Spatiotemporal changes in seismic velocity associated with hydraulic
fracturing-induced earthquakes near Fox Creek, Alberta, Canada
Abstract
To characterize the subsurface geomechanical response to hydraulic
fracturing activities, we study the spatiotemporal changes of seismic
velocity during the completion of four injection wells in the Fox Creek
area, Alberta, Canada. We estimate temporal velocity changes (dv/v) from
ambient seismic noise recorded during the Tony Creek Dual Microseismic
Experiment (ToC2ME) by comparing a 5-day stacked noise correlation
function with a reference noise correlation function stacked over the
deployment period. In the frequency band (0.1 - 0.4 Hz) most sensitive
to the injection depths (~3.4 km), we observe daily dv/v
that revealed alternating gradual velocity decreases and increases with
magnitudes in the range of ±0.9%. We found a strong temporal
correlation between the onset of velocity decreases and periods of
intense seismicity, suggesting that the observed dv/v reductions are
likely caused by stress-induced subsurface deformation due to elevated
pore pressures, increased crack density, and ground shaking. A period of
dv/v increase observed between the beginning and end of different well
stimulation is attributed to crustal healing. Comparing the dv/v time
series with injection parameters, we observed a 272.66% increase in
induced seismicity and 50% more reduction in dv/v during the second
injection phase that are correlated with 90.53%, 169.64%, and 4.34%
increase in the injection volume, rate, and pressure, respectively. Our
study provides valuable new information on the changes in reservoir
elastic properties within the Western Canadian Sedimentary Basin. It
also demonstrates that coda wave interferometry using data from dense
seismic arrays near injection sites can be an additional tool for
monitoring hydraulic fracturing operations.