Characterization of immature oil shales from the Cretaceous Second White Specks Formation in Saskatchewan and Manitoba, Canada

Abstract

The Cretaceous Second White Specks Formation is an organic-rich marine mudstone rich in calcareous coccoliths and fecal pellets that form an immature oil shale deposit. Corehole and outcrop oil shale samples, taken from western Manitoba and across Saskatchewan, Canada, were analyzed by organic petrography (reflected white and UV light), Rock-Eval pyrolysis, and elemental analysis (boron and sulfur) to characterize the oil shales in relation to their depositional environment and hydrocarbon generating potential. This study revealed that the oil shales all contain small amounts of sapropelite/huminite and inertinite. Inertinite consists of particles deposited from a terrigenous environment and have higher %Ro > 0.4, referred to as secondary inertinite. Primary inertinite is associated with the roots of marine grass and seaweeds. Fluorescing marine telalginite, Nostochopsis alginite, dinoflagellates, liptodetrinite, matrix bituminite, and chlorophyllinite are also present. Based on a detailed geological, sedimentological, geochemical, and organic petrological investigation, the oil shales were divided into three depositional facies: coastal marine (B:60 ppm), shallow marine (B: ∼80 ppm), and open marine (B:113 ppm). The oil shales are immature (Tmax = 398–425 °C) across the entire study area with %Ro of 0.20–0.27. The coastal marine facies oil shales have high TOC content (ave. = 10.4 wt%), S2 ave. = 54.9 mg HC/g TOC, HI ave. = 480 mg HC/g TOC, low Boron (ave. = 47 ppm) content and can generate an average of 43 lit/tonne of hydrocarbons. On the other hand, the shallow marine facies oil shales have average TOC of 8.1 wt%, average S2 of 41.2 mg HC/g TOC, and are much higher in B content (ave. = 80 ppm). The open marine facies oil shales have low TOC (ave. = 0.94 wt%), S2 averages 1.3 mg HC/g TOC, and HI averages 189 mg HC/g TOC. They have much lower hydrocarbon potential (ave. = 1.50 lit/tonne) but are high in B content (ave. = 109 ppm). Overall, it was concluded that in one specific area in the Pasquia Hills of northeastern Saskatchewan, the Second White Specks oil shales are shallow (<100 m deep), thick (10–45 m), have TOC of >7 wt%, and can generate >80 lit/tonne of hydrocarbon. This makes them suitable for ex-situ extraction.