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TitleFrom seismic quiescence to surged activity after decades of wastewater disposal: a case study in central-west Alberta, Canada
AuthorYu, HORCID logo; Kao, HORCID logo; Visser, R; Wang, B
SourceGeophysical Research Letters vol. 48, issue 22, e2021GL095074, 2021 p. 1-11,
Alt SeriesNatural Resources Canada, Contribution Series 20210340
PublisherAmerican Geophysical Union
Mediapaper; digital; on-line
File formatpdf; html
NTS83L/07; 83L/08; 83L/09; 83L/10
AreaSmoky River
Lat/Long WENS-119.0000 -118.0000 54.6667 54.3333
Subjectsgeophysics; stratigraphy; Science and Technology; Nature and Environment; Economics and Industry; Health and Safety; earthquakes; earthquake risk; earthquake magnitudes; seismicity; seismic risk; liquid waste disposal; waste disposal wells; groundwater regimes; stress analyses; fluid migration; bedrock geology; lithology; sedimentary rocks; reefs; structural features; faults; seismological network; stratigraphic nomenclature; hydrostratigraphic units; Western Canada Sedimentary Basin; Duvernay Formation; Swan Hills Formation; Musreau Lake Sequence; Woodbend Aquitard; Waste water; Phanerozoic; Paleozoic; Devonian
Illustrationslocation maps; geoscientific sketch maps; time series; stratigraphic charts; plots; schematic models
ProgramEnvironmental Geoscience Shale Gas - induced seismicity
Released2021 10 28
AbstractInjection-induced earthquakes associated with wastewater disposal (WD) in the Western Canadian Sedimentary Basin are much fewer than those linked to hydraulic fracturing. Recently, 43 WD-related earthquakes (M1.3-3.9) occurred in a historically seismically quiet area where long-term injections became intensive since 2018, foreshadowing a critical stress state accumulated from long-term injections. Our improved earthquake locations show that the injection well targeting the deeper middle-upper Devonian aquifer system causes more vigorous seismicity with a wide range of stress drop values (0.8-230 MPa) compared to other shallower wells. Three physical mechanisms may collectively lead to the observed seismic pattern: (a) the underlying Devonian reef system makes it easier for injected fluids to migrate horizontally, (b) fluids can be channeled into the widespread critical faults and migrate vertically to cause earthquakes along it, and (c) aseismic slip probably triggered within the Duvernay formation by fluid migrating can further facilitate seismicity at shallower depths.
Summary(Plain Language Summary, not published)
Earthquakes can be triggered during fluid injections. In the Western Canadian Sedimentary Basin, the operation of wastewater disposal appears to have caused much fewer earthquakes than hydraulic fracturing. Recently, a sequence of 43 small-to-moderate-sized earthquakes occurred in a seismically quiet area, where injections have been safely operated for more than two decades prior to becoming intensive in 2018. The refined earthquake distribution confirms that these earthquakes are related to disposal injections. Among the four active wells, the one with a deeper injection depth caused more earthquakes than other shallower wells. As the injection of the deeper well is close to the ancient reef system, horizontal fluid migration is facilitated and more likely to reach nearby faults. Fluid migration along sub-vertical faults can cause deeper earthquakes in the basement and aseismic creep in the overlying shale formation. The induced aseismic slip can further load the adjacent fault segment and foster earthquakes at shallow depths.

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