Relationships between Porosity, Organic Matter, and Mineral Matter in Mature Organic-rich Marine Shale of the Belle Fourche and Second White Specks Formations in Alberta, Canada
Indiana University Bloomington, Department of Geological Sciences Bloomington, IN, USA
This study presents an evaluation of the organic and inorganic composition and their relationship to pore characteristics of an emerging hybrid source rock/reservoir shale play in the Upper Cretaceous Second White Specks and Belle Fourche Formations in central Alberta, Canada. Nineteen samples from a 77.5 m-long core were analyzed using organic petrography, organic geochemistry, several methods of pore characterization, and X-ray powder diffraction. Based on petrographic examinations the organic matter represents marine Type-II kerogen with limited terrestrial input. Vitrinite reflectance Ro (0.74-0.87 %) and Tmax values (438-446 °C) indicate a mid-maturity within the oil window. The remaining hydrocarbon potential (S2 peak value ranges from 2.1 to 6.5 mg HC/g rock) is relatively poor. However, the present-day remaining TOCpd content is still fairly high (1.7-3.6 wt. %). The studied section is a tight reservoir with an average Swanson permeability of 3.37·10-5 mD, total porosity between 2 and 5 vol. % (average 3 vol. %), and total pore volume between 0.0065 and 0.02 cm3/g. The upper part of the Belle Fourche Formation, with slightly elevated porosity values (3.5-5.0 vol. %), likely represents the interval with the best reservoir properties in the studied core interval. Porosity is variable within the section and primarily depends on the mineralogical composition, whereas organic matter does not appear to have a measurable influence on porosity. Organic matter and clays appear to be dominant contributors of microporosity. Mesoporosity shows an association with quartz, feldspar, and clays, whereas macropores are likely linked to carbonates.
AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects