Hide and Seek: Identification and Analysis of Operational Micro-Seismicity Below the Noise Level During a Hydraulic Stimulation Experiment

Date: 4/26/2019

Time: 09:30 AM

Room: Cascade I

The Tony Creek Dual Microseismic Experiment (ToC2ME) dataset provides a unique opportunity to investigate operational micro- and induced-seismicity in relation to a hydraulic fracturing experiment in western Alberta. Previous work by researchers at the University of Calgary has identified ~25,000 microseismic events within this dataset and located up to ~18,500 of these using a combination of a stacked amplitude-envelope methodology, template matching using 15 master events, and beam-forming techniques. However, most of the events identified are not thought to be directly associated with the operational fracturing procedure. In this case, operational microseismicity is believed to occur below the noise level leading to an incomplete catalog of detections.

Here, we use an STA/LTA algorithm and coincident trigger methodology to identify microseismicity across a network of 68 geophones. Our thresholds for detection are set reasonably low in order to detect as many events as possible, whilst minimising false alarms. We find many events with clear phase arrivals which have not been identified in previous catalogs of this dataset, but that are locatable. The amplitudes, inter-event times and frequency contents of the waveforms identified are investigated for temporal and spatial changes, indicative of changing conditions at depth. Furthermore, we use the events identified by the STA/LTA algorithm in a template matching procedure to further populate the catalog with low amplitude events that may be hidden by noise or temporal spacing. Our results suggest that a number of families of repeating seismicity occurred during this experiment, and subtle changes in parameters relating to these families, including the similarity of events within the family as identified by a cross correlation co-efficient, can reflect small but important changes in the subsurface. A thorough understanding of these changes relating to the updated catalog of microseismicity is important, in particular in relation to hazard analysis for hydraulic fracturing experiments.

Presenting Author: Rebecca O. Salvage

Authors