COTHERM-IPGT – Geological calibration of geophysical measurements for geothermal reservoir characterization

• Research unit: SFOE
• Project number: SI/500913

Key words (English)

geothermal reservoirs, geothermal, exploration, seismics, magneto-telluric, petrophysics

Short description (German)

Bei der geophysikalischen Charakterisierung tiefer geothermaler Reservoire von der Oberfläche aus überlagern sich Effekte von Geothermalwassergehalt, Temperatur, Porosität usw., die dadurch nicht separat erfasst werden können. Das Projekt kalibriert anhand eines heute erkalteten und durch Erosion zugänglich gewordenen Geothermalsystems in Island diese Überlagerung, um zu-künftige präzise Messungen in der geothermischen Exploration zu ermöglichen.

Short description (English)

In the geophysical characterization of deep geothermal reservoirs from the surface the effects of geothermal water content, temperature, porosity and others interfere and cannot separately be quantified. The project aims at calibrating this interference at the example of a fossil, now ex-posed geothermal reservoir in Iceland to allow accurate determination in future measurements for geothermal exploration.

Final report (English)

This MSc-thesis project is an investigation of petrophysical properties of a fossilised high-temperature hydrogeothermal system in Geitafell in the south-east of Iceland. It involved both laboratory determinations of elastic properties on small samples as well as in-situ measured seismic and electrical properties. The objective was to get actual field values on three profiles which started in intrusive material (old magma chamber, gabbro), continued to the transition zone (hornfels) and ended in the altered host rock (basalt) which was intersected by a decreasing number of dykes and sheets towards the end of the lines. Three other lines were chosen to yield information about the variations (different degrees of alteration) in the host rock. Data quality for all measurements was moderate (mainly due to poor contact between geophones/electrodes and the ground). Data pre-processing and inverse modeling were used to turn the measured data into the most reasonable images of subsurface structure. A high smoothing factor was applied to counter the under-determination nature of the inverse problem. The seismic arrival times needed to be corrected for static shift. As a result, ranges of P-wave velocities and resistivities could be extracted from subsurface models on the basis of several defined criteria. The P-wave velocities measured in the field were then compared to P-wave velocities at various pressures measured in the Rock Physics lab at ETH Zurich. These rock samples were collected from the field site in Geitafell and geochemical analysis showed that the differences in composition were minor. The determined velocities for both measurements are in good agreement with each other and the rather high velocity values can be attributed to low porosity. The small differences between the field and lab velocities can be explained by the different frequencies and length scales used in the measurements.

Auftragnehmer/Contractant/Contraente/Contractor:


Autorschaft/Auteurs/Autori/Authors:
Zuercher,Benjamin
Greenhalgh,Stewart

Related documents

• Alteration and petrology in a fossil hydrothermal system at Geitafell central volcano, Iceland, Master Thesis - Schlussbericht [PDF] 6'239 kB
• Petrophysical and geophysical field study of a fossilized hydrogeothermal system in Geitafell, Iceland, Master Thesis - Schlussbericht [PDF] 5'059 kB