Induced seismicity associated with shale gas development

Abstract

The development of unconventional oil and gas in North America has caused a significant increase of seismicity in areas of intense injection operations, including both hydraulic fracturing and wastewater disposal. These induced earthquakes have attracted considerable media attention due to their potential seismic hazards. In 2012, NRCan initiated the Induced Seismicity Research (ISR) Activity as part of the Shale Gas Research Project, under the Environmental Geoscience Program, to investigate the possible relationship between hydraulic fracturing (HF) of shale gas and the changing pattern of local seismicity. In 2015, the activity was expanded to a Project to include studies of all injection-related seismic events. NRCan's ISR Project has three major tasks. The first is to improve real-time earthquake-monitoring capability in major shale gas basins where the station coverage of regional seismograph network is sparse. The second is to establish the baseline of regional seismic pattern (i.e., the pre-development reference line) for places where the development potential of unconventional oil and gas is deemed high in the foreseeable future. The third is to conduct targeted studies on significant induced events to understand the relationship between their seismogenesis and man-made operations. In collaborations with many partners, new real-time broadband seismograph stations have been installed in BC, AB, NB, QC, NT, and YT. Studies of local seismicity before, during, and after HF operations have been completed for the Horn River Basin (northeast BC), the Moncton and Sussex areas (southern NB), and the Norman Wells area of the central Mackenzie Valley (NT). An increase of local seismicity in BC and AB is spatially and temporarily correlated with the peak period of injection operations associated with shale gas development. Injection volume appears to play a more important role than injection pressure in causing induced events. No abnormal seismicity can be observed when the injection volume is small. The initial effect of increasing injected volume is an increase in earthquake frequency but not magnitude. Relatively large induced events occurred only when the monthly injected volume becomes very large. However, large injection volume seems to be a necessary condition for the occurrence of relatively large induced event, but not a sufficient one. Research results of the largest hydraulic fracturing-induced earthquake to date (the August 17, 2015, Mw 4.6, northern Montney earthquake) indicate that the peak ground acceleration can be as high as 17% g at an epicentral distance of 5 km, suggesting that seismic hazards due to induced seismicity is not negligible.