GEORG Geothermal Workshop 2016 Presentation title: Mechanical and permeability properties of the Krafla reservoir lithology

1. MECHANICAL AND PERMEABILITY
PROPERTIES OF THE KRAFLA
RESERVOIR LITHOLOGY
Guðjón Helgi Eggertsson, Yan Lavallée,
Jackie E. Kendrick

2. “The exploitation of
magma may stand as the
next big step in
geothermal energy”

3. Magmatic hydrothermal systems
• Some key questions have
already (partly) been
answered, including:
 Can these fluids be
managed?
 Can we engineer a
sustainable system?
• These systems could:
 Have wells with several
times the output.
 Decrease the cost.
 Limit the visual impact.
(Picture source: Landsvirkjun)

4. 180-220°C
Hydrothermal reservoir
250-350°C
Conductive transition
Magma at >850°C
Caprock
Schematic picture of a magma/hydrothermal system
Heat
Heat
Well

5. 180-220°C
Hydrothermal reservoir
250-350°C
Fractured area => convection
Magma at >850°C
Caprock
Schematic picture of a magma/hydrothermal system
Heat
Heat
Well

6. Aims and
objectives To constrain
• the mechanics and permeability of intact
and fractured rocks at Krafla;
• the response of rocks in tensional
regimes such as induced by fracking or
thermal stimulation;
• the response of the different lithologies
to variable stresses and temperatures;
• the permeability of hot rocks.
To seek ways to control fluid flow in
the reservoir.
Better understanding
Better
results
Better
outcome

7. Method
Samples from 5 lithologies within Krafla caldera (6 rock types).
A large data set is needed to constrain these rocks.

8. Mechanical data
The data set will be expanded through tri-axial experiments.
(Eggertsson et. al., in prep)

9. Storage capacity - the rock porous network
• The impact of
a fracture
may not have
significant
effects on the
storage
capacity.
(Eggertsson et.al. in prep)

10. Permeability-porosity
• Porosity has strong
controls on permeability.
• The transition from pore-
dominated flow to fracture-
dominated flow is observed
at ~15% porosity.
• Some of the lithologies
show significant variability
in permeability and
porosity.
(Eggertsson et.al. in prep)

11. Permeability
• Permeability
may be
strongly
influenced by
the effective
pore pressure.
Intact sample of
gabbro
(Eggertsson et al., in prep)

12. Permeability
• A fracture may
change the
permeability by
1-5 orders of
magnitude.
(Eggertsson et al., in prep)
Fractured
sample of
ignimbrite
The hyaloclastite
was not able to
withhold a fracture.

13. Impact of a second fracture
(Eggertsson et al., 2016)
The impact of a
second fracture
is very small.
The samples range from fracture dominated (below
~15%) to pore dominated (above ~15%)
10.9% 12.9% 13.5%
14.8% 15.9% 21.3%

14. Further work
• How does temperature affect
the permeability of different
lithologies?
?

15. Further work
• How does temperature affect
the permeability of different
lithologies?
(Lamur et al. in prep)

16. Further work
• How does temperature affect
the permeability of different
lithologies?
• How does temperature affect
the rock properties?
(Coats et.al. in prep)

17. Further work
• How does temperature affect
the permeability of different
lithologies?
• How does temperature affect
the rock properties?
• What is the effect and rate of
mineral precipitation and
alteration?

18. Supporters:
:
THANK YOU
• E-mail: g.eggertsson@liverpool.ac.uk
Twitter: @GudjonHelgi

19. (Coats et.al. in prep)

20. Better understanding of
the physical rock
properties will ultimatly
lead to better
understanding and better
models of magmatic
hydrothermal systems.