Legend
Shallow salt diapir
(<2200m)
Deep salt diapir
(>2000m)
• Salt diapirs shown with colour fill, field outlines - no
colour fill.
• Shallow diapirs with a crest less than 2200m
shown in blue, deeper diapirs in red.
• 1/6-5, 2/7-12 and 2/8-13 wells were drilled in crestal
locations on three of the shallowest salt diapirs.
• A number of shallow to moderate depth salt diapirs
have evidence for recent oil and gas breaching.
• For example Oselvar 1/3-4 took a kick in the Middle
Miocene at 1595m and recovered 100 liters of
unbiodegraded 34O API oil while logging.
Oda
1/6-5
2/7-12
2/8-13
Valhall
Flyndre
Oselvar
1/3-4

17. Southern North Sea - Norway
Salt Diapirs and Geothermal Gradient
Geothermal Gradient – Colour Fill
Oda
59OC/km
1/6-5
56OC/km
2/7-12
48OC/km
2/8-13
49OC/km
Legend
Shallow salt diapir
(<2200m)
Deep salt diapir
(>2000m)
• Salt diapirs shown with blue and red cross hatch
• Shallow diapirs with crests <2000m shown in red
cross hatching
• Note the correspondence between shallow
diapirs and high geothermal gradients.
• Also note the low geothermal gradients between salt
diapirs within the salt withdrawal synclines.
• 1/6-5, 2/7-12 and 2/8-13 wells drilled on the crest of
three of the shallowest salt diapirs.
• All three wells encountered oil and gas above the salt
diapirs at shallow depths of burial (<1500m).
• In nearly all cases oil has not been biodegraded
suggesting relatively recent migration.
Oselvar
1/3-4

18. Southern North Sea - Norway
2/8-13 Salt Diapir
• Objective of Tertiary sands and Cretaceous chalk over the
salt diapir.
• Top Zechstein at 1775m.
• Gas/oil chimney above the diapir.
• Shallow gas was encountered at the prognosed depths, and
controlled with heavy mud. Shallow gas encountered in
sands at 828 m, caused the well to flow. The flow was killed
with heavy mud.
• One core was cut from 1780 m to 1782 m in the Zechstein
(Celestite section) with poor reservoir quality. Good oil shows
were recorded on the core.
• After having cut the core, the well became unstable and was
killed and cemented back to 1415 m and an unintentional
sidetrack was made.
• BHT of 96OC at 1940m TD, geothermal gradient of
49OC/km.
2/8-13
49OC/km

19. Southern North Sea Salt Diapirs
1/6-5 Salt Diapir
• 1/6-5 was drilled on the crest of a major salt diapir between the
Flyndre and Tommeliten
• Oil shows were first observed at 1434 and 1585 m, both in thin
limestone beds of Oligocene age. On reaching the top Ekofisk
Formation at 1721 m, limestone with oil stain and bright yellow
fluorescence was observed.
• Despite the abnormally high pressures and temperatures
encountered, drilling proceeded without major incidents. A
minor salt water flow accompanied by a 37.1 % gas peak
occurred during a trip at core point at 1725 m. The mud weight
was increased from 15 ppg to 15.3 ppg and finally 15.5 ppg as
a result of this flow.
• One DST was performed in the Cenomanian from 1722 to
1741 m. The well flowed 1450 bbls/day of water at a
temperature of 98OC.
• Geothermal gradient of 56OC/km.
1/6-5
56OC/km

20. Modelling of thermal and fluid system structure
near a passively growing salt diapir14
• Salt has exceptionally high thermal conductivity of 6 to 7 W/mK,
two to three times that of shale, sands and limestones resulting in
elevated geothermal gradients above salt diapirs (the so called
salt chimney effect).
• The advective role played by fluids flow in the surrounding basins
is less well understood, Canova et al14 modelled the thermal and
fluid system structure near a passively growing salt diapir.
• These temperature distributions are controlled by thermal
conduction through the salt and enveloping sediments and by
advecting warm waters near the salt and in the adjacent mini
basins.
• Systematic, depth-dependent permeability results in heat
being advected up the diapir in a narrower zone, with
increased flow at the diapir margin, this phenomenon is
affected by thermal input and salt dissolution from the
adjacent diapir. Cold waters are advected deeper into the
basin, and the salt chimney effect is dominated by advection.

