Tectonic Seismogenic Index of Geothermal Reservoirs

Transcription

1 Tectonic Seismogenic Index of Geothermal Reservoirs C. Dinske 1, F. Wenzel 2 and S.A. Shapiro 1 1 Freie Universität Berlin 2 KIT Karlsruhe November 27, 2012

2 Introduction M max reservoir location -2.0 Barnett Shale -1.2 Cotton Valley 2.3 Soultz Basel 3.7 Cooper Basin 4.3 Paradox Valley

3 Introduction M max reservoir location -2.0 Barnett Shale -1.2 Cotton Valley 2.3 Soultz Basel 3.7 Cooper Basin 4.3 Paradox Valley What are the physical principles describing the magnitude distribution? What are the controlling factors of magnitudes of fluid-induced seismicity? Can we elaborate a model to evaluate the seismic hazard by fluid injections and to mitigate the occurrence of large (felt) events?

4 Introduction - Magnitude Distribution of Induced Events physical model: combination of Darcy law and continuity equation (principle of mass conservation) (nonlinear) diffusion of pore pressure perturbation event number N is proportional to the cumulative injected fluid mass m c : N m c V I geothermal reservoirs: Basel (M = 0.7) Soultz (M = 1.2) hydrocarbon reservoirs: Barnett Shale (M = 2.9) Cotton Valley (M = 2.1) magnitude-frequency distribution obeys a Gutenberg-Richter probability: log 10 N M = constant + log 10 V I b M

5 Introduction - the constant: Seismogenic Index Σ describes the seismotectonic state at an injection site combines four (generally unknown) site-specific parameters: ( ) ζ constant = a + log 10 Σ C max S fracture bulk concentration ζ, poroelastic modulus S, maximum critical pressures C max, a value of Gutenberg-Richter probability location (type) Basel (2006/EGS) 0.4 Cooper (2003/EGS) -0.9 Ogachi (1991/EGS) -2.6 Ogachi (1993/EGS) -3.2 Soultz (1993/EGS) -2.0 Soultz (1995/EGS) -3.8 Soultz (1996/EGS) -3.1 Soultz (2000/EGS) -0.5 KTB (1994/SCI) KTB ( /SCI) -4.2 Paradox ( /WD) -2.6 Unterhaching (HYD) -5.0 Barnett Shale (FRAC) -9.2 Cotton V. A (FRAC) -6.2 Cotton V. B (FRAC) -4.4 Cotton V. C (FRAC) -9.4 Canada, BC, A (FRAC) -2.9 Canada, BC, B (FRAC) -2.3 Canada, BC, C (FRAC) -3.5 Australia (FRAC) -8.0 Σ

6 Significance of Seismogenic Index expected number of events with a given minimum magnitude: N M = V I 10 Σ b M occurrence probability of an event with a given magnitude: P(0, M, V I ) = exp( V I 10 Σ bm ) implementation in real-time monitoring: Σ & b

7 Motivation How can we evaluate a potential seismic hazard prior to development / hydraulic stimulation of a reservoir?

8 Motivation How can we evaluate a potential seismic hazard prior to development / hydraulic stimulation of a reservoir? 1. collect a database based on observations from different types of reservoirs (different geological and tectonical settings), analysis of parameterization and correlations of seismogenic index) application to undeveloped reservoir sites 2. use tectonic seismic activity in order to evaluate the seismotectonic state of an area where fluid injections are planned seismogenic index for tectonic seismicity Σ tec

9 Seismogenic Index: Correlations 1 - CC CC CC CC CC PGA (tectonic seismicity): GSHAP hazard map [Giardini et al., 2003] 2. depth of stimulated reservoir and induced seismicity 3. b value of the frequency magnitude distribution 4. cumulative seismic moment release 5. seismic energy normalised to hydraulic energy

10 Seismogenic Index: Continuing Work How can we evaluate a potential seismic hazard prior to development / hydraulic stimulation of a reservoir? 1. collect a database based on observations from different types of reservoirs, in different geological and tectonical settings (including analysis of parameterization and correlations of seismogenic index) application to undeveloped reservoir sites 2. use tectonic seismic activity in order to evaluate the seismotectonic state of an area where fluid injections are planned seismogenic index for tectonic seismicity Σ tec

