Passive seismic monitoring for CO2 storage sites - Anna Stork, University of Bristol at UKCCSRC specialist meeting Geophysical modelling for CO2 storage, monitoring and appraisal, 3 November 2015
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The document discusses the risks and monitoring techniques associated with geomechanical deformation in CO2 storage sites. It highlights the potential effects of reservoir inflation on flow properties, the risk of caprock fracturing, and the possibility of induced seismicity. The document emphasizes the importance of passive seismic monitoring and provides examples from major carbon capture and storage (CCS) projects like Weyburn, In Salah, and Aquistore.
Passive seismic monitoring for CO2 storage sites - Anna Stork, University of Bristol at UKCCSRC specialist meeting Geophysical modelling for CO2 storage, monitoring and appraisal, 3 November 2015
- 1. Passive Seismic Monitoring of CO2 Storage Sites Anna L. Stork1, James P. Verdon1, J.-‐Michael Kendall1 , Claire Allmark2, Andrew Cur@s2 and Don J. White3 [email protected] UKCCSRC Geophysical modelling for CO2 storage, monitoring and appraisal mee@ng Leeds 3 November 2015 2 November 2015 1. University of Bristol 2. University of Edinburgh 3. Geological Survey Canada
- 2. Passive seismic monitoring 2 2 November 2015 will not pose a risk to storage security. However, if deformation becomes more substantial, it can affect storage operations in a number of ways, illustrated schematically in Fig. 1. The prin- cipal risks posed by geomechanical deformation to secure storage are summarized below. Reservoir Inflation and Alteration of Flow Properties. Pore pressure increase and inflation can influence the flow properties of a storage reservoir. Laboratory experiments show that perme- ability is sensitive to pressure (15). Furthermore, pore pressure increases may open existing fracture networks in the reservoir, or create new ones, along which CO2 can flow more rapidly. Per- meability increases within the reservoir will not pose a direct leakage risk. Nevertheless, if permeability is increased during injection, this will reduce the accuracy of fluid flow simulations used to predict the resulting CO2 distribution. The result may be that CO2 reaches spill-points or breaks through at other wells faster than anticipated, reducing the amount of CO2 that can be stored. For example, Bissell et al. (16) have shown that injectivity at In Salah is pressure dependent, implying that CO2 flow is controlled at least in part by the opening and closing of fractures in the reservoir. Fracturing of Sealing Caprocks. Deformation in a reservoir is generally transferred into the surrounding rocks. This can lead to the creation or reactivation of fracture networks around and above a reservoir. Fractures running through an otherwise impermeable caprock could compromise the storage integrity, providing permeable pathways for CO2 to escape from the reservoir. This is probably the greatest risk to storage security posed by geomechanical deformation. Leakage of gas through fractured caprock has been observed above hydrocarbon res- ervoirs (17, 18) and at natural gas storage sites (19). Triggering of Seismicity. Beginning with the earthquakes triggered by waste fluid injection at the Rocky Mountain Arsenal (20), it has been recognized that subsurface fluid injection is capable of triggering felt (of sufficient magnitude to be felt by nearby populations, so typically ML > 2) seismic events on preexisting tectonic faults (21). Recently, examples of tectonic activity trig- gered by disposal of waste water from hydraulic fracturing have been noted. Of course, it should be kept in mind that, of thou- Monitoring Geomechanical Deformation Fig. 1 also illustrates the variety of methods that can be used to monitor geomechanical deformation in the field. Although the importance of geomechanical deformation in oil production is becoming increasingly appreciated, monitoring it in the field remains something of a niche activity. Nevertheless, a number of SATELLITE GEODESY SEISMIC MONITORING MICROSEISMIC MONITORING BOREHOLE TILTMETERS BEDDING PARALLEL SLIP SURFACE UPLIFT WELLBORE FAILURE FAULT REACTIVATION SEAL FRACTURING INFLATION OF RESERVOIR Verdon et al., 2013 • Generally small magnitude, M<0, • Iden@fy poten@al leakage pathways, • Near real-‐@me analysis to provide early-‐warning, • Understand geomechanical response & verify models, • Aid seismic hazard assessment.
