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| Titel |
Seismic properties of fluid bearing formations in magmatic geothermal
systems: can we directly detect geothermal activity with seismic methods? |
| VerfasserIn |
Melchior Grab, Samuel Scott, Beatriz Quintal, Eva Caspari, Hansruedi Maurer, Stewart Greenhalgh |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250124072
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| Publikation (Nr.) |
 EGU/EGU2016-3443.pdf |
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| Zusammenfassung |
| Seismic methods are amongst the most common techniques to explore the earth’s subsurface.
Seismic properties such as velocities, impedance contrasts and attenuation enable
the characterization of the rocks in a geothermal system. The most important goal
of geothermal exploration, however, is to describe the enthalpy state of the pore
fluids, which act as the main transport medium for the geothermal heat, and to detect
permeable structures such as fracture networks, which control the movement of
these pore fluids in the subsurface. Since the quantities measured with seismic
methods are only indirectly related with the fluid state and the rock permeability,
the interpretation of seismic datasets is difficult and usually delivers ambiguous
results.
To help overcome this problem, we use a numerical modeling tool that quantifies the
seismic properties of fractured rock formations that are typically found in magmatic
geothermal systems. We incorporate the physics of the pore fluids, ranging from the liquid to
the boiling and ultimately vapor state. Furthermore, we consider the hydromechanics of
permeable structures at different scales from small cooling joints to large caldera faults as are
known to be present in volcanic systems.
Our modeling techniques simulate oscillatory compressibility and shear tests
and yield the P- and S-wave velocities and attenuation factors of fluid saturated
fractured rock volumes. To apply this modeling technique to realistic scenarios,
numerous input parameters need to be indentified. The properties of the rock matrix and
individual fractures were derived from extensive literature research including a large
number of laboratory-based studies. The geometries of fracture networks were
provided by structural geologists from their published studies of outcrops. Finally, the
physical properties of the pore fluid, ranging from those at ambient pressures and
temperatures up to the supercritical conditions, were taken from the fluid physics
literature.
The results of this study allow us to describe the seismic properties as a function of
hydrothermal and geological features. We use it in a forward seismic modeling study to
examine how the seismic response changes with temporally and/or spatially varying fluid
properties. |
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