Effects of organic and mineral matter on reservoir quality in a Middle Triassic mudstone in the Canadian Arctic

Three main OM fractions are identified: i) light free hydrocarbons, ii) medium to heavy fluid-like hydrocarbon residue (FHR), and iii) kerogen and solid bitumen. The kerogen (allo- and autochthonous) and solid bitumen fraction, which is dominated by solid bitumen, occurs in two petrographically observable forms: matrix and lump solid bitumen. Matrix bitumen is primarily disseminated within the clay-rich matrix and fills smaller pores, whereas lump solid bitumen fills larger pores. TOC has a negative correlation with porosity indicating that it occupies pore space, with a detrimental effect on hydrocarbon storage and flow at the present level of thermal maturity. However, thermally overmature areas of the Murray Harbour Formation may have increased microporosity within the solid bitumen network which could provide additional adsorption sites for generated gas within the reservoir. Macro- and micro-scopic phosphate nodules (likely high-density apatite mineral) appear throughout the interval, and under fluorescence microscopy, are observed to retain light free hydrocarbons and FHR. A strong positive correlation between porosity and grain density suggests that these nodules contribute to porosity and provide capacity for hydrocarbon storage within the rock. This important observation can be applied to other phosphate-rich mudrock plays, including the coeval Doig Formation Phosphate Zone in the established Alberta Basin, to potentially identify and exploit prolific zones.