11 Fluid-Induced Seismicity Tectonic Seismicity fractures and faults with bulk concentration ζ tec contained in a rock volume fractures are characterised by critical (shear stress) values C necessary for activation of shear slip continuous but slow perturbation of stress resulting from tectonic deformation an earthquake occurs along a fracture if shear stress exceeds local criticality value σ 3 seismogenic volume V tec with fault concentration ζ tec σ 1 σ 1 shear slip event at fracture location if accumulated shear stress τ will be larger than critical value C σ 3

12 Tectonic Seismogenic Index event rate R is proportional to the shear stress rate τ = G ǫ in a given seismogenic volume V tec : R = Gζ tec C maxtec ǫv tec G: shear modulus ζ tec: bulk concentration of pre-existing fractures 1/C maxtec : probability density function of critical shear stresses event rate R Mtec with magnitude larger than M: R M = Gζ tec C maxtec ǫv tec 10 a bm combine the unknown quantities to the seismogenic index Σ tec : ( ) Gζtec Σ tec a + log 10 = log 10 R M log 10 ( ǫ V tec ) + b M C maxtec

13 Work-flow: (I) Estimation of Seismicity Parameters 1. Search available earthquake databases 2. Define a seismogenic volume based on the spatial distribution of earthquakes and limiting accordingly the catalogue 3. Process the EQ catalogue: - Decluster in order to identify and remove aftershocks - Define a completeness level 4. Determine the b value from the frequency-magnitude distribution 5. Compute the annual probability of a given magnitude earthquake

14 Work-flow: (I) Estimation of Seismicity Parameters 1. Search available earthquake databases 2. Define a seismogenic volume based on the spatial distribution of earthquakes and limiting accordingly the catalogue 3. Process the EQ catalogue: - Decluster in order to identify and remove aftershocks - Define a completeness level 4. Determine the b value from the frequency-magnitude distribution 5. Compute the annual probability of a given magnitude earthquake

15 Work-flow: (I) Estimation of Seismicity Parameters 1. Search available earthquake databases 2. Define a seismogenic volume based on the spatial distribution of earthquakes and limiting accordingly the catalogue 3. Process the EQ catalogue: Decluster in order to identify and remove aftershocks - Define a completeness level 4. Determine the b value from the frequency-magnitude distribution 5. Compute the annual probability of a given magnitude earthquake

16 Work-flow: (I) Estimation of Seismicity Parameters 1. Search available earthquake databases 2. Define a seismogenic volume based on the spatial distribution of earthquakes and limiting accordingly the catalogue 3. Process the EQ catalogue: Decluster in order to identify and remove aftershocks Define a completeness level 4. Determine the b value from the frequency-magnitude distribution 5. Compute the annual probability of a given magnitude earthquake

17 Work-flow: (I) Estimation of Seismicity Parameters 1. Search available earthquake databases 2. Define a seismogenic volume based on the spatial distribution of earthquakes and limiting accordingly the catalogue 3. Process the EQ catalogue: Decluster in order to identify and remove aftershocks Define a completeness level 4. Determine the b value from the frequency-magnitude distribution 5. Compute the annual probability of a given magnitude earthquake

18 Work-flow: (I) Estimation of Seismicity Parameters 1. Search available earthquake databases 2. Define a seismogenic volume based on the spatial distribution of earthquakes and limiting accordingly the catalogue 3. Process the EQ catalogue: Decluster in order to identify and remove aftershocks Define a completeness level 4. Determine the b value from the frequency-magnitude distribution 5. Compute the annual probability of a given magnitude earthquake

19 Work-flow: (II) Estimation of Strain Rates deformation strain rates ǫ can be calculated from geodetic measurements (i.e. GPS, displacement) use published results: Basel & Soultz - [Tesauro et al., 2005] Ogachi - [Hasegawa et al., 2005] Paradox Valley - [Blume and Sheehan, 2003] and [Chang et al., 2006] seismic strain rates can be calculated from the seismic moment provided by the earthquake magnitudes [Kostrov, 1974; Molnar, 1983] use published results: Basel - [Delacou et al., 2004] application of the approach to reservoir locations in the Upper Rhine Graben seismicity parameters - [Burkhard and Grünthal, 2009] deformation strain rates - [Tesauro et al., 2005]

