Design of monitoring networks

Seismic monitoring is used for different purposes. Whether it is for the national seismic network or monitoring of seismic activity around dams, tailing facilities, or nuclear power plants, designing the appropriate network helps with getting the anticipated results.

Event identification

Reliable magnitude and hypocenter determination is the ultimate goal of seismic networks. Depending on the density of the seismographic stations, identified events helps with delineation of geological structures such as faults or determination of the extend of fracture networks and production areas, therefore, playing an important role in the future of costly operations involving fluid injection. Also, current traffic light protocols in western Canada require continuous reporting of any seismic event with magnitude 2 and higher and the shut down of operations if a magnitude 4 is reached.

Seismicity studies and seismic hazard assessment

Earthquakes associated with various oil and gas activities such as waste-water disposal and hydraulic fracturing have become a topic of focus in the central eastern US and western Canada. Events as large as M5.6 have occurred due to the long-term injection of fluid into geological layers, triggering pre-existing critically stressed faults. Assessment of seismic hazard from potentially damaging earthquakes prior to the initiation of injection projects helps mitigating the seismic risks to the oil and gas facilities and public structures. Probabilistic seismic hazard assessment is a critical tool in understanding the likelihood of exceeding specific levels of ground motion in a time window, usually the life span of the structures in question. Currently seismic hazard models from natural earthquakes are routinely provided for the national building codes. With increasing number of injection operations across US and western Canada, these models need to be revisited to capture the true picture of seismic hazard in north America. Typical seismicity studies for injection operations include:

  • Baseline studies for background seismicity prior to start of operations.
  • Design of seismic monitoring network suitable for identification of earthquakes with magnitudes as low as 2 according to the requirements of Alberta Energy Regulator’s subsurface order No. 2 and BC Oil and Gas commission.
  • Event identification and ground motion analysis.
  • Fault activation analysis during operations and after flowback to include the delay in the response of the affected area to injection.
  • Seismic hazard maps for different ground motion levels.

Subbottom Acoustic Profiling (SAP)

SAP is a technique that can be used to create 2D images of the sediments beneath a water body. Applications of this technique include explorations in shallow waters, search for underwater pipelines and cables, imaging the water column and gas seepage monitoring, and identification of disturbance in the sediment column as a result of ground motion from the past earthquakes.