Gunnar Gunnarsson, Reykjavik Energy, OR Iceland Geothermal Conference 2013 March 5-8, 2013, Harpa, Reykjavík

1. The geothermal reservoir and the development of
a new production eld in Hellisheiði
Gunnar Gunnarsson
Reykjavik Energy OR
IGC March 7, 2013

2. Introduction
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ISNET X [km]
0
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m y.s.
Bitra
Hverahlíð
Hellisheiði
Nesjavellir
Hengill
Reykjavík
The Hengill is a central
volcano.
Two production elds are in
the area: Nesjavellir
(120 MWe) and Hellisheiði
(303 MWe).
Nesjavellir Power Plant
commissioned in 1990. First
wells drilled in 1972 last
unit commissioned in 2005.
In Hellisheiði drilling started
in 2002, rst units were
commissioned 2006 and the
last in 2011.

3. The Hengill Area Surface exploration
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ISNET X [km]
0
200
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600
800
m y.s.
Bitra
Hverahlíð
Hellisheiði
Nesjavellir
Hengill
Reykjavík
The Hengill Area is a central
volcano Volcanic craters,
hot springs and fumaroles.

4. The Hengill Area Surface exploration
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
0
200
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600
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m y.s.
Bitra
Hverahlíð
Hellisheiði
Nesjavellir
Hengill
Reykjavík
The Hengill Area is a central
volcano Volcanic craters,
hot springs and fumaroles.
Highest degree of alteration
in the highest part of the
Hengill Mountains.

5. The Hengill Area Surface exploration
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
0
200
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600
800
m y.s.
Bitra
Hverahlíð
Hellisheiði
Nesjavellir
Hengill
Reykjavík
The Hengill Area is a central
volcano Volcanic craters,
hot springs and fumaroles.
Highest degree of alteration
in the highest part of the
Hengill Mountains.
Resistivity measurements
(TEM) show large area
where high resistivity core is
under low resistivity cap.

6. The Hengill Area Surface exploration
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
0
200
400
600
800
m y.s.
Bitra
Hverahlíð
Hellisheiði
Nesjavellir
Hengill
Reykjavík
The Hengill Area is a central
volcano Volcanic craters,
hot springs and fumaroles.
Highest degree of alteration
in the highest part of the
Hengill Mountains.
Resistivity measurements
(TEM) show large area
where high resistivity core is
under low resistivity cap.
Power estimates based on
resistivity survey.

7. Conceptual model of a Volcanic geothermal system

8. Old Conceptual model of the Hengill Area

9. The rst wells in Hellisheiði
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ISNET X [km]
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ISNET X [km]
0
200
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600
800
m y.s.
Bitra
Hverahlíð
Hellisheiði
Nesjavellir
Hengill
Reykjavík
He-04
He-07
He-03
He-06
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d[m]
HE−03
T [°C]
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d[m]
HE−04
T [°C]
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d[m]
HE−06
T [°C]
0
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1500
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2500
0 100 200 300
d[m]
HE−07
T [°C]

10. Formation temperature Hengill
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ISNET X [km]
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ISNET X [km]
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T [°C]
Form. temp. 500 m b.s.l.
Well data formation
temperature.
The formation temperature
unveils the thermodynamics
of the geothermal system.
The formation temperature
in the Hengill Area is
characterize by sharp
structures.
Hotter areas separated by
cooler ones separate heat
sources...
...or sharp changes in
permeability.

11. Formation temperature Hengill
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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T [°C]
Form. temp. 1000 m b.s.l.
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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T [°C]
Form. temp. 1500 m b.s.l.

12. Formation temperature in Hellisheiði
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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T [°C]
Form. temp. 500 m b.s.l.
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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T [°C]
Form. temp. 1500 m b.s.l.

13. Formation temperature in Hellisheiði
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HE−03
HE−04
HE−06
HE−07
HE−57
HE−36
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ISNETY[km]
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ISNET X [km]
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T [°C]
Form. temp. 1000 m b.s.l.
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d[m]
HE−03
T [°C]
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d[m]
HE−04
T [°C]
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d[m]
HE−06
T [°C]
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d[m]
HE−07
T [°C]
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d[m]
HE−36
T [°C]
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d[m]
HE−57
T [°C]

14. Formation temperature in Hellisheiði
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ISNETY[km]
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ISNET X [km]
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280
HE−26
Reykjafell
HE−10
HE−36
HN−01
HE−21
Gráuhnúkar
A
A’
B
B’
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ISNETY[km]
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ISNET X [km]
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T [°C]
Berghiti 1000 m u.s. 0
20
406080100120140160
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220
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300
−3000
−2000
−1000
0
1000
Elevationa.s.l.[m]
−2000 −1000 0 1000 2000
Position [m]
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300
T °C
HE−10
HE−26
Reykjafell
A A’
−20
0
20
406080100120140
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0
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Elevationa.s.l.[m]
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Position [m]
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300
T °C
HE−21
HE−36
HN−01
Gráuhnúkar
B B’

