Induced seismicity refers to earthquakes caused or significantly influenced by human activity rather than natural tectonic processes. These events can range from imperceptible micro-earthquakes to events that damage property, affect public safety, and disrupt industry operations.
Activities Associated with Induced Seismicity
Induced seismicity results from altering the state of stress in a pre-existing “critically stressed” subsurface fault, often through changes in pore pressure or fault loading conditions. In Alberta, the following industrial activities could potentially induce seismicity:
- Fluid disposal: A common and significant cause of induced seismicity, particularly during oil and gas production. Large volumes of saline water (a by-product of oil and gas extraction or spent hydraulic fracturing fluid) are injected into underground formations through disposal wells. In some instances, the increased pore pressure from the injected fluid alters the stress conditions of the pre-existing critically stressed faults, allowing them to slip and trigger earthquakes.
- Hydraulic fracturing (fracking): This process involves injecting high-pressure fluids to fracture reservoir rocks to enhance oil and gas extraction. Although hydraulic fracturing produces microseismic events, it has been linked to fault reactivation and earthquakes.
- Underground gas or carbon dioxide (CO2) storage: Injecting gas or CO2 for storage purposes can affect subsurface stress and potentially trigger seismic events.
- Geothermal energy production: Geothermal schemes produce high volumes of saline water from which heat is extracted. The cooled fluids are typically reinjected into the same unit or a nearby deep reservoir to maintain pressure and support long-term energy production. The injection process can affect subsurface stress and potentially trigger seismic events.
- Brine-hosted mineral production: Brine-hosted mineral extraction schemes produce high volumes of saline water from which minerals are extracted. The spent fluids are then disposed of in deep reservoirs. The production and injection processes can affect subsurface stress and potentially trigger seismic events.
- Mining operations: Surface and underground mining can cause induced seismicity due to load changes on the surrounding rock as material is extracted.
- Dam impoundment: Large dam reservoirs change subsurface stresses due to the weight and pressure of the impounded water. These stress changes could lead to induced seismicity.
Regulations Covering Injection Activities in Alberta
Subsurface fluid injection activities may involve hydraulic fracturing, fluid disposal, enhanced oil recovery, geothermal energy production, brine-hosted mineral extraction, and carbon sequestration activities. In Alberta, these resource development activities are regulated under specified enactments and energy resource enactments.
Our Requirements for Induced Seismicity
Induced seismicity requirements for subsurface injection activities are outlined in the following AER subsurface orders and directives.
| Regulatory instrument | Zone or extent | Description |
|---|---|---|
| Subsurface Order No. 2A | Duvernay (Central Alberta) | Induced seismicity requirements for hydraulic fracturing operations for zones from and including the Duvernay Formation to the basement within a specified area. Includes monitoring and response for earthquake magnitude thresholds defined for the subsurface order area. |
| Subsurface Order No. 6 | Duvernay (Brazeau) | Induced seismicity requirements for hydraulic fracturing operations for zones from and including the Duvernay Formation to the basement within a specified zone. Includes monitoring and response for earthquake magnitude thresholds defined for the subsurface order area. Setbacks for critical infrastructure are specified, and no hydraulic fracturing operations may occur in certain zones within the area outlined. |
| Subsurface Order No. 7 | Duvernay (Red Deer) | Induced seismicity requirements for hydraulic fracturing operations for zones from and including the Duvernay Formation to the basement within a specified zone. Includes monitoring and response for earthquake magnitude thresholds defined for the subsurface order area. Setbacks for critical infrastructure are specified. |
| Directive 065: Resources Applications for Oil and Gas Reservoirs | Provincial | Subsurface requirements for fluid disposal schemes, including requirements for seismic hazard and risk assessments and a monitoring, mitigation, and response (MMR) plan |
| Directive 089: Geothermal Resource Development | Provincial | Requirements for geothermal resource development below the base of groundwater protection. Includes induced seismicity requirements for geothermal wells and an MMR plan. |
| Directive 090: Brine-Hosted Mineral Resource Development | Provincial | Requirements for brine-hosted mineral resource development. Includes induced seismicity requirements for brine-hosted wells and an MMR plan. |
Regulatory tools addressing hydraulic fracturing in the Duvernay Formation
Compliance and Enforcement
We regularly conduct inspections and audits. With the aid of compliance tools, we ensure that companies are following our requirements and meeting approval conditions. If we find that a company is noncompliant, we will take the appropriate compliance and enforcement actions.
Monitoring, Mitigation, and Response Plan
The monitoring, mitigation, and response (MMR) plan outlines how the disposal scheme approval holder will mitigate the risk of induced seismicity for identified seismic hazards and the actions taken should a seismic event occur. Actions include communicating with identified stakeholders after a “red light” event when there is any essential infrastructure that falls within a ten-kilometre radius of the well in question.
Earthquakes and Induced Seismicity Monitoring and Reporting
Starting in 2013, the Alberta Geological Survey (AGS) installed a network of seismic stations in the province, mainly in areas of increased earthquake activity (see earthquakes and induced-seismicity). Regional seismic monitoring is publicly available and is a compliance backstop for reporting and identifying induced seismic events throughout the province. The AGS has created a series of annual seismic hazard maps that include natural and induced seismicity since 2011. These maps illustrate the likelihood of an area to reaching or exceeding a certain ground motion caused by an earthquake over a set period. Also, the AGS created the Alberta Earthquake Dashboard to provide information about earthquakes in Alberta.
