Browsing by Author "Eaton, David William S."

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    Analysis and modelling of induced seismicity in fluid-driven settings and on laboratory faults
    (2024-05) Khajehdehi, Omid; Davidsen, Jörn; Eaton, David William S.
    Seismicity, whether natural from tectonic plate motion, induced by industrial activities, or observed on laboratory faults, is complex due to nonlinearities and long-range spatiotemporal correlations in the Earth's crust. Previous studies revealed spatiotemporal clustering and aftershocks, reminiscent of tectonic earthquakes, in fluid-induced seismicity and seismicity on laboratory faults. Fluid-induced seismicity arises from industrial activities like hydraulic fracturing (e.g., a 4.6Mw in Alberta, Canada) and enhanced geothermal systems (e.g., a 5.5Mw in Pohang, South Korea), where high-pressure fluids are injected into the Earth's crust to improve hydrocarbon extraction or geothermal reservoir permeability. This seismicity raises concerns for industry, regulators, and residents, highlighting the challenge of identifying underlying processes and estimating fluid-induced seismic hazards. Further, ongoing debate persists on the presence or absence of magnitude clustering in seismicity, with implications for improved short-term earthquake magnitude forecasting. Therefore, to address these challenges, we investigate the underlying causes of field observations from a modelling perspective and utilize laboratory stick-slip experiments to enhance our understanding of seismicity. We introduce a novel model of fluid-induced seismicity combining viscoelasticity with fluid diffusion and invasion percolation to simulate crustal rheology and stress interactions in porous media. This model accurately elucidates the spatial footprint of fluid-induced seismicity and reproduces aftershocks akin to tectonic loading. Moreover, at high injection rates, recovering aftershock statistical properties requires direct access to the internal stress dynamic, potentially explaining the absence of reported aftershock triggering in some studies (e.g., Soultz geothermal sites, France). In a reported case of significant aftershock triggering in the Kiskatinaw area, BC, Canada, we find that smaller magnitude, more frequent triggers primarily drive this triggering, consistent with past instances in fluid-induced settings. Additionally, we observe localized spatiotemporal clustering, characterized by a rapid spatial decay in aftershocks beyond the rupture length, suggesting the dominant influence of fluid migration in this region. Finally, our analysis of seismicity on laboratory faults contributes to the debate over magnitude clustering in seismicity. Our study reveals magnitude clustering occurring exclusively during slip events on laboratory faults, resulting from variations in frequency-magnitude distributions. This thesis offers valuable insights into complex seismicity dynamics and enhances efforts in (fluid-induced) seismic hazard assessments.
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    Characterization of the southern Rocky Mountain Trench near Valemount, British Columbia, using receiver functions
    (2020-05-21) Coffey, Juliann Rose; Gilbert, Hersh; Eaton, David William S.; Dettmer, Jan
    The Rocky Mountain Trench (RMT) within the eastern Canadian Cordillera marks a prominent topographic and physiographic boundary within the exotic terrains that accreted onto the North American continent. Previous geophysical data have shown that the RMT coincides with a ∼10 - 15 km decrease in crustal and lithospheric thickness from east to west. Receiver function (RF) analysis is a suitable method for investigating the RMT because it provides estimates of the depths of lithospheric boundaries. A deployment of ten broadband seismometers between July 2017 and July 2019 within the RMT near Valemount, B. C., recorded over 300 teleseismic earthquakes with magnitudes greater than 5.5 at epicentral distances between 30◦ and 100◦ degrees. Due to high levels of cultural noise in the region, removing low signal-to-noise ratio events left between 57 and 17 events per station to use for further analysis. Assuming average crustal velocities, stacks of low frequency RFs show a high-amplitude positive arrival at depths greater than 45 km. When viewed at higher frequencies, these RFs reveal arrivals at depths between 20-30 km. These RFs are analyzed through joint inversions with a surface wave dispersion curve, common conversion point stacking, and H-k stacking. There are three major findings of this study: (1) The Moho near the RMT around Valemount is relatively deep (> 45 km) and the crust is thicker to the south, interpreted to indicate that this location marks the northern most segment of the portion of the southwestern Canadian Cordillera where the crust underwent a greater amount of shortening and thickening compared to the rest of the Cordillera. (2) Strong midcrustal discontinuities are present in the RF stacks, and they are interpreted to mark the depth of the Rocky Mountain basal detachment, corresponding to the interface between the North American basement and accreted terranes. (3) The RF signals vary strongly with back-azimuth, likely resulting from a combination of crustal heterogeneity, anisotropy, and dipping layers.
