Induced Seismic Monitoring: Insights from a Duvernay Case Study

Transcription

1 Induced Seismic Monitoring: Insights from a Duvernay Case Study Dario Baturan*, Emrah Yenier, Ray Morin, David Damico Presented at CSUR Induced Seismicity Workshop December

2 Introduction Significant increase in seismicity near Crooked Lake, Alberta (~30 km west of Fox Creek) observed starting in late 2013 Local and regional networks deployed to monitor seismicity over the past 2 years Case study involving a 4-station seismic network commissioned by Repsol Address some of the key aspects of induced seismic monitoring (ISM): Seismic network performance Review different monitoring strategies vs public network performance Event magnitudes Understanding differences in reported magnitudes Instrumentation Effect of instrument selection on seismic data products and regulations Risk management Seismic data as a potential real-time indicator of the likelihood of the occurrence of large events 2

3 Seismic Networks 1. Public seismic network CRANE, RAVEN, TransAlta 4 permanent real-time streaming stations within 200 km of the study area Nearest station ~ 65 km away 2. Near-regional seismic array ~12 semi-permanent stations located 5 to 110 km from the center of the block Operational since July 2015 as a subscriber array Shallow-buried seismometers 3. Local seismic array 4 seismic stations within the block 2 stations shared with the regional seismic array Deployed and continuously operational since December 2014 Sensors installed in 15 screw piles Study area 3

4 Seismic Network Performance AGS Catalog Regional Array Catalog Local Array Catalog 244 recorded events Jan 2015 to Nov 2016 Magnitude of completeness (Mc) ~ 2.3 B-value ~ 0.9 Diffuse cloud of events 472 recorded events Jul 2015 to Nov 2016 Magnitude of completeness (Mc) ~ ML1.1 B-value ~ 0.8 Seismicity starting to delineate 2-4 distinct clusters 2516 recorded events Dec 2014 to Nov 2016 Magnitude of completeness (Mc) ~ ML0.6 B-value ~0.9 Seismicity distributed among ~12 different clusters 4

5 Local Seismic Array Catalog A B A B Public network Mc Regional network Mc Local network Mc Magnitude distribution of high SNR events Regional and local arrays Mc well below AER req Public networkdetected seismicity tip of the iceberg 5 distinct event clusters activated at different times Cluster(s) 1 seismicity associated with HF operations on the Repsol wells Clusters 2-5 associated with HF operations on neighbouring wells Good spatial and temporal correlation to HF operations Residual seismicity associated with the fault adjacent to the southern B well ongoing months after the well has been shut in 5

6 Event Location Comparison Local vs regional catalog Local vs AGS catalog Relative relocation of events further delineates faults trending NE-SW 184 events common to both catalogs Regional array locations have more scatter Event epicenters shifted by 0 to 6.8 km Average shift 1.5 km with standard deviation 1 km 62 events common to both catalogs Public network locations have the most scatter Event epicenters shifted by 0 to 11.2 km Average shift 2.7 km with standard deviation 2.4 km 6

7 Magnitude Comparison Comparison of ML magnitudes computed by different networks indicates that on average M L (local array) < M L (AGS) :27:23 M4 Earthquake Average difference 0.2 magnitude units Standard ML models over-correct ground motions for distance attenuation at distances of Less than 30 km More than 100 km Calibrated equation removes distance (or most of recording network) dependence 7

8 Magnitude Comparison Comparison of two most widely used magnitude scales to describe size of an earthquake: Richter (Local) Magnitude Scale (ML) Referenced by AER Moment Magnitude (Mw) Referenced by BC OGC Study area: ML (WCSB calibrated) and Mw attain similar values for events of M>3 ML is smaller than Mw for M<3 Similar trends were observed in other regions B-values computed from Mw magnitudes will be higher (~0.3) than b-values from ML magnitudes 8

9 :27:23 M4 Earthquake BB seismometers with 2.6 cm/s clip level (0.1 to 10 Hz) Single instrument clipped 2.2 km epicentral distance Single horizontal channel Seismometer clip level Magnitudes M L 4.8 (H&B equation) Mw 4.1 (RMT solution)

10 Instrumentation Closest instrument clipped due to Proximity to the source Site amplification effects Proximity to the nodal plane Cannot use clipped instrument for GM or M estimates, however P and S picks still valid Accurate magnitude and ground motions still computed by the rest of the array Other 3 recorded the event on scale 4.4 to 8.8 km epicentral distance Accelerometer would not clip on this event BC OGC regulations specify an accelerometer for this reason Higher clip level comes at a cost of higher self noise Accelerometer DR common Seismometer DR

11 ISM as Risk Management 2 3 1B What type of data can be used in real-time to manage risk? Seismicity rate, b-value, cumulative seismic moment, probability of occurrence, completions parameters (pressure, volume etc.) Some common seismicity traits for the study region b-values consistently below 1 before large events Most large events occur following the initial spike in seismicity rate 3 11

12 ISM as Risk Management Unique conditions at each pad/well Higher monitoring resolution key to real-time risk management Mc well below M1.0 Accurate data products Delineate faults through increased location accuracy and larger catalog Combine data with completions parameters Real-time mitigation focus of ongoing research using rich data sets recorded to date 12

13 Summary Key takeaways from the study area seismic catalog evaluation: Seismicity has close temporal and spatial relation to HF operations Local arrays required for good depth constraint Public network event locations can be off by up to 10 km Uncalibrated equations result in magnitude discrepancies between local, regional and public networks Mw and ML magnitude scale do not have a 1:1 relationship for smaller events Use accelerometers if the only desired outcome is on-scale near field recording Use seismometers to get a richer data set Higher resolution provided by local networks potentially a key to risk management Utilize rich data sets recorded to dateto understand the triggering mechanisms and recognize signs of high risk fault activation implement in real-time monitoring systems 13

14 Acknowledgement: Seismographic data from the 4 stations the study area was provided by Repsol Canada Thank You Dario Baturan Director, Technical Operations dariobaturan@nanometrics.ca