15. Formation temperature in the Hengill Area
Localized maxima in formation temperature cooler regions in
between. Sharp structures.
Reversed temperature gradient on the edge of the hottest
regions.
Separate heat sources drive the geothermal activity.
Older conceptual models that postulate a single heat source
under the highest part of the Hengill Mountains that drives the
geothermal elds in the Hengill Area are in contradiction with
observed distribution of formation temperature.
New conceptual model assume that the geothermal elds in
the area are driven by individual heat sources1.
1
Here a heat sources means the hot body that interacts to the water
circulation

16. The development of a eld and conceptual models
Conceptual models do evolve during the development of a
geothermal eld when new information become available.
This is why it has been postulated that geothermal operation
should be developed in steps.
All decisions on the size of the Hellisheiði Power Plant were
made before the data from the drilling operation became
available.
These decisions were based on limited information on the
initial state of the reservoir and no production history data.
Production in the Hellisheiði Field is concentrated on the
hottest part of the system.

17. Distribution of production
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ISNETN[km]
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ISNET A [km]
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ISNET A [km]
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ISNETN[km]
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ISNET A [km]
Distribution of the total mass production
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kg/s/km2
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ISNET A [km]
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ISNETN[km]
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ISNET A [km]
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ISNETN[km]
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ISNET A [km]
Distribution of the steam production
0
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300
kg/s/km2

18. Distribution of production playing with numbers
The mass production pro km2 is
300 kg/s/km2 in the center of
the production eld.
If no recharge drawdown in the
time interval ∆T is given by:
∆d =
Q
A
1
ρφ
∆T
If porosity is 10% and temperature
275◦C (ρ = 759 kg/m3)
drawdown in a year is:
∆d =
3 × 10−4 kg/m2/s
759 kg/m3
· 0.1
3.16 × 107
s
∆d = 125 m

19. Pressure drawdown Mass in and out
Drawdown is dependent on two
more important parameters.
Natural recharge (Qnr ) and
Reinjection (Qri ).
Drawdown taking those
parameters into account is given
by:
∆d =
Qp − Qnr − Qri
Aρφ
∆T.
Drawdown can be decreased by
reinjecting and spreading the
production.

20. Managing the reservoir reinjection
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ISNET X [km]
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ISNET X [km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNET X [km]
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ISNET X [km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
390
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ISNETY[km]
376 378 380 382 384 386 388
ISNET X [km]
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ISNETY[km]
376 378 380 382 384 386 388
ISNET X [km]
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ISNETY[km]
376 378 380 382 384 386 388
ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
376 378 380 382 384 386 388
ISNET X [km]
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ISNETY[km]
376 378 380 382 384 386 388
ISNET X [km]
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ISNETY[km]
376 378 380 382 384 386 388
ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
376 378 380 382 384 386 388
ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
H
e l l i s h e i ð i
H
úsm
úli
G
ráuhnúkar
Reykjavík
20 km
Reinjection zones of the
Hellisheiði Power Plant.
The Gráuhnúkar Reinjection
Zone commissioned in 2007
High formation
temperature ( 300◦C).
The Húsmúli Reinjection
Zone commissioned in 2011.
The Gráuhnúkar Zone
viewed as a possible zone
for make-up wells.

21. Pressure Drawdown in Hellisheiði
−40
−35
−30
−25
−20
−15
−10
−5
0
2000 2005 2010 2015 2020 2025 2030 2035 2040
Drawdown∆P[bar]
year
Pressure drawdown in well HE−04
Measured
Model
Reference

22. Future management of the Hellisheiði Field
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ISNETY[km]
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ISNET X [km]
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ISNETY[km]
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ISNET X [km]
100
150
200
250
300
T [°C]
Hverahlíð
H
ellisheiði
Gráuhnúkar
Húsmúli
Form. temp. 1000 m b.s.l.
The Hellisheiði Field is
narrow and needs to be
enlarged.
The Gráuhnúkar Zone
viewed as a possible zone
for make-up wells.
Injection supports the
pressure in the center of the
system.
Disposal of geothermal
water needs to be
addressed.
The Hverahlíð Field a new
production zone or make-up
zone for Hellisheiði?

23. Summary and conclusion
Surface exploration gives a limited information on the size and
state of the of the geothermal reservoir.
Direct measurements on the size of the reservoir rst become
available with exploratory drilling.
The development of the production eld in Hellisheiði was
undertaken in a very fast pace Decisions were often based on
limited information.
The production in the Hellisheiði Field is concentrated in a
narrow strip, where the density of production is very high.
Managing the production in the Hellisheiði Field will be a
challenge due to the high production rate per area.
It is desirable to enlarge the production area: Possible make-up
zones Gráuhnúkar and Hverahlíð.

24. Thank you for your attention.