21. Southern North Sea - Denmark
Lille John Salt Diapir6
• Goffey et al6 outline a trap and charge model (illustrated in Figure 22 above from the paper) for the Lille John salt
diapir in Denmark that is applicable to the salt diapirs throughout the Southern North Sea in Norway.
• The model involves a pre existing trap (Motel) that has leaked into shallower reservoirs as a consequence of the
loading and unloading of glacial ice in the last 500,000 years.
• The recent loading and unloading of glacial ice recent has increased the advective movement of warmer
fluids from deeper levels along the edges of the diapirs into shallow levels and contributed to the elevated
geothermal gradients observed at shallow diapirs in the Southern North Sea.

22. 1. North Sea
b. Utsira High
c. Stord Basin

23. North Sea - Utsira High and Stord Basin
Structural Elements and Geothermal Gradient
Basins and Structural Elements Geothermal Gradient – Colour Fill Geothermal Gradient – Colour Fill – Utsira High
The Utsira High - highlighted in yellow on the map above -
has geothermal gradients of 41-55OC/km, 5-10 OC/km higher
than the surrounding basins. Note the close
correspondence between the distribution of fields and the
higher geothermal gradients over the Utsira high.
Utsira
High
Viking
Graben
Johan
Svedrup
Ivar
Aasen
Balder
Grane
Ringhorne
Solveig
Edvard
Greig
Stord
Basin
Stord
Basin
Stord
Basin
The Stord Basin covers
a large area, however
only a few wells have
reliable temperature
data with geothermal
gradients close to
40OC/km – close to the
P10 range. The higher
gradients are partly a
gridding artefact of the
limited dataset. Further
well and temperature
data are required to
determine the true
nature of the geothermal
gradients in the basin.

24. NW
SE
Geothermal Gradient – Colour Fill – Utsira High
Johan
Svedrup
Ivar
Aasen
Balder
Grane
Ringhorne
Solveig
North Sea - Utsira High
Geothermal Gradient and Geoseismic Section
Geoseismic Section over the Utsira High*
The geoseismic section above is from Figure 1 of a paper10 by Osagiede et al illustrates the
shallow depths of crystalline basement in the Utsira High (<3km) and the correspondence
with elevated geothermal gradients of 41-55OC/km. The crystalline basement includes
granodioritic, gneissic, granitic, gabbroic, quartzitic, and phyllitic rocks of Silurian –
Devonian ages. These relatively acidic basement assemblage generates more radioactive
heat than mafic rocks.
However not all areas of shallow basement on the Utsira High are associated with
higher geothermal gradients.
SE
NW
Edvard
Greig
2km

25. North Sea- Southern Utsira High
Geothermal Gradient and Depth to Top Basement
• Not all areas of shallow basement on the Utsira High are
associated with higher geothermal gradients.
• The inset map on the left plots the depths to Top
Basement in the southern wells
• Note the three dry holes with shallow basement depths
of 1901 - 2860m TVDSS area correspond with moderate
to low geothermal gradients (purple to light green)
• Is there an alternative explanation to high conductive
heat flow to explain the elevated geothermal
gradients on the Utsira High ?
16/4-1
16/5-1
16/6-1
Johan
Svedrup
Solveig
Edvard
Greig

26. North Sea - Utsira High
Evidence for very recent charge and fluid flow
• Georgiev et al8 uses Re-Os dating to determine the timing of oil
charge at the Solveig field in the SW Utsira. The data supports two
phases of oil charge;
39+/- 23Ma (secondary, older biodegraded)
<1.2Ma (main – younger lighter oil)
• The main phase of charge (and mixing with older oil phase) is
potentially ongoing today.
NW
Geothermal Gradient – Colour Fill – Utsira High
Johan
Svedrup
Ivar
Aasen
Solveig
Edvard
Greig
Two main pulses of oil generation predicted by the
burial models during the Eocene–Miocene and the
Pliocene–Quaternary. Modelled oil generation rates
in red.
Areas of recent oil charge into Utsira
high are coincident with higher
geothermal gradients.

