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Geologic controls on supercritical geothermal resources above magmatic intrusions.

Scott S, Driesner T, Weis P - Nat Commun (2015)

Bottom Line: Conventional high-enthalpy resources result from mixing of ascending supercritical and cooler surrounding water.Our models reproduce the measured thermal conditions of the resource discovered at Krafla.Similar resources may be widespread below conventional high-enthalpy geothermal systems.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth Sciences, Institute of Geochemistry and Petrology, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland.

ABSTRACT
A new and economically attractive type of geothermal resource was recently discovered in the Krafla volcanic system, Iceland, consisting of supercritical water at 450 °C immediately above a 2-km deep magma body. Although utilizing such supercritical resources could multiply power production from geothermal wells, the abundance, location and size of similar resources are undefined. Here we present the first numerical simulations of supercritical geothermal resource formation, showing that they are an integral part of magma-driven geothermal systems. Potentially exploitable resources form in rocks with a brittle-ductile transition temperature higher than 450 °C, such as basalt. Water temperatures and enthalpies can exceed 400 °C and 3 MJ kg(-1), depending on host rock permeability. Conventional high-enthalpy resources result from mixing of ascending supercritical and cooler surrounding water. Our models reproduce the measured thermal conditions of the resource discovered at Krafla. Similar resources may be widespread below conventional high-enthalpy geothermal systems.

No MeSH data available.


The formation of supercritical water resources depends on geologic controls.(a). Typical large-scale thermal structure of a simulated geothermal system, showing the fluid phase state distribution, temperature contours (black lines), fluid pressure contours (blue lines), potentially exploitable supercritical water resources (red areas, defined as fluid with temperature and specific enthalpy greater than 374 °C and 2.086 MJ kg−1, respectively, in host rock with a permeability >10−16 m2) as well as the impermeable intrusion (single-phase vapour at a permeability <10−16 m2, grey). Zones of two-phase (liquid and vapour) coexistence are shown in blue, and single-phase vapour at a temperature below the critical temperature is shown in green. The finite element grid, consisting of ∼10,000 triangular elements in a domain 5 and 15 km in horizontal and vertical extent, is also shown. (b–g). Snapshots of the area near the top of the intrusion (black box in a), under different conditions of host rock permeability (ko) and brittle–ductile transition temperature (TBDT). Liquid (grey) and vapour (black) flow vectors are also shown (not to scale between different fluid phases or simulations). We vary ko from 10−14 m2 (b,d,f) to 10−15 m2 (c,e,g) and vary TBDT from 360 °C (b,c), to 450 °C (d,e), and 550 °C (f,g).
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f1: The formation of supercritical water resources depends on geologic controls.(a). Typical large-scale thermal structure of a simulated geothermal system, showing the fluid phase state distribution, temperature contours (black lines), fluid pressure contours (blue lines), potentially exploitable supercritical water resources (red areas, defined as fluid with temperature and specific enthalpy greater than 374 °C and 2.086 MJ kg−1, respectively, in host rock with a permeability >10−16 m2) as well as the impermeable intrusion (single-phase vapour at a permeability <10−16 m2, grey). Zones of two-phase (liquid and vapour) coexistence are shown in blue, and single-phase vapour at a temperature below the critical temperature is shown in green. The finite element grid, consisting of ∼10,000 triangular elements in a domain 5 and 15 km in horizontal and vertical extent, is also shown. (b–g). Snapshots of the area near the top of the intrusion (black box in a), under different conditions of host rock permeability (ko) and brittle–ductile transition temperature (TBDT). Liquid (grey) and vapour (black) flow vectors are also shown (not to scale between different fluid phases or simulations). We vary ko from 10−14 m2 (b,d,f) to 10−15 m2 (c,e,g) and vary TBDT from 360 °C (b,c), to 450 °C (d,e), and 550 °C (f,g).

Mentions: The key control on the formation of supercritical resources is the brittle–ductile transition temperature TBDT. Extensive supercritical water resources can develop if TBDT is at least 450 °C (Fig. 1d,e). Increasing TBDT from 450 to 550 °C results in somewhat larger supercritical zones without dramatically changing the thermo-hydraulic conditions of such reservoirs (Fig. 1f,g). For TBDT<450 °C (for example, 360 °C, Fig. 1b,c) only minor supercritical resources develop because the threshold permeability is encountered at temperatures slightly higher than the critical temperature of water.


