Induced seismicity in Enhanced Geothermal Systems (EGS) in Alsace, France. Jean Schmittbuhl 1

Transcription

1 Induced seismicity in Enhanced Geothermal Systems (EGS) in Alsace, France Jean Schmittbuhl 1 Olivier Lengliné 1, Mohamed Boubacard 1, Lucie Lamourette 1, Lilas Vivin 1, Nicolas Cuenot 2 1 EOST-IPGS, Université de Strasbourg and CNRS, France 2 GEIE Exploitation Minière de la Chaleur, Kutzenhausen, France

2 Outline o Observations at Soultz-sous-Forêts 2010 circulation Variable stress drop within multiplets [Lengliné et al, JGR, 2014] o Observations at Rittershoffen (ECOGI) GRT1 stimulation Template matching technique for high resolution monitoring o Seismic and aseismic slip in the reservoir [Schmittbuhl et al, GE, 2015] 19/11/2015 IS-EPOS Katowice 2

3 The EGS pilot at Soultz-sous-Forêts (GEIE EMC) (1987- ) Binary geothermal power plant (ORC) 1.5 MWe net B 0m 1400m Pump Sediments Granite 5000m GPK1 GPK2 GPK3 GPK4 EGS Reservoir: 200 A complex pre-existing 3D network (granite) + a major fault zone (most of the seismicity) FZ-4770 in GPK3 Abundant natural fluid (high salinity (~100g/l) reservoir size? A Sausse et al, 2010 FZ-4770 GPK 1,2,3,(4) 19/11/2015 IS-EPOS Katowice 3

4 EGS stimulation and seismicity Target: significant permeability enhancement but with a limited seismicity A possible risk of felt EQ (if Ml > 2) 2000 : Ml max = : Ml max =2.9, : Ml max = : Ml max = km A tool for reservoir imaging 3 km 19/11/2015 IS-EPOS Katowice 4

5 Soultz-sous-Forêts GEIE EMC Hydraulic circulations in the lower reservoir (5 km) Circul. days Chem. Stim. GPK4 GPK4 Pump No sub pump Failure Failure Failure Soultz-sous-Forêts GEIE EMC Hydraulic circulations in the lower reservoir (5 km) 2 wells 1P, 1R 1P, 1R 1P, 1R 1P, 1R 3 wells 2P, 1R 2P, 1R 1P, 2R 1P, 2R 1P, 2R 1P, 2R 1P, 2R 4 wells 2P, 2R WHP R MPa 4 to 7 ~7 ~12 2 to 8 2 to 6 4 to 5 <2 <2 <1 Event & Mag Mx & Vol m /11/2015 R = reinjection IS-EPOS Katowice 5

6 2010 circulation test Production Injection 411 detected events, most intense activity when reinjection into GPK3 only Increase of activity at the end of the test, maybe due to the continuous rise of GPK3 injection pressure Remaining activity for 15 days after shut in 25 earthquakes of magnitude larger than 1 and 4 of magnitude larger than 2 - a series of 3 occurred within a few days - the M=2.3 occurred 4 months after Not linked with significant hydraulic event 19/11/2015 IS-EPOS Katowice 6

7 Soultz-sous-Forêts GEIE EMC Hydraulic circulations in the lower reservoir (5 km) Induced micro-seismicity activity at depth (Dec 2009 Aug 2010) Induced seismicity No induced seismicity In 2010: WH injection overpressure ~4.5 MPa, > 400 µseismic events In 2011: WH injection overpressure ~2.0 MPa, 5 µseismic events 19/11/2015 IS-EPOS Katowice 7

8 Data - Network Sampling frequency 150 Hz 8 surface, short-period seismometers Mostly vertical sensors Circulation experiment Water injected at 5 km depth Starting 01/01/ months long 411 detected earthquakes Automatic procedure M [ ] Manually reviewing all arrival times Localisation (393 events)

9 Similar Events Coherency > 90% at two stations Frequency range [10-40] Hz Windows of 1.7 s around P (256 pts long) Four groups with at least one M>1 earthquake # of events (19 /13 / 9 / 9)

10 Earthquake double difference relative relocation Cross-correlation P-wave travel times delays Projected on the inferred fracture plane Uncertainties computed from likelihood computed around the best solution 95 % ellipse Running window correlation to validate results S-P travel time delays Less than 3 ms delay for all groups at all stations Distance in the ray direction less than ~23 m 19/11/

11 Estimating absolute rupture size for the largest event of all groups using Brune s model Corner frequency f c [10-20] Hz uncertainties are quite important Rupture radius of m assuming a circular rupture patch Consistent with the estimated rupture size considering a typical stress drop of 1MPa

12 Comparison with closeby, «normal» earthquakes with the same magnitude. Certainly not an attenuation effect 19/11/2015 IS-EPOS Katowice 12

13 Variation of moment for events in a group Compare waveforms amplitude at similar stations Singular Value Decomposition Method [Rubinstein & Ellsworth, 2010] Stables moment variation estimates for similar events Up to a factor x 300 of moment variation for one group A x200 factor of amplitude variation 19/11/2015 IS-EPOS Katowice 13

14 [Allmann & Shearer, 2009] Seismic stress drop σ = Cμ D L Constant over a wide magnitude range of magnitude But deviations are noticed 19/11/

15 Interpretation Variation of seismic moment is interpreted as a variation of seismic slip Similarly it reflects a variation of seismic stress drop Implies a x300 variation of seismic stress drop on the same asperity 19/11/2015 IS-EPOS Katowice 15

16 Link with fluid injection Time history of the seismic slip on the 4 asperities 19/11/2015 IS-EPOS Katowice 16

17 Rittershoffen GRT1 GRT1: Drilling start Sept 26th, 2012 Drilling end Dec, 24th, 2012 Stimulation June 2013 target: 2500m ECOGI 19/11/2015 IS-EPOS Katowice 17

18 Seismological network Maurer et al., /11/2015 IS-EPOS Katowice 18

19 Temporal evolution Temporal evolution of seismicty 1st stage 2 nd stage 682 identified end picked seismic events Kaiser effet No seismicity for injection rate lower than previsously applied nd crisis High seismicity level 3.5 days after shut-in. No earthquake during this interval Number of events Evts/hr 19/11/2015 IS-EPOS Katowice 19

20 Template matching 2.5 seconds 4 hours 19/11/2015 IS-EPOS Katowice 20

21 Template matching KUHL.Z Time (s) Event number (chronological) 19/11/2015 IS-EPOS Katowice 21

22 Relocations N N W E W E 48.9 S 48.9 S Seiscomp - realtime km Manual detection km /11/2015 IS-EPOS Katowice 22

23 N N W E W E S S km km /11/2015 IS-EPOS Katowice 23

24 Cornet et al., 1997 Scholz, 1998 Reduced effective normal stress can even lead to slow aseismic movement aseismic slips already inferred in geothermal reservoirs [Cornet et al, 1997; Bourouis & Bernard, 2007] A good candidate for a transition area because of elevated temperature Possibly lower amplitude events (no borehole instrument operational at that time) 19/11/