Research ArticleEARTH SCIENCES

Controlling fluid-induced seismicity during a 6.1-km-deep geothermal stimulation in Finland

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Science Advances  01 May 2019:
Vol. 5, no. 5, eaav7224
DOI: 10.1126/sciadv.aav7224
  • Fig. 1 Schematic view of the project site (see fig. S1 for a map view).

    The location of stimulation stages S1 to S5 into the bottom open hole section and basic stimulation parameters are shown in the inset.

  • Fig. 2 Evolution of seismic source and statistical properties of induced seismicity in response to fluid injection.

    Temporal evolution of double-difference relocated seismicity (n = 1977) plotted as the distance from the bottom of OTN-3 and color-encoded by stimulation phase (A). Well-head pressure and cumulative injection per stimulation subphase are shown as solid red and dark blue lines, respectively. (B) Gutenberg-Richter (GR) b-value changes (magenta dots). The evolution of seismic event rate calculated for all events above magnitude of completeness and for a catalog with MW > −0.5 is shown in gray and superposed black line, respectively. (C) Moment (MW) and local Helsinki magnitudes (MLHEL) of seismic events. Events detected but not located are shown as black points (note day-night detection level variations).

  • Fig. 3 Induced seismicity hypocenters during stimulation campaign.

    (A) Map view and (B) SW-NE depth section showing double-difference relocated seismicity (n = 1977) color-coded with stimulation phase. Injection stages S1 to S5 are colored accordingly from the bottom of the open hole (6.4 km MD) toward the casing shoe (5.4 km MD) of OTN-3. The size of each event is proportional to the moment magnitude.

  • Fig. 4 Evolution of seismic moment, radiated energy and hydraulic energy release during stimulation.

    (A) Cumulative seismic moment release with time. (B) Cumulative radiated seismic energy release as a function of hydraulic energy. (C) Seismic injection efficiency IE changes with time.

  • Fig. 5 Temporal evolution of maximum observed seismic moment versus cumulative volume of injected fluid at each phase (P1 to P5).

    Colored circles are from various injection projects (8, 19, 20). Maximum magnitude estimates using different models are shown with solid, dashed, and dotted lines (8, 10, 15). The γ and b parameter values used in (8, 10) were calculated after the stimulation, assuming geomechanical and seismic parameters from this study, and plotted for comparison with the observed evolution of seismic moment (see Materials and Methods).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/5/eaav7224/DC1

    Fig. S1. Location of St1 Deep Heat Oy project site and different seismic networks used to monitor the stimulation campaign.

    Fig. S2. Optimized velocity model for P and S waves (black and red lines, respectively), initially compiled from borehole logs.

    Fig. S3. Key time intervals indicating changes in pumping protocols (Roman numerals) together with pressure and cumulative injection per injection subphase (see Materials and Methods for detailed description of changes in pumping protocol).

    Fig. S4. b-value distribution for the full catalog.

    Fig. S5. Results of declustering analysis.

    Fig. S6. Dependence between corner frequency and seismic moment for the group of 56 earthquakes with MW between 0.9 and 1.9, for which spectral parameters have been estimated using the spectral fitting method.

    Text S1. Access to catalog data

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Location of St1 Deep Heat Oy project site and different seismic networks used to monitor the stimulation campaign.
    • Fig. S2. Optimized velocity model for P and S waves (black and red lines, respectively), initially compiled from borehole logs.
    • Fig. S3. Key time intervals indicating changes in pumping protocols (Roman numerals) together with pressure and cumulative injection per injection subphase (see Materials and Methods for detailed description of changes in pumping protocol).
    • Fig. S4. b-value distribution for the full catalog.
    • Fig. S5. Results of declustering analysis.
    • Fig. S6. Dependence between corner frequency and seismic moment for the group of 56 earthquakes with MW between 0.9 and 1.9, for which spectral parameters have been estimated using the spectral fitting method.
    • Text S1. Access to catalog data

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