The effect of fluid compressibility and elastic rock properties on deformation of geothermal reservoirs

• Published in: Geophysical Journal International
• Main Authors: Juncu, Daniel, Arnadottir, Thora, Geirsson, Halldor, Gunnarsson, Gunnar Th
• Other Authors: Jarðvísindastofnun (HÍ), Institute of Earth Sciences (UI), Verkfræði- og náttúruvísindasvið (HÍ), School of Engineering and Natural Sciences (UI), Háskóli Íslands, University of Iceland
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2019
• Subjects: Seismology; Creep and Deformation; Elasticity and Anelasticity; Geomechanics; Hydrothermal Systems; Jarðskjálftafræði; Jarðhitasvæði; Iceland
• Online Access: https://hdl.handle.net/20.500.11815/2053; https://doi.org/10.1093/gji/ggz011

Publsiher's version (útgefin grein) The characterization of magnetic minerals in rocks often uses methods that measure induced magnetization. When rocks, sediments or soils contain two magnetic phases, in which one has a high saturation magnetization (MS), for example magnetite, and the other a low MS, for example hematite, the induced magnetization will be dominated by the stronger phase. An earlier study by Frank and Nowaczyk has shown that even when magnetite makes up <10 wt per cent of the ferromagnetic content, it will mask hematite. This makes identification of phases with low MS difficult to identify. We conduct a systematic study of synthetic mixtures of single domain magnetite and hematite with a broad spectrum of particle size, using hysteresis properties, acquisition of isothermal remanent magnetization (IRM) and first-order reversal curve distributions (FORC). Hysteresis parameters and FORC distributions do not vary significantly from the pure magnetite sample for hematite concentrations =90 wt per cent. IRM is not saturated for hematite concentration of 30 wt per cent or higher. Principle component analysis (PCA) of the processed FORCs, detects the presence of hematite for concentrations 70 wt per cent at the very least. Our results illustrate the difficulty in identifying hematite when it is found together with magnetite. IRM acquisition is the most sensitive method for identifying hematite when it occurs together with magnetite. © 2019 The Author(s). We would like to thank Andrew Hooper (University of Leeds), Björn Lund (Uppsala University), Sigurjón Jónsson (King Abdullah University of Science and Technology), Ólafur Flóvenz (Iceland GeoSurvey) and Freysteinn Sigmundsson (University of Iceland) for their helpful comments on the manuscript. Comments from the editor (Michael Ritzwoller) and two anonymous reviewers were highly appreciated and helped to improve this paper. COMET is the NERC Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics. This work was ...