How did hydraulic-fracturing operations in the Horn River Basin change seismicity patterns in northeastern British Columbia, Canada?

Abstract

An increase in regional seismicity has been documented for the Horn River Basin (HRB) since the development of shale gas began in late 2006. Operational parameters of all hydraulic-fracturing (HF) treatments in the HRB between November 2006 and December 2011 were compiled from completion reports collected by the British Columbia Oil and Gas Commission (BCOGC). This database was compared with regional earthquake catalogs to delineate a quantitative relationship between the observed variation of regional seismicity and local HF operations. Taking the HRB as a whole, results suggest that the total injected volume from hydraulic fracturing is a more significant factor in affecting the pattern of local seismicity than injection pressure is. However, no clear change in background seismicity can be observed when the total monthly injected volume is less than ∼ 20,000 m3. The initial effect of increasing injected volume is an increase in earthquake frequency but not magnitude. Relatively large seismic- moment release (> 1014 N m) occurred only when the monthly injected volume exceeded ∼ 150,000 m3. Variable time lags, from days to four months, are observed between intense HF and the occurrence of a significant local earthquake. The hydrologic properties of the source formations and local geologic conditions (such as distribution, geometry, and dimension of preexisting faults) also might play important roles in induced seismogenesis, in addition to the total volume of injection.