- 3. Major CCS projects 1. Weyburn, Saskatchewan • >30 Mt since 2000 • Constraining geomechanical models with microseismic observa@ons 2. In Salah, Algeria • ~4 Mt 2004-‐2011 • Changes in fracture characteris@cs during injec@on 3. Aquistore – Boundary Dam, SK • Began injec@on April 2015 • Using ambient noise to determine seismic veloci@es 3 2 November 2015 Image PTRC
- 4. 4 Weyburn passive seismic monitoring 2003 – 2011 200m 250m Injection: 2000 – present 1430m
- 5. Weyburn microseismic event locations Injection well 5 Magnitudes -3<Mw<-1 Producing wells Verdon et al., PNAS, 2013 Geophone array During injection After shut-in
- 6. 6 2 November 2015 % change in fracture poten@al Reservoir Overburden Injec@on well Producing well Modelling stress changes To match observed seismicity pa_ern an updated geomechanical model in required with a so`er reservoir. Verdon et al., EPSL, 2011
- 7. Weyburn - Summary • Microseismic observa@ons can provide important constraint on geomechanical models. • Model with a so`er reservoir than expected from core samples • Increases fracture poten@al in overburden above producing wells; • Decreases fracture poten@al in overburden above injec@on wells. • Seismicity caused by stress transfer, not fluid migra@on. 7 2 November 2015
- 8. 8 2 November 2015 In Salah passive seismic monitoring 2009 – 2011 Injection 2004 – 2011 Stork et al., IJGGC, 2015
- 9. 9 2 November 2015 In Salah, Algeria Stork et al., IJGGC, 2015
- 10. 10 2 November 2015 Fracture zone detected at injection depth (2km) Rutqvist, 2012 In Salah – Geophysical observations Ground movement detected by satellites (InSAR) Rucci et al., 2013
- 11. 2 November 2015 11 In Salah – Passive seismic observations >9000 events Mw=1.7 Stork et al., 2015
- 12. 12 2 November 2015 In Salah – Event locations Fig. 9. Event depths and horizontal distances from the observation well for dif- ferent tsp times, estimated using E3D. The colours represent the inclination of the P-arrival measured from the synthetic waveforms. The caprock and reservoir layers are shaded as in Fig. 2 and the approximate injection interval is between the two thicker black lines at ∼1.9 km deep. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Fig. 10. Estimated depth and horizontal distance of events from observation well. 0 0.5 1 1.5 2 −2.5 −2 Horizontal Distance (km) Fig. 11. Raytracing results for P- (red) and S-waves (gree times as a function of distance (upper panel), estimated usi 1-D velocity model and a source at 2.4 km deep (star). (F references to color in this figure legend, the reader is refer this article.) To provide additional evidence for the app obtained through finite-difference modelling tracing exercise. The results from ray-tracing th 1-D velocity model using the method of Ken (1989) show that events with hypocentres a 1.2 km horizontal distance from the array (Fig. To estimate errors in our reported locations of the velocity model on the travel-times an locate Cluster 2 up to 450 m shallower if the ve slower overall, if the near surface layer is 20% sl is anisotropic (see Stork et al., 2015 for a detaile would place the events in this cluster between deep and therefore extending up to 150 m unto As an estimate of the error in horizontal dista we take the maximum horizontal distance bet Fig. 9, this is 174 m when tsp = 0.60s near 0◦ inc tions obtained using the two methods, finite d and ray-tracing, agree within the estimated err Overall, the results for the estimated locatio that the seismicity occurred at depths over a ra below the injection interval and at azimuths fr well consistent with the activation of a pre-ex zone at the injection depth and extending into Stork et al., 2015 • Constant depth events • No evidence of migra@on to surface. Injection interval Geophone
