Despite being a relatively well-understood world-class hydrocarbons source rock, mudstones of the Duvernay Formation have regained recent research interest because of their vast potential as an unconventional resource play. The Late Devonian (Frasnian) Duvernay Fm. is among the few reservoirs in the world recording basinal organic-rich mudstones contemporaneous to adjacent reef buildups. Detailed sedimentological and stratigraphic analysis of well cores and outcrops were conducted in this study to characterize the intrinsic small- and large-scale heterogeneity caused by lateral and vertical facies changes. Using outcrops of the Perdrix Fm. (equivalent Duvernay strata) and subsurface well cores, this thesis focuses on investigating the role of carbonate reef margins on facies heterogeneity and expression on reservoir properties important for fluid storage and production. Based on interpretations of hydrodynamic, biogenic, and diagenetic processes, the sedimentary facies analysis suggest that reefs not only supplied abundant carbonate detritus, but also might have controlled the extent of the bottom-water anoxia, the sediment transport pathways, and diagenetic reactions within basinal deposits. Further, facies associations and stacking patterns suggest a sedimentary system controlled by allogenic forces, such as fluctuations of the relative sea-level. The sedimentary facies and stratigraphic analysis were combined with petrophysical properties to understand the nature and vertical distribution of mudstone microfabrics across reservoir areas of the East Shale Basin. The variety of identified mudstone microfabrics and associated pore networks provides the basis for predicting reservoir qualities according to interpretations of sedimentary processes, not only in the Duvernay Fm. but also for analogue mudstone reservoirs where organic-rich mudstones accumulated under the influence of an adjacent reef buildup.