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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
  • 304 Downloads

Abstract

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.

Keywords

Hydraulic fracturing Cyclic stimulation Pulsed stimulation Fatigue stimulation concepts Äspö HRL 

Abbreviations

AE

Acoustic emission

EGS

Enhanced geothermal system

EM

Electromagnetic

FBP

Formation breakdown pressure

HF

Hydrofracturing test

HRL

Hard rock laboratory

ISIP

Instantaneous shut-in pressure

M

Monitoring borehole

MF

Main frac

MS

Micro-seismic

RF

Refrac cycle

RFP

Refrac pressure

S1

Maximum principal stress

S2

Intermediate principal stress

S3

Minimum principal stress

Sh

Minimum horizontal stress

h

Interval length

k

Permeability

ln

Natural logarithm

q

Flow rate

qmean

Mean flow rate

t0

Injection time

Δt

Shut-in time

Vinj

Fluid volume injected

Vre

Fluid volume returned

α

Dip (with respect to horizontal)

β

Dip direction (north over east)

θ

Fracture strike direction (north over east)

μ

Dynamic viscosity of fluid

Notes

Acknowledgements

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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