The late cretaceous Belle Fourche and Second White Specks formations in west-central Alberta, Canada, as an emerging hybrid source rock/reservoir shale play

Organic-rich mudstones with up to 10 wt. % total organic carbon (TOC) from seven sediment cores in west-central Alberta encompassing the upper Belle Fourche and lower Second White Specks Formations in the Western Canada Sedimentary Basin are being evaluated as a hybrid source rock/reservoir shale play. Geochemistry and organic petrography indicate a normal marine paleoenvironment with deposition of kerogen Type II based on the predominance of marine alginite and amorphous organic matter, limited amounts of terrigenous vitrinite and inertinite macerals, and the presence of marine fossils. The prevalence of short-chain n-alkanes (n-C13 to n-C19), a general predominance of C28 -alphabetabeta(H)-20S steranes, and small concentrations of oleanane confirm the dominantly algal and planktonic origin of organic matter. The thermal maturity increases westward across Alberta with two thermally immature cores (∼0.43% Ro vitrinite reflectance), one early mature core (∼0.65% Ro), and four cores representing mid-mature stages (∼0.78 to 0.90% Ro). A combination of helium porosimetry with low-pressure CO2 and N2 adsorption techniques was used to quantify porosity. The total porosity decreased from ∼10 vol. % to ∼1.0 vol. % (from ∼0.05 cm3/g to ∼0.005 cm3/g) along the maturation sequence. In general, organic matter is the strongest contributor to microporosity (with <2nm pore diameter). Overall, inter- and intraparticle pores in quartz contribute to greater abundance of micro-, meso- (2-50 nm O diameter), and macropores (>50 nm O), while the increasing content of clay minerals (illite, kaolinite, and chlorite) enhances both micro- and mesopore volumes. In contrast, carbonates (calcite and dolomite) seem to have a negative effect on porosity volumes in the measured shales. All thermally mature cores show good remaining hydrocarbon potential (2-48 mg hydrocarbon/g rock) and are dominantly oil prone as suggested by maceral compositions. Therefore, the Belle Fourche and Second White Specks Formations represent potential targets for unconventional light shale oil production.