Understanding the relationship between shale gas potential and depositional environment in the Duvernay Formation, Kaybob area, Canada: Implications for lithofacies identification of shale gas reservoir

초록

The lithofacies of hydrocarbon-bearing stratigraphy possess distinct physical and chemical properties that are directly related to their hydrocarbon generation potential and brittleness. Systematically studying the lithofacies and their depositional environments therefore facilitates a more accurate evaluation of shale gas reservoir characteristics. In this study, an attempt was made to identify suitable lithofacies for efficient shale gas extraction through a comprehensive evaluation of the hydrocarbon generation capacity and brittleness index (BI) and reveal their depositional conditions of the Duvernay Formation in the Kaybob area. The hydrocarbon generation potential was inferred from the original generative organic carbon (GOCo) content, and the BI was calculated based on the mineral composition. Based on the sedimentary characteristics, the Duvernay mudstones were classified into four lithofacies: white laminated mudstone, Mlw; crudely stratified mudstone, Mc; laminated mudstone, Ml; and papery fractured mudstone, Mpf. Mlw has a high GOCo content and BI, indicating that it can generate significant volumes of hydrocarbons and form a clean fracture under stress. Based on geochemical proxies, variations in shale gas potential according to lithofacies were found to be related to the interplay of primary productivity in the surface water (excess-SiO2 and P2O5), clastic sediment input (Al2O3, TiO2, and Hf), and redox conditions in the bottom water (Th/U, EFU, and EFMo). The Mlw, with excellent shale gas potential, was deposited in association with enhanced primary productivity within surface water, diminished clastic sediment input, and reducing conditions in the bottom water, which led to an enrichment of organic matter and biogenic silica in the mudstones. The Upper Duvernay Formation, mainly composed of Mlw with a minor amount of Mc, is considered a primary target for shale gas exploration.

키워드