How is modern hydraulic fracturing a little bit like having a baby? For the answer to this and other questions about earthquakes, seismicity, and safe natural gas extraction, read on.
By The Resource Works Society, 2016
1. How is modern hydraulic fracturing a little bit like having a baby?
When a mom-to-be goes in for an ultrasound scan, sound at an ultrasonic frequency is employed to create a picture of the fetus. Modern hydraulic fracturing employs the same concept of sound waves to see what is not visible to the naked eye.
For the geologists applying cutting-edge science to the process of extracting natural gas, they too have the problem that the topic of interest is out of sight. With fracking processes, the gas-bearing rock layer is buried deep underground, often in the range of 5 km.
Sonic monitoring allows technical experts on the surface to “see” where they are drilling. Thanks to sonar signals, they can spot problem areas and take measures to avoid them.
During the few weeks when a gas well is undergoing fracturing, these experts are able to monitor the vibrations triggered by precise fracking actions.
2. Seismicity has been proven to be associated with fracking. Should we be concerned?
Seismicity is a recorded earthquake caused primarily by fault movement, typically referring to events greater than a 0.5 magnitude.
Induced seismicity is an event resulting from human activity, and can be caused by industries such as mining and natural gas development.
Induced seismicity is seldom felt at the surface and in British Columbia events have been recorded at low magnitudes.
3. What rules are in place governing seismicity?
-
Formal reporting requirements
-
Require monitoring when fracking near disposal wells
-
Required enhanced monitoring in high-risk areas, disposal wells, ‘felt' areas
-
Report magnitude 2.0 events and suspend operations at magnitude 4.0
4. What has government done about the issue of seismicity in natural gas extraction?
There is now a lot more information available, particularly since 2012. Measures taken by the BC Oil and Gas Commission include:
Recommendations from the 2012 and 2014 reports called for enhanced seismicity monitoring, including an increase in the number of seismic monitoring stations.
Recommendations were implemented after each study. This has led to more accurate data.
Measuring Earthquakes: The commission uses the Richter magnitude scale in reporting seismic events, which can occur as both positive and negative numbers.
Specific updates include:
- Nine new seismograph stations were installed in the Canadian National Seismograph Network in northeast BC, greatly increasing the ability to monitor for seismicity in the region.
- In addition, 13 localized seismograph arrays have been installed by operators to provide more detailed seismological data.
- New regulations were implemented that require the immediate suspension of hydraulic fracturing if a magnitude 4.0 or greater event is triggered, as well as the mandatory reporting of felt events.
- Operations can only be resumed with the implementation of a commission-approved mitigation plan.
- The requirement for risk assessments of disposal wells, which operate under strict volume and pressure restrictions. Implementation of buffer zones, prohibiting hydraulic fracturing operations around the Peace and Bennett Dams.
- Scientific studies with the University of British Columbia to further understand induced seismicity.
5. What is the Monitor, Stop, Study rule?
This is what many in the natural gas industry call the procedures now in place to manage seismicity:
-
Monitor: use dense monitor arrays so there is abundant information. Use this information to avoid known problem faults and share information with authorities. For all events starting at magnitude 2.0, report the information.
-
Stop: If seismic activity of 4.0 is reached, work must stop.
-
Study: Describe known incidents and mitigation options with the regulators, make plans for moving forward.
6. How big a risk is seismicity?
-
Earthquakes have been associated with conventional oil and gas withdrawal (that is the kind that does not require hydraulic fracturing).
-
The process of hydraulic fracturing a well as presently implemented for shale gas (or unconventional) recovery does not pose a high risk for inducing "felt" seismic events.
-
Monitoring has shown that the vast majority of fracturing operations generate low intensities, well below 1.0 on the Richter scale. A handful of instances of higher levels of seismic activity have been documented (out of hundreds of thousands of wells fractured over the past 50 years).
-
Seismicity in fracking is always associated with a nearby active fault.
-
Virtually all oil and gas operations conduct 3D seismic monitoring prior to planning the wells.
-
Faults can be, and ought to be, identified and avoided.
7. How do fracking operators manage the risk of seismicity?
Modern 3D seismic imaging can identify the location and lengths of all but the smallest faults. Small faults are not a concern as a source of damaging earthquakes. So the remedy in large part lies in performing these surveys before a fracturing or wastewater disposal operation. Other procedures that give control over seismicity risk:
-
pump rates
-
bypassing stages
-
exit re-activation zone
-
flowback
-
know where the risk is elevated.
8. Is this a brand new problem we are just hearing about for the first time?
No. Regulators in British Columbia have been studying seismicity for years.
The 2012 Observed Seismicity in the Horn River and the 2014 Observed Seismicity in the Montney Trend reports concluded seismic activity in areas of the Horn River Basin (between 2009 and 2011) and the Montney Trend (2013 to 2014) were triggered by injection during hydraulic fracturing. All seismic events were low magnitude.
The 2014 Montney report showed 231 seismic events within the Montney Trend were recorded by Natural Resources Canada during the Aug. 2013 to Oct. 2014 study period. The report concluded 93 of these events were triggered by hydraulic fracturing, or 2.6 per cent of the 7,400 hydraulic fracturing stages. Only about 0.15 per cent of these events were felt at surface.
9. Is hydraulic fracturing the only kind of human activity that can trigger seismicity?
Induced seismic activity has been described since at least the 1920s and attributed to various human activities including the impoundment of water reservoirs, controlled explosions related to mining and construction, underground nuclear tests, and energy technology developments that involve injection or withdrawal of fluids from the subsurface. Historically known induced seismicity has generally been small in both magnitude and intensity of ground shaking.
This is not about whether one kind of energy (natural gas) is better or worse than another. If one was to say, "Let’s stop all human practices that could cause seismicity," you’d also be looking at stopping:
- Hydro dams
- Geothermal
- Mining
- Building roads
10. What are the key learnings?
-
Earthquakes are generated when there is Earth movement in a fault.
-
A fault is a fracture in the Earth with significant displacement of the rock on either side of the fracture. To cause movement, the human activity would need to pour energy into what is known as an active fault. This is a fault which, when energized, will cause Earth movement.
-
Faults can be detected. Modern 3D seismic imaging can identify the location and lengths of all but the smallest faults. Small faults are not a concern as a source of damaging earthquakes. So the remedy in large part lies in performing these sur- veys before a fracturing or wastewater disposal operation.
- Constantly improving and evolving practices mean seismicity is understood and managed.
THIS FACT SHEET ON FRACKING, SEISMICITY, AND OTHER TOP CONCERNS FOR BRITISH COLUMBIA’S NATURAL GAS INDUSTRY WAS PREPARED USING AUTHENTICATED SOURCES FROM ACADEMIA AND GOVERNMENT REGULATORS.