The BC Oil and Gas Commission has identified two causes of induced
seismicity related to oil and gas activities – wastewater disposal and hydraulic fracturing. Both activities introduce pressure under the earth’s surface, which may trigger a seismic event. None of the events that have taken place in B.C. have resulted in any property damage or hazards to safety or the environment.
Wastewater disposal is the deep underground disposal of water that has been used for oil and gas activities. Disposal wells are used to sequester oil and gas field waste by-products in deep underground formations. This fluid is predominantly saline water associated with oil and gas production or flow-back from hydraulic fracture operations.
The Commission provides in depth regulatory oversight of disposal wells to ensure wellbore and formation integrity, safe operation and the containment of disposal fluids. Disposal formations include depleted oil or gas pools, or a formation already containing highly saline water. Formation pressure increases due to disposal, in certain situations, can cause existing deep faults to slip, thereby creating a seismic event. Mitigation of induced seismicity related to wastewater disposal can be accomplished by limiting injection rates to control formation pressure or ceasing disposal.
Hydraulic fracturing is the process of injecting water into underground natural gas bearing formations at high enough pressures to create fractures in the rock or shale, which opens fractures and allows natural gas to flow. This energy can trigger movement along pre-existing stressed faults, leading to an induced seismic event.
Nearly all occurrences of induced seismicity in B.C. related to the oil and gas industry are not felt at the surface. Events generally occur at depths greater than 1.5 kilometres below the surface and are of a low magnitude. Residents that reported seismic events to the Commission said they were like “something hit the side of the house” or “someone slammed the front door.” Felt events are usually of a short duration, typically a single jolt, and in all reported cases less than a few seconds of shaking.
The risk of damage or injury from induced seismicity is very low. Less than 0.2 per cent of hydraulic fracturing operations cause felt events. The intensity of felt events has been moderate and the associated vibrations are not expected to be great enough to cause damage. There have been no reports of injury or major structural damage related to seismic events in northeast B.C. The Commission undertook two full studies on induced seismicity in 2012 and 2014 which include detailed data on seismic events. More information is available under What’s Being Done?