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    Modelling Hydraulic Fracturing in Tight Reservoirs Using Equivalent Continuum Approach
    (2021-01-29) Atdayev, Eziz; Wong, Ron Chik Kwong; Eaton, David William S.; Davidsen, Jörn; Duncan, Neil A.
    Hydraulic fracturing has transitioned into widespread use over the last few decades. There are a variety of numerical methods available to simulate hydraulic fracturing. However, most current methods require a large number of input parameters, of which the values of some parameters are poorly constrained. This research proposes a new method of modelling the hydraulically fractured region using void-ratio and strain dependent relation to define the permeability of the fractured region. This approach is computationally efficient and reduces the number of input parameters. By implementing this method with an equivalent continuum representation, uncertainties are reduced arising from heterogeneity and anisotropy of the earth materials. The computational efficiency improves modelling performance in stress-sensitive zones such as in the vicinity of the injection well or near faults.
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    New technologies for unconventional reservoir characterization: Seismic inversion, focal-time estimation, and signal processing to improve reservoir imaging
    (2020-05-04) Weir, Ronald McKenzie; Lawton, Don Caleb; Pedersen, Per Kent; Eaton, David William S.; Schmitt, Douglas R.; Oetelaar, Gerald
    Seismic data, comprising both passively and actively recorded data, have long been used for resource evaluation and geohazard assessments. Unconventional resource extraction, such as Alberta’s Duvernay play, requires a multifaceted approach to optimize reservoir development and to mitigate geohazards such as induced seismicity. Frequently, hydraulic fracture stimulation programs do not go as planned; fractures occur out of zone, depart from the predicted models, and, in some cases, induce felt seismic events (induced by hydraulic fracturing operations). From the Fox Creek, Alberta study area are well log data, multicomponent seismic reflection data, and microseismic data recorded from a permanent near-surface passive recording array. For this study, an industry partner provided two multicomponent seismic reflection surveys, as well as two co-located passive microseismic surveys. The Microseismic Industry Consortium (MIC) supplied microseismic data from the Tony Creek dual microseismic experiment (ToC2ME); an anonymous industry contributor contributed a second passive survey. Technologies developed in this thesis enable more accurate positioning of microseismic hypocenters by incorporating seismic reflection data. Signal-processing techniques used in seismic reflection processing are employed in this thesis to enhance the detection quality and quality of induced seismic events. Structural interpretation provides a framework of vital information to map and understand the relationship between geological structure and induced seismic events. Constraints obtained from full-waveform inversion provide detailed information about the properties of the Duvernay Formation itself, such as brittle and ductile facies. Accurate microseismic hypocenter determination in the context of seismic analysis identifies which structural elements and reservoir facies control the direction and size of induced fractures and which faults may be responsible for induced seismicity. Hypocenters are accurately located and plotted in depth and are associated with faults mapped from the reflected seismic. This analysis highlights what geological conditions, faults, lithology, and structure are dominant factors with respect to hydraulic fracture propagation and induced seismicity. The results of this research will aid in the design of hydraulic fracture completion programs and geohazard (induced seismic event) mitigation.
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    Seismicity and tectonic interpretation of the Southern Rocky Mountain Trench near Valemount, British Columbia, Canada
    (2020-05-15) Purba, Joshua Chris Shadday; Dettmer, Jan; Gilbert, Hersh; Eaton, David William S.; Trad, Daniel O.