27. North Sea - Utsira High
BCU displacements caused by ice sheet processes
BCU vertical displacements
caused by: (a) surface
processes (b) the compaction
of sediments between the BCU
and basement loading of the
Quaternary layer; and (c)
combination of (a) and (b). The
positive displacements show
areas where the BCU is
shallower now than at 2.5 Ma.
Black lines outline major (>20
km2) the red line outlined in
white indicates the Utsira High.
• Medvedev et al.9 postulate Quaternary (<2.5 Ma) ice-sheet processes have resulted in very recent uplift, erosion,
tilting and modification of North Sea field hydrocarbon contacts.
• In their model the Utsira High fields (including Johan Sverdrup) have been very recently charged as a direct
result of ice sheet related modifications to hydrocarbon migration pathways from the Viking Graben.

28. 1. North Sea
d. Peon

29. North Sea
Peon – Geothermal Gradient
• Two Shallow wells (35/2-1 and 35/2-2) with TDs at 713 and 640m
• Large shallow gas deposit 100km west or Norway (Florø) within Quaternary
glaciogenic outwash fan sediments. 35 GSm³ gas in place
• Top reservoir 165m below seabed (at 384m) – reservoir temperature 15.6°C. ROV
seabed temperature 6.4 °C. Geothermal gradient = 56OC/km. Small inaccuracies
in shallow temperature readings can result in large errors in shallow gradients.
• Surrounding deep wells have normal gradients.
• Higher geothermal gradients are typical in shallow section (<700m) of basins with
high recent sediment rates followed up uplift and erosion as outlined by Nagihara,
and Smith11
*Regional overview of
deep sedimentary
thermal gradients of
the geopressured
zone of the Texas–
Louisiana continental
shelf January
2008AAPG Bulletin
92(1):1-14
Geothermal Gradient – Peon Area

30. Peon
Seismic Section and Well Log*
• Higher geothermal gradients are typical in the
shallow sections of basins (<700m) with high
recent sediment rates followed up uplift and
erosion as outlined by Nagihara and Smith11
• Medvedev et al9 estimate glacial isostatic
uplift and erosion of around 300m in the Peon
area.
• Figure 2 opposite from Bellwald et al12

31. Mid Norway
d) Western Møre and Vøring Basins
e) Outer Trøndelag Platform

32. Mid Norway
Mean Geothermal Gradient
• 276 of the 1385 wells with
temperature (BHT) data that are in
Mid Norway area
• P10-P50-P90 geothermal gradient
is
32-36-43 oC/km
a. High gradients in the Western Møre and
Vøring Basins
b. Moderate gradients in the outer Trøndelag
Platform
•
Geothermal Gradient – Colour Fill
Vøring
Basin
Møre
Basin
Møre
Marginal
High
(MMH)
Vøring
Marginal
High
(MMH)
Ormen
Lange
Trøndelag
Platform
Froan
Basin
D
E

33. Geothermal Gradient – Colour Fill
Taken from Figure 5 Ritter et al13
• Ritter et al13 document in situ temperature and heat flow were determined in 1994 at 159 sites in the Vøring
basin. High heat flow observed from surface sediments of the Vøring Marginal High the result of thermal
refraction into high conductivity volcanics and/or water flow along faults of the Vøring Escarpment.
• Note also the shallow nature of the crystalline basement (E) in the Outer Trøndelag Platform and
correspondence with elevated geothermal gradients.
Mid Norway
Mean Geothermal Gradient and Geoseismic
Vøring
Basin
Møre
Basin
Møre
Marginal
High
(MMH)
Vøring
Marginal
High
(MMH)
Ormen
Lange
Trøndelag
Platform
Froan
Basin
X
Y
D
E
E
D
X Y

34. Western Møre and Vøring Basins
6604/5-1 (Baldebrå) and 6603/12-1 (Gro) Wells
Geothermal Gradient – Colour Fill
West – East seismic section above from Chiarella et al15 (courtesy of TGS).
6604/5-1 (Baldebrå) encountered gas in Cretaceous Springar sands with a geothermal gradient of
51OC/km. To the south 6603/12-1 (Gro) encountered a 15m gas column in Cretaceous Springar
sands. The water temperature at seafloor, measured by ROV, was -1OC. A horner corrected
temperature of 139O C at 2335m TVD below sea floor, equates to a geothermal gradient of
59OC/km, a record in the NCS.
Highlighted in yellow are hydrothermal vent complexes associated with the sill and dyke
complexes (outlined by the red events).
W E
W E
6603/12-1
Gro
6604/5-1
Baldebrå

