Sequence Stratigraphic Analysis Of The Duvernay Formation Shale, Kaybob Area, Alberta — CSUR Technical Webinar, March 9
The Upper Devonian Duvernay Formation mudstone is an important hydrocarbon source rock in the Western Canada Sedimentary Basin and has been a significant unconventional reservoir since 2011. Understanding heterogeneity within self-sourced reservoirs is important in predicting rock properties (such as TOC, porosity, permeability, and brittleness), which may be used to identify target intervals. These properties change with systems tracts and position within a basin at several scales and may be predicted by sequence stratigraphic models. Our analysis of 11 long cores in the Kaybob area identifies five lithofacies deposited by a combination of suspension settling, sediment-gravity flows, and bottom currents under anoxic to fully oxygenated bottom water conditions. Three 3rd order depositional sequences (DS1-3) are identified within the Duvernay Formation, bounded by 4 sequence boundaries (SB0-3). Sequences are defined by vertical facies patterns in cores and by stratal stacking patterns on wireline logs.
The bases of DS1 and DS2 are major flooding surfaces that mark the beginning of transgressive systems tracts (TST) and are characterized by increasingly fine-grained, organic-rich, biosiliceous facies. The TSTs are overlain by highstand systems tracts (HST), represented by increasingly coarse-grained, carbonate-rich, bioturbated, organic-poor facies. The base of DS3 is marked by a rapid transition to detrital clay-rich, bioturbated facies, interpreted to be a lowstand systems tract (LST), which is overlain by a TST and HST. These three 3rd order cycles are superimposed on a 2nd order late TST and early HST, in which the 2nd order MFS coincides with the MFS in DS2. Fourth order depositional sequences (2-8 m scale) are also identified in the Duvernay, based on trends within depositional packages that include increasing calcite content, decreasing TOC, increasing abundance and size of burrows, and increasing grain size.
Two types of 3rd order sequence boundaries are identified, their expression dependent on whether they occur within the 2nd order transgression or highstand. 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 sediment-deformed 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.
PRESENTERS: Daniel J. Shaw, University of Alberta.
Location: Zoom Webinar
Date/Time Information: Tuesday, March 09, 2021 (from 10h00 to 11h00) – Mountain Time
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