Open File Report 1993-21

Open File Report 1993-21

OFR 1993-21

Geochemical Studies - 3; Geochemistry of Some Alberta Shales and Associated Kerogen

Author(s) Hitchon, B. Date 1993-01-01

A set of 28 shales from the Alberta Basin, ranging in age from Late Cretaceous to Middle Cambrian, was studied with respect to their major and trace element composition, and the kerogen extracted from 25 of them for detailed analysis. This Open File Report contains the basic data on the shales and kerogen. It is not intended to report this information elsewhere.

Although the shales are widely scattered, on a volumetric basis the Upper Cretaceous is underrepresented and the Lower Cretaceous over-represented. The average for 24 non-calcareous shales from the Alberta basin is close to the average shale in geosynclines. A decrease in SiO� content with age suggest s a decrease in silt (quartz) content rather than a change in clay mineralogy. General statistics are provided for groups of shales based on the three crude oil families distinguished by previous authors I.e. Group 1: U. Cretaceous Colorado and post-Colorado reservoirs; Group 2: L. Cretaceous Mannville Group. Jurassic, Carboniferous and U. Devonian Wabamun Group reservoirs; Group 3: U. Devonian Winterburn and Woodbend Groups and Beaverhill Lake Formation reservoirs. For Cd, Cr, Mn, Fe, Co, Ni and Mo there is no significant difference among the three groups of shales. Sodium in formation water and crude oil increases with depth, whereas, for reasons not clear, Na in shales decreases. The sharp decrease in the contents of Zn, Cu and Pb with depth is associated with the increased salinity (chloride content) of the associated formation waters and may relate to the greater ease of removal of these elements from shales as chloride complexes of the metals.

The majority of the kerogen samples are Type III, the rest being Type II; with one exception they are low-S types. Using estimated maximum temperature from a previous study, it is suggested that there is a tendency for loss of both O and S with increased temperature and therefore a relative increase in N as a residual effect. With respect to the ESR properties of the kerogen, increased temperature results in increased spin concentrations, lower g-values, and wider lines. At any specific temperature, there is a wide range in the NMR aliphatic-carbon/aromatic-carbon ratio.