20 Tectonic Seismogenic Index Σ tec = log 10 R Mtec log 10 ( ǫ V tec ) + b M Location M Event b Strain Seismogenic Σ tec Σ inj Rate [ 1 yr ] Rate [ 1 yr ] Volume [m3 ] Basel Basel Soultz to -0.5 Ogachi to -2.7 Ogachi to -2.7 Ogachi to -2.7 Ogachi to -2.7 Paradox V Paradox V Rhine Graben Rhine Graben up to two units difference

21 Comparison of Seismogenic Indices seismogenic index for tectonic seismicity is slightly smaller than seismogenic index for fluid-induced seismicity at a given location Σ inj Σ tec = ( ainj a tec ) ( ) ( ) ( ) ζinj Cmaxtec 1 + log 10 + log 10 + log 10 ζ tec C maxinj S G regional (averaged) versus local values of a, ζ and C max S Pa 1 and G Pa difference of 0.5 different stressing rates: stress changes due to fluid injection occur rather instantaneous compared to the slow tectonic loading seismic strain approximately 1/100 of tectonic strain [Kostrov, 1974]

22 Conclusions number of fluid-induced earthquakes increases proportional to the injected fluid mass site-specific, seismotectonic parameters control their frequency-magnitude statistics seismogenic index quantifies the seismotectonic state of a reservoir this index permits to compute the occurrence probability of a given magnitude event strategies to evaluate potential seismic hazard prior to reservoir development: correlations between seismogenic index and known parameters seismogenic index based on tectonic seismicity the tectonic seismogenic index can be used as a proxy of the seismogenic index for fluid-induced seismicity contributes to site selection and injection design

23 Acknowledgments Data are kindly provided by: Basel: M. Häring Cooper Basin: H. Kaieda Ogachi: H. Kaieda Soultz: A. Jupe (courtesy of G.E.I.E.) Paradox Valley: K. Mahrer Barnett Shale: S. Maxwell Cotton Valley: J. Rutledge Unterhaching: J. Wassermann and by sponsors of the PHASE research project. EQ catalog data were processed using ZMAP [Wiemer, 2001].

24 Blume, F. and Sheehan, A. F. (2003). Quantifying seismic hazard in the southern Rocky Mountains through GPS measurements of crustal deformation. In Boyer, D., Santi, P., and Rogers, W., editors, Engineering Geology in Colorado: Contributions, Trends, and Case Histories, volume 55. Colorado Geological Survey. Burkhard, M. and Grünthal, G. (2009). Seismic source zone characterization for the seismic hazard assessment project PEGASOS by the Expert Group 2 (EG1b). Swiss J Geosciences, 102:doi: /s Chang, W.-L., Smith, R. B., Meertens, C. M., and Harris, R. A. (2006). Contemporary deformation of the Wasatch fault, Utah, from GPS measurements with implications for interseismic fault behavior and earthquake hazard: Observations and kinematic analysis. J Geophys Res, 111:doi: /2006JB Delacou, B., Sue, C., Champagnac, J.-D., and Burkhard, M. (2004). Present-day geodynamics in the bend of the western and central Alps as constrained by earthquake analysis. Geophys J Int, 158:doi: /j X x. Giardini, D., Grünthal, G., Shedlock, K. M., and Zhang, P. (2003). International Handbook of Earthquake & Engineering Seismology, volume 81 of International Geophysics Series, chapter The GSHAP Global Seismic Hazard Map, pages Academic Press, Amsterdam. Hasegawa, A., Nakajima, J., Umino, N., and Miura, S. (2005). Deep structure of the northeastern Japan arc and its implications for crustal deformation and shallow seismic activity. Tectonophysics, 403:doi: /j.tecto Tesauro, M., Hollenstein, C., Egli, R., Geiger, A., and Kahle, H.-G. (2005).

25 Continuous GPS and broad-scale deformation across the Rhine Graben and the Alps. Int J Earth Sci, 94:doi: /s Wiemer, S. (2001). A software package to analyze seismicity: ZMAP. Seism Res Letters, 72:doi: /gssrl