Geologic controls on supercritical geothermal resources above magmatic intrusions.

Scott S, Driesner T, Weis P - Nat Commun (2015)

The formation of supercritical water resources depends on geologic controls.(a). Typical large-scale thermal structure of a simulated geothermal system, showing the fluid phase state distribution, temperature contours (black lines), fluid pressure contours (blue lines), potentially exploitable supercritical water resources (red areas, defined as fluid with temperature and specific enthalpy greater than 374 °C and 2.086 MJ kg−1, respectively, in host rock with a permeability >10−16 m2) as well as the impermeable intrusion (single-phase vapour at a permeability <10−16 m2, grey). Zones of two-phase (liquid and vapour) coexistence are shown in blue, and single-phase vapour at a temperature below the critical temperature is shown in green. The finite element grid, consisting of ∼10,000 triangular elements in a domain 5 and 15 km in horizontal and vertical extent, is also shown. (b–g). Snapshots of the area near the top of the intrusion (black box in a), under different conditions of host rock permeability (ko) and brittle–ductile transition temperature (TBDT). Liquid (grey) and vapour (black) flow vectors are also shown (not to scale between different fluid phases or simulations). We vary ko from 10−14 m2 (b,d,f) to 10−15 m2 (c,e,g) and vary TBDT from 360 °C (b,c), to 450 °C (d,e), and 550 °C (f,g).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4525172&req=5

f1: The formation of supercritical water resources depends on geologic controls.(a). Typical large-scale thermal structure of a simulated geothermal system, showing the fluid phase state distribution, temperature contours (black lines), fluid pressure contours (blue lines), potentially exploitable supercritical water resources (red areas, defined as fluid with temperature and specific enthalpy greater than 374 °C and 2.086 MJ kg−1, respectively, in host rock with a permeability >10−16 m2) as well as the impermeable intrusion (single-phase vapour at a permeability <10−16 m2, grey). Zones of two-phase (liquid and vapour) coexistence are shown in blue, and single-phase vapour at a temperature below the critical temperature is shown in green. The finite element grid, consisting of ∼10,000 triangular elements in a domain 5 and 15 km in horizontal and vertical extent, is also shown. (b–g). Snapshots of the area near the top of the intrusion (black box in a), under different conditions of host rock permeability (ko) and brittle–ductile transition temperature (TBDT). Liquid (grey) and vapour (black) flow vectors are also shown (not to scale between different fluid phases or simulations). We vary ko from 10−14 m2 (b,d,f) to 10−15 m2 (c,e,g) and vary TBDT from 360 °C (b,c), to 450 °C (d,e), and 550 °C (f,g).
Mentions: The key control on the formation of supercritical resources is the brittle–ductile transition temperature TBDT. Extensive supercritical water resources can develop if TBDT is at least 450 °C (Fig. 1d,e). Increasing TBDT from 450 to 550 °C results in somewhat larger supercritical zones without dramatically changing the thermo-hydraulic conditions of such reservoirs (Fig. 1f,g). For TBDT<450 °C (for example, 360 °C, Fig. 1b,c) only minor supercritical resources develop because the threshold permeability is encountered at temperatures slightly higher than the critical temperature of water.

Bottom Line: Conventional high-enthalpy resources result from mixing of ascending supercritical and cooler surrounding water.Our models reproduce the measured thermal conditions of the resource discovered at Krafla.Similar resources may be widespread below conventional high-enthalpy geothermal systems.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth Sciences, Institute of Geochemistry and Petrology, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland.

ABSTRACT
A new and economically attractive type of geothermal resource was recently discovered in the Krafla volcanic system, Iceland, consisting of supercritical water at 450 °C immediately above a 2-km deep magma body. Although utilizing such supercritical resources could multiply power production from geothermal wells, the abundance, location and size of similar resources are undefined. Here we present the first numerical simulations of supercritical geothermal resource formation, showing that they are an integral part of magma-driven geothermal systems. Potentially exploitable resources form in rocks with a brittle-ductile transition temperature higher than 450 °C, such as basalt. Water temperatures and enthalpies can exceed 400 °C and 3 MJ kg(-1), depending on host rock permeability. Conventional high-enthalpy resources result from mixing of ascending supercritical and cooler surrounding water. Our models reproduce the measured thermal conditions of the resource discovered at Krafla. Similar resources may be widespread below conventional high-enthalpy geothermal systems.

No MeSH data available.