The Upper Devonian Duvernay Formation of Alberta: An Integrated Geochemical and Petrophysical Study in a Sedimentological and Stratigraphic Context

Abstract

The Upper Devonian Duvernay Formation is a significant unconventional exploration target in Alberta, particularly for liquids. We focus on the origin of heterogeneities in the Duvernay that are significant to the producibility of hydrocarbons. Sea level exerts a first order control on the sedimentology and stratigraphy of the Duvernay, which in turn are linked to mudstone composition and development of organic porosity. Establishing relationships between sea level cycles and shale porosity and permeability is an important part of our research. We report here on results and interpretations from long cores in five wells across the maturity gradient, including high resolution geochemical and petrophysical datasets. Interpretations are compared to a parallel sedimentological and stratigraphic analysis, providing an unusual opportunity for independent corroboration of models. Basinal facies are generally carbonate-poor mudstones, massive to finely laminated and typically enriched in pyrite. Shallower water facies are more carbonate-rich, often bioturbated, and contain a higher abundance of silt-sized shell debris. TOC decreases in carbonate-rich intervals but is unrelated to the clay content. Geochemical redox proxies indicate that deposition of TOC-rich intervals was associated with more reducing conditions. SiO2 varies inversely with carbonate content. We interpret a biogenic source for the silica. Shale composition exerts control over porosity and pore size distribution and the potential of the pore system to store and deliver gas. Data will be presented describing the relationships between geochemistry and pore system characteristics. Ion milled SEM photographs were analyzed for a range of TOC values. Types and abundance of porosity varied with TOC content. The lowest TOC sample had low porosity and was dominated by porosity hosted between mineral grains. The highest TOC sample had high porosity and was dominated by organic matter hosted porosity. A sample with intermediate TOC had a mix of porosity types. Organic matter content is highest in TST and HST deposits and increased biogenic silica creates brittle, non-fissile strata. By integrating geochemical properties and petrophysical parameters within the context of sea level, our goal is to improve the ability to identify and predict favourable locations where all factors affecting production are optimized.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015