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TitleWell-log-based velocity and density models for the Montney unconventional resource play in northeast British Columbia, Canada, applicable to induced seismicity monitoring and research
AuthorBabaie Mahani, A; Malyskyy, D; Visser, R; Hayes, M; Gaucher, M; Kao, HORCID logo
SourceSeismological Research Letters 2020 p. 886-894,
Alt SeriesNatural Resources Canada, Contribution Series 20200422
PublisherSeismological Society of America
Mediapaper; on-line; digital
File formatpdf; html
ProvinceBritish Columbia
AreaDawson Creek; Fort St. John
Lat/Long WENS-123.2500 -120.0000 57.7500 54.7500
Subjectsfossil fuels; geophysics; Economics and Industry; Nature and Environment; Science and Technology; Health and Safety; energy resources; petroleum industry; petroleum resources; hydrocarbons; hydrocarbon recovery; hydraulic fracturing; earthquake risk; seismicity; geophysical logging; well logging; density logging; models; seismic interpretations; seismic waves; seismic velocities; Montney Play; Kiskatinaw Seismic Monitoring and Mitigation Area; North Peace Ground Motion Monitoring Area; monitoring
Illustrationslocation maps; well logs; profiles; models; geoscientific sketch maps; histograms
ProgramEnvironmental Geoscience Shale Gas - induced seismicity
Released2020 11 25
AbstractWe present detailed velocity and density models for the Montney unconventional resource play in northeast British Columbia, Canada. The new models are specifically essential for robust hypocenter determination in the areas undergoing multistage hydraulic-fracturing operations and for detailed analysis of induced seismicity processes in the region. For the upper 4 km of the sedimentary structure, we review hundreds of well logs and select sonic and density logs from 19 locations to build the representative models. For depths below 4 km, we extend our models using data from the southern Alberta refraction experiment (Clowes et al., 2002). We provide one set of models for the entire Montney play along with two separated sets for the southern and northern areas. Specifically, the models for the southern and northern Montney play are based on logs located in and around the Kiskatinaw Seismic Monitoring and Mitigation Area and the North Peace Ground Motion Monitoring area, respectively. To demonstrate the usefulness of our detailed velocity model, we compare the hypocenter location of earthquakes that occurred within the Montney play as determined with our model and the simple two-layered model (CN01) routinely used by Natural Resources Canada. Locations obtained by our velocity model cluster more tightly with the majority of events having root mean square residual of <0.2 s compared with that of <0.4 s when the CN01 model is used. Cross sections of seismicity versus depth across the area also show significant improvements in the determination of focal depths. Our model results in a reasonable median focal depth of ~2 km for events in this area, which is consistent with the completion depths of hydraulic-fracturing operations. In comparison, most solutions determined with the CN01 model have fixed focal depths (0 km) due to the lack of depth resolution.
Summary(Plain Language Summary, not published)
An accurate velocity model is required to determine the precise epicenter and focal depth of an earthquake. This is particularly important for the Montney area of northeastern BC where most local seismicity are related to hydraulic fracturing injections, and therefore precise determination of earthquake locations has significant implications for both regulators and operators. In this study, we review hundreds of well logs and select sonic and density logs from 19 locations to build the most accurate models specifically for precisely locating earthquakes in the Montney area. When compared to the routine earthquake catalogue determined with an oversimplified two-layered model used in routine location process, our solutions show tight clusters of events in the vicinity of injection wells with smaller time residuals between the predicted and observed arrival times. Our models also provide better depth resolution so that fixing the focal depth during the location process is no longer necessary.

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