Correlation, Mapping and Interpretation of Geochemically Distinct Intervals Within the Duvernay Formation

Abstract

The development of carbonate mudrock and shale reservoirs worldwide has highlighted small-scale mineralogical and stratigraphic complexity in fine-grained rocks that were once thought to be fairly uniform. Resolution of these complexities can be aided through geochemical analyses and correlation of distinct elemental pairings and ratios. Geochemical variations represent changes to the paleophysiochemical conditions during deposition and changes in the mineralogy due to input from different sources. In this study, detailed chemostratigraphic correlation of the Duvernay Formation was undertaken in some key areas of development of this resource in Alberta (e.g. Kaybob field). Samples were collected for geochemical analyses that were performed using ICP-MS, ICP-OES, and handheld XRF. Correlation of element and oxide data along with elemental ratios was achieved by using Pearson product-moment correlation coefficient and eigenvectors to highlight relationships and define geochemically similar packages. These packages were mapped by integrating chemostratigraphic picks with well logs, allowing for the creation of several isopach maps of geochemically distinct units. Early findings revealed bimodal populations of silica. These populations have been recognized in the Duvernay Formation as relating to 1) detrital weathering products (e.g. K2O, TiO2, Zr) and 2) elevated phosphorous, possibly linked to a time of slowed deposition and increased pelagic fallout. Rare earth element profiles were normalized to the Post Archean Australian Shale and used as a proxy for oxygen levels during deposition. The flattened nature of these profiles and elevated middle rare earth patterns imply intervals of suboxia and anoxia; some normal marine profiles were also noted near the base of the Duvernay Formation, where normal oxygen levels are inferred. Understanding the relationships of these distinct packages to each other and to sediment transport regimes present at the time of deposition will aid in further exploration of the Duvernay Formation in Alberta and other similar shale gas plays around the world.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016