Response of Upper Jurassic (Malm) Limestone to Temperature Change: Experimental Results on Rock Deformation and Permeabi
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ORIGINAL PAPER
Response of Upper Jurassic (Malm) Limestone to Temperature Change: Experimental Results on Rock Deformation and Permeability Liang Pei1,2 · Guido Blöcher1 · Harald Milsch1 · Günter Zimmermann1 · Ingo Sass3 · Xiaochun Li2 · Ernst Huenges1 Received: 19 September 2019 / Accepted: 5 October 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract The present study aimed to quantify the thermally induced deformation and the associated evolution of permeability in Blaubeuren limestone, an outcrop analogue of the Upper Jurassic (Malm) carbonate formation, providing references for hydro-thermo-mechanical responses of the reservoir rock to temperature changes within future enhanced geothermal systems as located in the Southern German Molasse Basin. Experiments deriving the changes in the primary (water-accessible) pore volume and the bulk volume of three water-saturated rock samples were conducted via loading the samples to defined stress states ( 𝜎3 of 15 MPa; 𝜎1 of up to 75 MPa ), respectively, and then cycling sample temperature between 30 °C and defined levels up to 120 °C at a sustained pore pressure of 0.5 MPa. Permeability was measured under isothermal conditions at each attained temperature. The primary voids dilated upon heating and partly contracted via cooling in each applied temperature cycle yielding thereby residual dilation. However, the concomitant bulk sample deformation manifested residual compaction. The permeability increased with increasing temperature and showed residual decreases by the end of the temperature cycling tests. Flow of pore fluid from the primary voids into the secondary voids at increased temperatures due to the decreased fluid viscosity mimicked irreversible dilation in the primary voids. The interplay between pressure solution-driven compaction and thermal expansion in rock solids was considered to account for the sample deformation and the development of permeability. It is presumable that the pressure solution-driven compaction and the contraction in rock solids would influence the long-term hydro-thermo-mechanical behavior of the Upper Jurassic carbonate reservoir rocks in the cooling process related to fluid injection at the geothermal systems located therein. Keyword Thermal expansion · Irreversible deformation · Pressure solution · Porosity · Permeability · Limestone List of Symbols THMC Thermo-hydro-mechanical- and chemical-coupled process EGS Enhanced geothermal systems SEM Scanning electron microscopy Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00603-020-02270-5) contains supplementary material, which is available to authorized users. * Liang Pei [email protected] 1
Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ, Telegrafenberg, 14473 Potsdam, Germany
2
Wuhan Institute of Rock and Soil Mechanics, Chinese Academy of Science, Xiaohongshan 430071, Wuhan, People’s Republic of China
3
Institute for Applied Geosciences, Technical University Darmstadt, 64287
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