35. Basins and Structural Elements
Western Møre and Vøring Basins
Distribution of Intrusions and Hydrothermal Vent Complexes
Distribution of Intrusions & Hydrothermal Vent
Complexes (HVC)*
Vøring
Basin
Møre
Basin
The map on left highlights in pink the
extent of intrusions (dated 55-58Ma**) in
the Møre and Vøring Basins. The map on
the right from Planke et al3 highlights the
distribution of intrusions (colour coded by
depth yellow, orange and brown) and
hydrothermal vent complexes (circles and
triangles).
Roelofse et al4 emphasizes the importance
of intrusions and vents as long lasting and
in some cases ongoing conduits for hot
hydrothermal fluid flow to shallower strata.
The seeps originating from the intrusions
and vents often contain hydrocarbons that
can feed chemosynthetic communities
that can result in cold, deepwater corals.
Møre
Marginal
High
(MMH)
Vøring
Marginal
High
(MMH)
Ormen
Lange
Trøndelag
Platform
Froan
Basin

36. Western Møre and Vøring Basins
Evidence for fluid leakage above Hydrothermal Vent Complexes
Figure 10 from Roelofse et al4 a) Map view of the laterally
restricted high-amplitude anomaly overlying a dome HTVC; (b)
seismic section showing the HTVC and amplitude anomaly; c)
map view showing the location of a) and (b), and the distribution of
high-amplitude anomalies within 100 ms TWT above the Top Tare
Formation (H3), this is shown in (b). Some of the high-amplitude
anomalies are local and located above HTVCs, whilst others are
more extensive, likely due to lithological changes.

37. Western Møre and Vøring Basins
Hydrothermal Vent Complexes
Figure 12 above from Roelofse et al4. During the Miocene fluid migration along basement faults, sills and
HTVCs, which may explain the presence of high-amplitude anomalies in Eocene-Miocene strata (as shown
previously). These fluids will have added local heat to the upper crust to fossilise the Opal A-CT
boundary along the Modgunn Arch

38. Mid Norway – Mean Geothermal Gradient
Geothermal Gradient – Colour Fill
Distribution of Sills & Hydrothermal Vent Complexes
Vøring
Basin
Møre
Basin
Møre
Marginal
High
(MMH)
Vøring
Marginal
High
(MMH)
Ormen
Lange
Trøndelag
Platform
Froan
Basin
The map on the right Planke et al3
highlights the distribution of intrusions
(colour coded by depth yellow, orange
and brown) and hydrothermal vent
complexes (circles and triangles).Note
the correspondence between shallow
intrusions (yellow), hydrothermal vent
complexes (circles and triangles) and
higher geothermal gradients in the
Western Møre and Vøring Basins
adjacent to the Marginal Highs.
The intrusions and vents act as long
lasting and in some cases ongoing
conduits for hot hydrothermal fluid
flow to shallower strata that may
help explain the significantly
elevated geothermal gradients along
the Western Møre and Vøring Basins
adjacent to the Marginal Highs.

39. Barents Sea

40. Barents Sea – Mean Geothermal Gradient
• Much smaller dataset - 111 of the 1385
wells with temperature data in Barents
Sea covering a wide area.
• P10-P50-P90 geothermal gradient is
32-36-43 oC/km
• Three areas have been identified with
moderate to high gradients;
G. Wisting
H. Hammerfest Basin
I. Vestbakken Volcanic province
Geothermal Gradient – Colour Fill
G
H
I

41. Barents Sea – Mean Geotherm Gradient
Basins and Structural Elements Geothermal Gradient – Colour Fill
Hammerfest
Basin
Hoop Fault
Complex Nordkaap
Basin
Vestbakken
Volcanic
province
Loppa High
Wisting
7120/12-2
Alke Nord
7316/5-1
Three areas have been identified with moderate to high gradients;
G. Wisting
H. Hammerfest Basin - 7120/12-2 Alke Nord
I. Vestbakken Volcanic province - 7316/5-1
G
H
I

