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MECHANICAL AND PERMEABILITY PROPERTIES OF
THE KRAFLA RESERVOIR LITHOLOGY
Guðjón Helgi Eggertsson, Yan Lavallée, Jackie E. Kendrick
“The exploitation of magma may stand as the next big step in geothermal energy”
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)
180-220°CHydrothermal reservoir
250-350°C
Conductive transition
Magma at >850°C
Caprock
Schematic picture of a magma/hydrothermal system
Hea
t
Hea
t
Well
180-220°CHydrothermal reservoir
250-350°C
Fractured area => convection
Magma at >850°C
Caprock
Schematic picture of a magma/hydrothermal system
Hea
t
Hea
t
Well
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
MethodSamples from 5 lithologies within Krafla caldera (6 rock types).
A large data set is needed to constrain these rocks.
Mechanical data
The data set will be expanded through tri-axial experiments.
(Eggertsson et. al., in prep)
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)
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)
Permeability
• Permeability may be strongly influenced by the effective pore pressure. Intact sample
of gabbro
(Eggertsson et al., in prep)
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.
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%
Further work• How does temperature affect the permeability of different lithologies? ?
Further work• How does temperature affect the permeability of different lithologies?
(Lamur et al. in prep)
Further work• How does temperature affect the permeability of different lithologies?
• How does temperature affect the rock properties?
(Coats et.al. in prep)
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?
(Coats et.al. in prep)
Better understanding of the physical rock
properties will ultimatly lead to better
understanding and better models of magmatic
hydrothermal systems.
