Browsing by Author "Schultz, Ryan"

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    Faults and associated karst collapse suggest conduits for fluid flow that influence hydraulic fracturing-induced seismicity
    (2018) Galloway, Elwyn; Hauck, Tyler E.; Corlett, Hilary; Pena, Dinu; Schultz, Ryan
    During December 2011, a swarm of moderate-magnitude earthquakes was induced by hydraulic fracturing (HF) near Cardston, Alberta. Despite seismological associations linking these two processes, the hydrological and tectonic mechanisms involved remain unclear. In this study, we interpret a 3D reflection-seismic survey to delve into the geological factors related to these earthquakes. First, we document a basement-rooted fault on which the earthquake rupture occurred that extends above the targeted reservoir. Second, at the reservoir’s stratigraphic level, anomalous subcircular features are recognized along the fault and are interpreted as resulting from fault-associated karst processes. These observations have implications for HF-induced seismicity, as they suggest hydraulic communication over a large (vertical) distance, reconciling the discrepancy between the culprit well trajectory and earthquake hypocenters. We speculate on how these newly identified geological factors could drive the sporadic appearance of induced seismicity and thus be utilized to avoid earthquake hazards.
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    Linking fossil reefs with earthquakes: geologic insight to where induced seismicity occurs in Alberta
    (2016) Schultz, Ryan; Corlett, Hilary; Haug, Kristine; Kocon, Ken; MacCormack, Kelsey; Stern, Virginia; Shipman, Todd
    Recently, a significant increase in North American, midcontinent earthquakes has been associated with contemporaneous development of petroleum resources. Despite the proliferation of drilling throughout sedimentary basins worldwide, earthquakes are only induced at a small fraction of wells. In this study, we focus on cases of induced seismicity where high-resolution data are available in the central Western Canada Sedimentary Basin. Our regional comparison of induced earthquake depths suggests basement-controlled tectonics. Complementary to these findings, hypocenters of induced seismicity clusters coincide with the margins of Devonian carbonate reefs. We interpret this spatial correspondence as the result of geographically biased activation potential, possibly as a consequence of reef nucleation preference to paleobathymetric highs associated with Precambrian basement tectonics. This finding demonstrates the importance of geologic/tectonic factors to earthquake induction, in addition to industrial operational parameters. In fact, the observation of induced seismicity silhouetting deep fossil reef systems may be a useful tool to identify future regions with increased seismogenic potential.
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    Subsurface faults inferred from reflection seismic, earthquakes, and sedimentological relationships: Implications for induced seismicity in Alberta, Canada
    (2018) Corlett, Hilary; Schultz, Ryan; Branscombe, Paulina; Hauck, Tyler E.; Haug, Kristine; MacCormack, Kelsey; Shipman, Todd
    Given the recent induced seismic activity in Alberta, identification of subsurface faults and areas of structural complexity has become increasingly important in improving our understanding of the controls on induced seismic events. Using a 3D geological model supplemented with 2D and 3D reflection seismic data, several basement-bounded and basement-rooted faults, which extend upward and into the Devonian strata, are identified in areas coincident with increased seismic activity. The presence of faults in the study area was confirmed through a statistically significant correlation of high-quality seismic event data from historical and recent (1970–2016) induced earthquakes in Alberta to the edge of the Devonian-aged Swan Hills platform. Along with the identification of faults using reflection seismic and earthquake hypocenter data, a review of the role of pre-existing structure on depositional patterns that has been previously used to infer deep structure in this area, is also presented in this study. Several pre-existing extensional and/or transtensional style faults in the deeper strata and shallow basement of the study area are consistent with structure influencing the sedimentation of the overlying stratigraphy. Therefore, a better understanding of genetic fault-reef associations and the relationship to overlying strata may aid in identification of fault locations, style, and orientation. Considering the advancement of proper avoidance strategies during the planning stages of unconventional resource development or storage, this paper demonstrates the use of geological knowledge and relationships to identify areas comprising faults that may be prone to reactivation.