Waveform Similarity of Micro-seismicity at the ToC2ME Hydraulic Fracturing Experiment Site
Abstract
This thesis quantitatively investigates the waveform similarity of micro-earthquakes detected during the Tony Creek Dual Microseismic Experiment (ToC2ME) located in Fox Creek, Alberta. Subsurface anthropogenic activities, especially processes involving injection, can lead to accumulation of porepressure and elastic strain in the geologic formations and rocks, resulting in induced earthquakes. Four hydraulic-fracturing treatment wells were drilled and completed in the study area. The microseismic acquisition system monitored continuous seismic waveforms from 25 October to 15 December 2016 revealing 21619 hydraulic fracture-related events with magnitude ranging from Mw -1 to 3.2. The present study compares and discusses similarity of waveforms captured by 69 stations using two waveform similarity clustering algorithms: 1) Clusty and 2) PageRank, to form clusters of earthquakes with similar waveform content. The performance of this clustering is validated by visual inspection of these waveforms and their spatial and temporal distribution. These clusters are analyzed in terms of their b values, nearest neighbour statistics, and corresponding spanning trees. A porepressure model is also developed to understand the spatial and temporal distribution of porepressure throughout the injection process. This model was then used to identify the mechanisms of different clusters as it relates to the hydraulic fracturing program.
These analysis suggest earthquakes at the site can be attributed to two main sources. Clusters in lower zone #1, zone #7, and zone #5 are likely induced by the activation of pre-existing faults, while clusters in zone #2 and #4 tend to relate to fractures directly induced by the hydraulic fracturing process. Waveforms relating to hydraulic fractures tend to exhibit shorter P-wave packets compared to the activation of natural fractures. These results could be applied at hydraulic fracturing sites such as unconventional oil&gas or geothermal energy extraction to gain insight into the size and shape of the stimulated reservoir.