Feb 25, 2015 - Case Study: Fox Creek, Alberta. ⢠Key Points. Marathon ... Injection-Induced Earthquakes, William L. Ellsworth, Science. 12 July 2013, 341 no.
Seismic Hazards from
Induced Seismicity Western Science - Research Leaders Forum Wednesday, February 25, 2015
Outline • Seismic Hazard Analysis • Fracking and Induced Seismicity Case Study: Fox Creek, Alberta
• Key Points
Marathon Oil entered the Niobrara’s Denver/Julesburg basin in 2010. The emerging Niobrara is described as having tight, layered chalk and marlstone with some natural fracturing, where hydraulic fracturing methods can be applied. Pictured is an H&P FlexRig. Photo courtesy of Bruce Kelsch, Marathon Oil
Seismic Hazard Analysis: aims to predict expected shaking (target probability) so that facilities can be designed to withstand
3
M3.0 M2.0 M1.0
1 Magnitude M
Hazard curve
(Shaking vs distance relations)
Ground motion parameter
2
Ground motions
(Earthquake number, sizes, rates)
log # quake > M
(Earthquake locations)
How often?
Distance R
Probability of exceedance
Where?
Total
2 1 3 Ground motion parameter
Annual frequency of exceedance of a target ground-motion level at the site, considering all possible scenarios and their relative likelihood.
Seismic Hazard Analysis
Increasing Hazard
Example: Expected shaking (at a given vibration period) in National Building Code of Canada for 2% chance of exceedance in 50 years (design ground motions, considers historical earthquakes, continuation of historical pattern is implicit)
The Problem • Oil and gas boom enabled by new horizontal-drilling technologies • Accompanied in many places by a noticeable increase in seismicity
Graphic from Ellsworth, 2013 (Science, July 2013), showing rise in seismicity rates in the central United States. The red line shows the cumulative count of earthquakes of M>3 in the geographic region of the inset map. The dashed line corresponds to the long-term rate of 21.2 earthquakes per year.
Mechanisms for Inducing Earthquakes
Injection-Induced Earthquakes, William L. Ellsworth, Science 12 July 2013, 341 no. 6142, DOI: 10.1126/science.1225942
Induced earthquakes in Oklahoma – most believed due to wastewater injected at depth
; 0 fatalities; very few injuries
“Oklahoma is now the second most seismically active state in the continental U.S., after California.”
Lorca, Spain Earthquake • On 11 May 2011, a M5.1 earthquake struck southern Spain, killing nine people and seriously damaging buildings in the nearby town of Lorca. • The earthquake was surprisingly destructive, given its modest magnitude. • Known human-induced stress changes related to groundwater extraction probably triggered the Lorca earthquake and caused its shallow depth (González et al., Nature).
The Lorca Earthquake caused widespread damage, and destroyed the St. James church, pictured here. (Photo: Creative Commons)
Hydraulic Fracturing Hydraulic fracturing, or fracking, is the name of an unconventional process for extracting natural gas from underground shale beds. Injection massive quantities of sand and chemicals at high pressures, causing networks of fractures to open. Pressurized mixture breaks the shale bed The sand particles hold the cracks open to allow gas to flow out up the well, where it is harvested. http://www.thecoast.ca/halifax/what-we-know-we-dont-know-about-fracking/Content?oid=4384360
Wastewater Injection Water (brine) injection depths are usually deep, in rocks naturally stressed with faults capable of generating earthquakes.
Wastewater Injection Wells ......... greater zone of impact ......... deeper ......... longer duration
Wastewater well
Fracking well
1.21 barrels of total drilling waste are generated for every foot drilled in the United States. ~ American Petroleum Institute
Hydrofrac Zone deep injection may trigger earthquakes due to stress relief on faults adapted from geology.com
Hazards of Induced Earthquakes Estimating the hazard from induced seismicity is more difficult than for natural seismicity because of the small database of induced seismicity observations both in terms of seismic source characterization and ground-motion prediction. We are trying to quantify a potential new seismic source.
Case Study: Fox Creek, AB Evaluate the extent to which the potential for induced seismicity at a site alters the pre-existing hazard from natural seismicity.
It is in an area of previously low seismicity which suddenly became active in Dec. 2013. The presumed cause of the seismicity is hydraulic fracturing activity that initiated at that time, and is ongoing.
There are no disposal wells nearby; large-volume injection wells are not a potential cause for the induced seismicity. http://ar.atha.com/2012/reserves-resources/
Case Study: Fox Creek The likelihood of getting potentiallydamaging levels of ground shaking (as indicated by peak ground acceleration, PGA) could increase by 1 to 2 orders of magnitude. Damage threshold level ~100 cm/s2
Probability of initiating a significant sequence
Case Study: Fox Creek The expected ground motions that you would need to design for could increase by factors of two to ten. In low-to-moderate seismicity environments, the hazard from an induced-seismicity source, if one is activated in close proximity to a site, can greatly exceed the hazard from natural background seismicity.
Protocols that should be put in place to monitor induced seismicity during hydraulic fracturing
Seismic monitoring of hydraulic fracturing operations is essential, so that branching out of seismicity is detected early and correlated with the operation. A simple, conservatively tuned ‘traffic light system’ is advisable to interrupt operation if earthquakes start to be a concern (i.e., M0.5 observed? M1.0? M2.0?)
© Department of Energy & Climate Change
Bulletin 2015-07 February 19, 2015 Subsurface Order No. 2: Monitoring and Reporting of Seismicity in the Vicinity of Hydraulic Fracturing Operations in the Duvernay Zone, Fox Creek, Alberta
• During the drilling seasons of 2013/14 and 2014/15, the AER and AGS observed unexpected persistent patterns of seismic events above background levels west of the community of Fox Creek, Alberta. Based on the timing of these events, the AER and AGS believe that they may be associated with multistage hydraulic fracturing in the Duvernay Zone.
AER Traffic Light System – Duvernay Zone, Fox Creek 4.0 ML Cease operations, inform the AER 2.0 ML Inform the AER, invoke response plan 2.0 ML No action required
Induced seismicity from hydraulic fracturing … • The micro-earthquakes and aseismic slip creates the pathways for the gas/oil. • Fracking usually induces very small earthquakes (M = -1; the size of a dinner plate)
Maximum size of induced events not yet known… • Avoid large volume wastewater injections if possible (surface treatment). • Stay away from active or easily re-activated faults.
• Avoid operations near sensitive infrastructure.
• In rare cases, the progressing frac continues growing via tectonically loaded faults: Hydro-fracking Hydro-shearing • In this scenario, larger earthquakes are possible and have been observed (Maximum M so far ~4, Fox Creek; Fort St. John). 1966 Italian Spaghetti Western film directed by Sergio Leone, starring Clint Eastwood, Lee Van Cleef, and Eli Wallach
Stefan Wiemer, 2014
www.inducedseismicity.ca
“We know how to start earthquakes, but we are still far from being able to keep them under control”. Jean-Philippe Avouac, California Institute of Technology
