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Journal Article

Long-Term Evolution of Fracture Permeability in Slate: An Experimental Study with Implications for Enhanced Geothermal Systems (EGS)

Authors
/persons/resource/chaojie

Cheng,  C.
4.8 Geoenergy, 4.0 Geosystems, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/hermi

Herrmann,  Johannes
4.2 Geomechanics and Scientific Drilling, 4.0 Geosystems, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Wagner,  Bianca
External Organizations;

Leiss,  Bernd
External Organizations;

/persons/resource/jessi

Stammeier,  Jessica Alexandra
3.1 Inorganic and Isotope Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/uddi

Rybacki,  Erik
4.2 Geomechanics and Scientific Drilling, 4.0 Geosystems, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/milsch

Milsch,  H.
4.8 Geoenergy, 4.0 Geosystems, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

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5008560.pdf
(Publisher version), 9MB

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Citation

Cheng, C., Herrmann, J., Wagner, B., Leiss, B., Stammeier, J. A., Rybacki, E., Milsch, H. (2021): Long-Term Evolution of Fracture Permeability in Slate: An Experimental Study with Implications for Enhanced Geothermal Systems (EGS). - Geosciences, 11, 11, 443.
https://doi.org/10.3390/geosciences11110443


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5008560
Abstract
The long-term sustainability of fractures within rocks determines whether it is reasonable to utilize such formations as potential EGS reservoirs. Representative for reservoirs in Variscan metamorphic rocks, three long-term (one month each) fracture permeability experiments on saw-cut slate core samples from the Hahnenklee well (Harz Mountains, Germany) were performed. The purpose was to investigate fracture permeability evolution at temperatures up to 90 °C using both deionized water (DI) and a 0.5 M NaCl solution as the pore fluid. Flow with DI resulted in a fracture permeability decline that is more pronounced at 90 °C, but permeability slightly increased with the NaCl fluid. Microstructural observations and analyses of the effluent composition suggest that fracture permeability evolution is governed by an interplay of free-face dissolution and pressure solution. It is concluded that newly introduced fractures may be subject to a certain permeability reduction due to pressure solution that is unlikely to be mitigated. However, long-term fracture permeability may be sustainable or even increase by free-face dissolution when the injection fluid possesses a certain (NaCl) salinity