    The Rocky Mountain Trench is a large geological feature in the Canadian Cordillera with complex structures. Although efforts to understand the structure of the trench have been conducted through refraction-seismic, reflection-seismic, and geological studies, detailed knowledge of the trench is still sparse but crucial to understanding its evolution. Here, I conduct a local seismic study that involves earthquake detection, arrival-time picking, earthquake location, and a tectonic interpretation of the Rocky Mountain Trench in the area of Valemount, British Columbia. I developed and employed a nonlinear, probabilistic multiple-earthquake location for earthquakes detected here. The location provides both earthquake locations and rigorous estimates of their uncertainties. Based on analysing one year of data, my catalogue includes 47 local earthquakes that I identified and located. The results of the multiple-earthquake location presented here illustrates uncertainty reduction in depth from 18 to 5 km compared to the depths of earthquakes calculated based on single-earthquake locations. This lower depth uncertainty permits better inferences of the tectonic development of the Rocky Mountain Trench. The earthquake locations determined here displays a change in the distribution of seismicity around Valemount. Seismicity extends to the west of the RMT and the south of Valemount. While to the north, the seismicity is primarily confined to the trench and areas to the east. The distribution of seismicity also supports the dome-shaped Malton Gneiss in the subsurface. Seismic velocities are consistent with metamorphic rocks and the presence of significant amount of quartz in crustal rocks.
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    Towards real-time microseismic processing: Efficient and robust methods for event detection and automated arrival time picking
    (2020-06-11) da Silva Paes, Atila; Eaton, David William S.; Dettmer, Jan; Trad, Daniel O.; Lawton, Don Caleb; do Nascimento, Aderson Farias
    Hydraulic fracturing (HF) is a method to enhance the production of crude oil and natural gas trapped in impermeable geologic formations. HF technology has the capability to unleash reserves that were previously considered uneconomical. Microseismic (MS) monitoring involves the detection and localization of microseismic events, including induced seismicity generated by HF. MS methods are used to aid in HF design optimization. A typical MS survey may last months and generates terabytes of raw data, motivating the use of automatic triggering and location algorithms. To address these challenges, workflows are developed in this thesis based on novel methods for event-detection, event-validation and arrival-time picking. These workflows are applicable for a variety of acquisition geometries and signal-to-noise ratio, as well as real-time applications and post-acquisition processing modes. The Tony Creek Dual Microseismic Experiment (ToC2ME), a MS program acquired in west-central Alberta by the University of Calgary within the Duvernay unconventional play, was used as case study. A detailed study of signal quality and noise was undertaken, leading to substantial improvement in processing results. The noise analysis showed that approximately half of the stations are strongly influenced by cultural noise, making their use counterproductive in detection algorithms but generally suitable for automatic arrival-time picking of the data from the station. A new algorithm developed for event-detection, called energy stack, provides a similar detection rate to previous method, but has advantages of having significantly faster execution speed, fewer parameters and the ability to detect events that were previously undetected. A new method for arrival-time picking uses the kurtosis derivative, a high-order statistical measure, in a sliding window. This approach yields accurate and precise arrival time picks under diverse noise conditions. In summary, when compared to other methods that are currently used, the developed workflows are robust in different noise environments, advantageous for implementation since they use fewer parameters, are computationally faster and require less human interaction. All of these constitute desirable features for real-time microseismic monitoring systems.
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    Understanding Canadian Cordillera crustal and upper-mantle structure with joint Bayesian inversion of receiver functions and surface-wave dispersion curves
    (2020-08-20) Smale, Jacquelyn; Dettmer, Jan; Gilbert, Hersh; Eaton, David William S.; Lauer, Rachel M.
    The accretion of exotic terranes onto the stable Northern American craton during the formation of the Northern Canadian Cordillera (NCC) generated complex structure on a crustal and lithospheric scale. Without making significant model-parametrization assumptions, inverting for structure is challenging. The Bayesian approach quantifies uncertainty due to non-uniqueness of the solution and can avoid subjective choice in model parameterization. Jointly inverting receiver-functions and surface-wave dispersion curves constrains shear-wave velocity structure. With this inversion method, I study the spatial variability of major lithospheric discontinuities, specifically of the Mohoroviciˇ c discontinuity (Moho) and lithosphere-asthenosphere boundary (LAB), along a transect from Whitehorse to Toad River. Results show a flat Moho across the NCC at ∼ 34-km depth and a heterogeneous LAB with depths between 70- and 100-km depth. Beneath the LAB, I observe a significant low-velocity zone with shear-wave velocities as low as ∼ 3.0 km/s. Only the presence of partial melting of 1.5–2.5% can explain these Vs reductions.