42. Barents Sea
Vestbakken Volcanic province
• Section and map from Figure 3b and 1 from a paper by Gac et al16
• 7316/5-1 has a TD temperature of 183OC that equates to a geothermal gradient of 50OC/km
• 7316/5-1 drilled close to the continent-ocean boundaries (COB – red dashed line on above seismic line
from
• Numerous igneous intrusions were penetrated below 2976 m (Middle to Early Eocene level) throughout the
well to TD. The intrusions were from 5 to 44 m thick.
• Eocene gas bearing sand at 1340m MD with net pay of 10m.
• Similarities with Western Møre and Vøring Basins

43. Wisting Discovery
• Sections above from OMV presentation by Stueland17
• Geothermal gradients vary over the Wisting Discoveries (37-52 oC/km)
• Very shallow Jurassic Stø Formation reservoir - 250m below the seabed
• API of 36O with only slight biodegradation
• Triassic Anisian Steinkobbe Formation source proven, possibility of secondary Jurassic source
component
• Barents Sea has experienced multiple episodes of widespread erosion in Cenozoic times. Early
Eocene-Miocene tectonic uplift resulted in the first major erosion phase followed by significant Pliocene-
Pleistocene glacial erosion
• Light oil with little biodegradation indicates very recent charge or deeper trap (Motel) that has
been breached during Pliocene-Pleistocene glacial uplift and erosion.

44. Conclusions

45. Variation in NCS Geothermal Gradients
Conclusions
1. Geothermal gradients have been calculated for 1385 wells in the NCS. The P90-P50-P10 geothermal gradient is 26-35-41 oC/km
2. Higher gradients (> 40 oC/km) have been identified in a number of areas including; Southern North Sea Salt Diapirs, the Utsira
High, the Peon Discovery, the Western Møre and Vøring Basins.
3. The Gro Discovery in the Western Møre Basin established the highest geothermal gradient on the NCS - 59OC/km. Early Paleocene
intrusions and associated hydrothermal vent complexes are prevalent in the area6. Evidence7 exists for hydrothermal and thermogenic
fluid flow above the vent complexes in Neogene to Quaternary times. The mechanism for Neogene to Quaternary reactivation is not
understood but may be related to the formation of the domes such as the Modgunn Arch which could be related to differential loading of
a Pliocene–Pleistocene glacial wedge.
4. A trap and charge model3 that involves a pre existing trap (Motel) that has leaked, may explain the recent fluid migration along the edges
of shallow salt diapirs into shallower reservoirs as a consequence of loading and unloading of glacial ice in the last 0.5M years.
5. Higher gradients occur in shallow sections (<700m) of basins4 with high recent sediment rates followed by uplift and erosion – such as
Quaternary glaciogenic outwash fan sediments of the Peon gas discovery.
6. The oil fields of the Utsira High display a strong a correlation with higher geothermal gradients. In the SW Utsira high a rhenium-osmium
isotopic study suggests the main oil charge phase from the Viking Graben is very recent and potentially ongoing8. Medvedev et al5
suggest a reorganization of the migration routes into the Utsira High due to Quaternary ice related tilting.
7. Area of higher gradients are often coincident with areas of recent (Neogene to Quaternary) hydrocarbon charge and fluid
movement along significant vertical conduits such as salt diapirs, basement faults, dykes and hydrothermal vents. Many oil
accumulations in these areas are associated with anomalously low biodegradation due to recent rapid charge.
8. Repeated ice sheet loading and unloading has resulted in very recent uplift, erosion, tilting, trap breach, fluid migration and
fluid remigration and subsurface temperature changes3.
9. Further analysis is proposed to determine the relative importance of conductive versus convective/advective heat flow and the
influence of ice sheet loading and unloading has had on recent fluid and heat flow paths and subsurface temperature changes .
The observations provide insights for onshore geothermal opportunities as well as highlighting areas of recent hydrocarbon
charge on the NCS.

46. References

47. References
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