Permeability Enhancement and Fracture Development of Hydraulic In Situ Experiments in the Äspö Hard Rock Laboratory, Sweden

  • Günter Zimmermann
  • Arno Zang
  • Ove Stephansson
  • Gerd Klee
  • Hana Semiková
Original Paper


A new advanced protocol of progressively increased cyclic injection and pulsed injection design for hydraulic fracturing experiments was implemented at 410 m depth in the Äspö Hard Rock Laboratory in Sweden. A monitoring array was installed around the tested horizontal borehole to detect the acoustic emissions and micro-seismic events during the fracturing process. The aim is to identify optimized injection schemes to reduce the seismicity related to the fracturing processes. The cyclic stimulation scheme of loading and unloading the fracturing net pressure leads to a lower accompanied seismicity if compared to the conventional hydraulic fracturing with constant flow rates. The related permeability of the tested rock interval can be increased, but this increase is less pronounced than that of the conventional treatments and, especially, if compared to the last of the re-fracturing series with high seismicity increase. Despite these limitations, in field applications with expected high risk of unwanted seismic events, this advanced protocol can be a feasible option to reduce this risk.


Hydraulic fracturing Cyclic stimulation Pulsed stimulation Fatigue stimulation concepts Äspö HRL 



Acoustic emission


Enhanced geothermal system




Formation breakdown pressure


Hydrofracturing test


Hard rock laboratory


Instantaneous shut-in pressure


Monitoring borehole


Main frac




Refrac cycle


Refrac pressure


Maximum principal stress


Intermediate principal stress


Minimum principal stress


Minimum horizontal stress


Interval length




Natural logarithm


Flow rate


Mean flow rate


Injection time


Shut-in time


Fluid volume injected


Fluid volume returned


Dip (with respect to horizontal)


Dip direction (north over east)


Fracture strike direction (north over east)


Dynamic viscosity of fluid



The geothermal project described in this manuscript was financially supported by GFZ German Research Center for Geosciences, Potsdam (75%), KIT Karlsruhe Institute of Technology (15%) and Nova Center for University Studies, Research and Development, Oskarshamn, Sweden (10%). An additional in-kind contribution of SKB for using Äspö Hard Rock Laboratory as test site for geothermal research is greatly acknowledged. The assistance of Felix Becker (MeSy-Solexperts, Bochum) and O. Vanecek and J. Skalova (ISATech, Prague) in performing the hydraulic field tests is greatly appreciated.


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Copyright information

© Springer-Verlag GmbH Austria, part of Springer Nature 2018

Authors and Affiliations

  • Günter Zimmermann
    • 1
  • Arno Zang
    • 1
  • Ove Stephansson
    • 1
  • Gerd Klee
    • 2
  • Hana Semiková
    • 3
  1. 1.Helmholtz-Zentrum Potsdam-Deutsches GeoForschungsZentrum GFZPotsdamGermany
  2. 2.MeSy-Solexperts GmbHBochumGermany
  3. 3.ISATech s.r.o.Prague 7Czech Republic

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