POROSITY CHARACTERIZATION AND PREDICTION IN THE MIDDLE TO LATE DEVONIAN HORN RIVER GROUP, CENTRAL MACKENZIE VALLEY, NORTHWEST TERRITORIES, CANADA

The Devonian Horn River Group is a thick, organic-rich mudstone and carbonate succession present in Northwestern Canada that comprises the Hare Indian, Ramparts, and Canol formations. As the source of the hydrocarbons produced from the Kee Scarp Reefs at Norman Wells, this unit is now considered as a shale reservoir prospect, with unconventional oil in place estimates of 145 BB in the Canol Formation and 46 BB in the Hare Indian Formation. Despite being a key factor to evaluate unconventional resource potential, the nature of porosity in the Horn River Group of the Central Mackenzie Valley, Northwest Territories has yet to be studied in detail. To achieve this goal, a combination of He porosimetry, N₂ adsorption experiments, and scanning electron microscope (SEM) imaging from the Husky Little Bear N-09 well southeast of Norman Wells, NWT, was used to characterize porosity. These results were compared to mineralogy from x-ray diffraction, facies and microfacies distributions, and thermal maturity proxies to elucidate the controls and predictors of porosity in the Horn River Group of the N-09 well. Helium porosimetry results show that porosity ranges from 3.2% to 13.1% while N₂ experiments suggest that the majority of mesopores in the Horn River Group fall into the 1–2 nm radius range, with a small proportion of mesopores between 2–8 nm. Point counts from SEM images confirm that of the porosity visible at this scale, interparticle porosity is dominant with limited intraparticle porosity and rare organic matter-hosted pores. Cross plots and multivariate statistical analysis demonstrate that in this unit, porosity is most closely related to mineralogy, with little correlation between porosity and total organic carbon (TOC) or thermal maturity. Together, these results suggest that silica abundance and clay content are the best predictors of porosity, and unlike many other North American shale plays, TOC and thermal maturity are not primary influences on porosity abundance; characteristics likely owing to a lower proportion of organic-matter pores in the Horn River Group of the study area. The identification of controls and predictors of porosity in the Horn River Group of the Northwest Territories is an essential step towards understanding hydrocarbon storage and potential reservoir character through the interval.