- 13. 13 27 May 2015 Fracture characterisation from shear-wave splitting Concern: Is injection creating new fractures, allowing CO2 migration? Delaytimebetween splitwaves Stork et al., IJGGC, 2015 Dominant fracture orientation in direction of σH Delay time increases after high injection Returns to original value
- 14. In Salah - Summary • Proof-‐of-‐concept • Limited array but provides useful results • No evidence of shallower seismicity with @me • No evidence of shallow migra@on of CO2 • CO2 injec@on opens fractures that close when pressure decreases • Limits poten@al of CO2 leakage 14 2 November 2015
- 15. 15 2 November 2015 Aquistore passive seismic monitoring 2012 – 2015 2.5km x 2.5km array 50 – 64 1C/3C geophones 6m/20m deep 3 broadband stations Injection: Since April 2015 miles km 1 2 Inj Obs 1km
- 16. 16 2 November 2015 BOUNDARY DAM - AQUISTORE CO2 INJECTION PROJECT World’s first commercial power plant CCS project Image PTRC
- 17. 17 2 November 2015 BOUNDARY DAM - AQUISTORE CO2 INJECTION PROJECT Ben Rostron et al. / Energy Procedia 63 (2014) 2977 – 2984 Rostron et al., 2014
- 18. 18 2 November 2015 miles 2 1km Ambient seismic noise interferometry
- 19. Ambient seismic noise interferometry • Use noise recorded at receivers to produce velocity map • Cross-‐correlate noise at pairs of receivers (Bensen et al., 2007) • Create virtual source at one receiver 19 2 November 2015
- 20. Ambient Noise Tomography • Cross-‐correlate noise at pairs of receivers 20 2 November 2015
- 21. 49.10 256.95256.90 0.24 0.33 Velocity km/s Preliminary Tomography Results 21 2 November 2015 Depth sensitivity for periods 0.6 – 1.0sRayleigh wave group velocity 0.7s period Depth Fast Marching Surface Wave Tomography (Rawlinson et al., 2008)
- 22. Preliminary Tomography Results 22 2 November 2015 Depth 49.10 256.95256.90 0.24 0.33 Velocity km/s Rayleigh wave group velocity 0.7s period
- 23. Aquistore – Summary • Excellent baseline • Background seismicity • Near-‐surface characterisa@on • Allows @me-‐lapse studies • On-‐going array detec@on and loca@on studies • Broadband vs near-‐surface geophones vs downhole geophones vs fibre op@c • Similar geology to Weyburn – similar response? 23 2 November 2015
- 24. • Large CCS sites exhibit differing microseismic responses. • Weyburn 100s seismic events up to MW = -‐1.0 • In Salah 1000s seismic events up to Mw~ 1.7 • Aquistore? • Baseline data is crucial to • Highlight any ac@ve structures; • Evaluate effect of injec@on. • In Salah – ac@ve fracture zone iden@fied if earlier installa@on. • Use passive seismic monitoring to • Calibrate geomechanical models; • Determine fracture characteris@cs; • Observe changes in seismicity, velocity, fracture characteris@cs. • Conduct careful array design appropriate for purpose. 24 2 November 2015 Conclusions
- 25. 25 We thank the In Salah JIP, BP, Statoil and Sonatrach, for providing the microseismic data recorded at the In Salah site & for their permission to present this work. We thank the PTRC for providing permission to work with and present the Weyburn and Aquistore microseismic data. The author would like to acknowledge the financial support of the UK CCS Research Centre (www.ukccsrc.ac.uk) in carrying out this work. The UKCCSRC is funded by the EPSRC as part of the RCUK Energy Programme.
- 26. 26 BRISTOL UNIVERSITY MICROSEISMICITY PROJECTS BUMPS We thank the sponsors of the Bristol University Microseismicity Projects (BUMPS) consortium for supporting this research.