ABSTRACT

The Nordegg Member is one of the richest hydrocarbon source rocks in the Peace River Arch region. The Nordegg is highly radioactive, and can be identified by its characteristic signature on gamma-ray logs. The thickness of the Nordegg is generally 20 to 25 m. Its dominant lithology is dark grey to black limestone with minor calcareous shales. Analysis of over 200 core samples using Rock-Eval/TOC pyrolysis yielded Tmax values from 430°C to 460°C, Total Organic Carbon (TOC) contents ranging up to 28 per cent, and Hydrogen Indices (HI) ranging up to 800 mg HC/g TOC. Maturity increases in a southwesterly direction, from the subcrop edge toward the Foothills Belt.

Organic petrographic examination, using both reflected white light and ultra-violet light (fluorescence microscopy), revealed a high content of green to orange fluorescing (depending on thermal maturity) algal material. Other organic constituents include amorphous material and minor amounts of inertinitic fragments, consistent with HI/OI results from Rock-Eval analysis that indicate predominantly TypeI/II organic matter. Reflectance measurements made on bitumen found in fractures and voids within the rock suggest as many as three bitumen phases in some samples.

The biomarker signatures of several extracts from the Nordegg were determined using gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). Comparison of these results with GC and GC/MS data from oils reservoired in the Upper Triassic Worsley dolomite indicates that the Nordegg is a source for some of the Triassic-reservoired oils in the Peace River Arch area. The fine grained, organic-rich nature of the Nordegg Member, and its stratigraphic position within the basin allow this unit to act as both hydrocarbon source rock and seal for oils reservoired in porous units below the sub-Jurassic unconformity.

End_of_Record - Last_Page 178-------