Low-Frequency Tremor Signals from a Hydraulic Fracture Treatment in Northeast British Columbia, Canada

The Rolla Microseismic Experiment (RME) was undertaken by the Microseismic Industry Consortium August 7-28, 2011 to record a multistage hydraulic fracture stimulation of a Triassic unconventional gas reservoir in northeastern British Columbia, Canada. The microseismic deployment included a 6-level downhole toolstring with low-frequency (4.5 Hz) geophones, a set of 21 portable broadband seismograph systems, and a 12-channel surface array comprised of 10-Hz geophones. Although we did not observe LPLD events based on how they have been previously described, our data exhibit high-amplitude signals in the 8-15 Hz band. These signals are monotonic and have been interpreted as resonance of fluid-filled cracks or successions of small repetitive events. We have also detected several instances of discrete microseismic events with unusually low frequency. An apparent tendency for low-frequency tremors to precede high-frequency microseismicity in our data provides a tantalizing suggestion that these processes may be genetically linked.