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Sequence stratigraphic analysis of the Duvernay Formation, Kaybob area, Alberta, Canada

  • Author / Creator
    Shaw, Daniel
  • The Upper Devonian Duvernay Formation is an important hydrocarbon source rock in the Western Canada Sedimentary Basin and has been a significant unconventional oil, gas liquids, and gas reservoir since 2011. Heterogeneity in this and other shale reservoirs is important in predicting rock properties (such as TOC, porosity, permeability, and brittleness) within self-sourced reservoirs to identify target intervals. These properties can change with systems tracts and position within a basin at several scales and can be predicted by sequence stratigraphic models. In this study, we characterize the lithofacies of the Duvernay Formation and develop a sequence stratigraphic model for the formation in the Kaybob Area of Alberta. We also identify a set of features characteristic of mudstone sequence boundaries, describe how they vary stratigraphically and geographically, and interpret processes responsible for their formation.

    Five lithofacies were identified in 11 Duvernay cores from the Kaybob area of Alberta, characterized by composition, grain size, sedimentary structures, bioturbation, and cement. Lithofacies were deposited by a combination of suspension settling, sediment-gravity flows, and bottom currents under anoxic to fully oxygenated bottom water conditions. Lithofacies distribution was strongly affected by proximity to sediment sources, bottom topography, and sea level cyclicity. Relatively coarse-grained, carbonate-rich, bioturbated, and organic-poor facies are common close to large carbonate platforms and reefs; silt- and sand-rich facies deposited by bottom currents and sediment gravity flows are common on the slopes of large carbonate platforms; hemipelagic deposited, fine grained, biosiliceous, organic-rich facies are common in distal areas of the basin. Transgressive deposits are characterized by increasingly fine-grained, biosiliceous, organic-rich facies; highstand deposits by increasingly coarsegrained, carbonate-rich, bioturbated, organic-poor facies; lowstand deposits by detrital clay-rich, bioturbated facies.

    Sequence stratigraphic surfaces were identified in the 11 cores and correlated across a network
    of approximately 600 wireline wells in the Kaybob area to develop a sequence stratigraphic model. Three 3rd order depositional sequences and 4th order depositional sequences are identified within the Duvernay. Two types of 3rd order sequence boundaries are identified, their expression dependent on their position within a 2nd order depositional sequence that encompassed the Duvernay. In the 2nd order transgression, sequence boundaries are expressed as scoured surfaces with coarse overlying lags that represent a period of sediment starvation and reworking during lowstand conditions and early transgression. In the 2nd order highstand, sequence boundaries are expressed as soft sedimentdeformed surfaces overlain by coarse beds that represent a period of forced regression, with the sequence boundary located at the top. Surfaces become gradational and overlying lags or forced regressive deposits thin basinward.

    The high-density data set in our relatively small study area enables us to map 3rd and 4th order sequence stratigraphic surfaces across the study area with a high degree of certainty. We were also able to interpret major sources of sediment and determine geographic extent of topographical features during different stages of Duvernay Formation deposition from geographic distribution of facies and variations in systems tract isopachs. Our interpretation of sequence boundaries produced during a 2nd order TST are consistent with several previous studies that interpreted sequence boundaries in mudstones as combined sequence boundaries and transgressive surfaces overlain by winnowed lags. Our interpretation of sequence boundaries produced during a 2nd order HST differs from previous studies in that we propose the coarse sand beds at sequence boundaries were deposited during forced regression, with the sequence boundary located at its top.

  • Subjects / Keywords
  • Graduation date
    Spring 2021
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-ztg7-7h84
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.