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The Zen Path to the Kingdom of Kerogen: A Case Study of the Duvernay Shale

Brad Stirrett

The organic-rich Duvernay Fm was deposited within an intracratonic basin in upper Devonian time and covers a large portion of the Western Canadian Sedimentary Basin. Regionally, the organic rich Duvernay is high in silica, low in clay, has variable carbonate content with minor pyrite, and compares favorably to other unconventional shale reservoirs across North America. The porosity in the Duvernay Shale owes its origins entirely to the conversion of kerogen, thus understanding the drivers behind regional maturity and heat flow trends is critical for deciphering both reservoir quality and hydrocarbon richness. Across the mapped 100,000 sq. km fairway Devonian reefs grew along emergent paleohighs, basement structures, and regional lineaments. Reefal geometries reflect basin scale tectonic features and govern the distribution of autochthonous material, mineralogy, sedimentary structures, and the stratigraphy of the Duvernay Shale.

The role that basement scale tectonics played in the evolution of the reefs and the associated shale basin is profound and provides the context by which regional maturity morphologies, fracture and fault patterns, and associated pressure cells have been measured, mapped, and predicted. Integrated geochemical data from all publicly available and proprietary data has been modelled and utilized to build maturity maps that have predicted the distribution of liquid yields and fluid densities to date. It has been observed that there is a strong correlation between maturity, pressure, reservoir quality, and shale thickness to the syndepositional tectonic settings and an integrated model is here presented to explain the context of how these parameters all coincide to create one of the most exciting liquid rich shale fairways in North America.

The Duvernay Shale sweet spots are defined as: net shale greater than 30m; internal carbonate thickness less than 5m; liquid yields between 50 and 500 Bbls/MMcf; pressure gradients greater than 15.8 kPa/m; and the presence of good ductile seals in the overlying Ireton and underlying Majeau Lake formations. By utilizing all of the classic tools of research and basin analysis combined with modern technologies including tight rock analysis, geochemistry, FIB-SEM imaging, advanced fluid analysis, pressured coring, modern log analysis, and a little imagination and creativity; this presentation will show how Encana was able to identify and capture more than half of the high graded fairway in the Duvernay shale.

AAPG Search and Discovery Article #90186 © AAPG Geoscience Technology Workshop, Hydrocarbon Charge Considerations in Liquid-Rich Unconventional Petroleum Systems, November 5, 2013, Vancouver, BC, Canada