Geochemical constraints on models for secondary petroleum migration along the Upper Devonian Rimbey-Meadowbrook reef trend in central Alberta, Canada

Abstract

The Upper Devonian Rimbey-Meadowbrook reef trend of central Alberta, Canada, is one of the classical examples that was originally used to support Gussow's model of differential hydrocarbon entrapment. However, the clear discrepancies existing between the ideal hydrocarbon distribution predicted by this model and the one actually observed led to several alternative geological models, most of which have not been constrained by organic geochemical data. The present study uses a wide range of bulk and molecular parameters to determine the oil source characteristics and thermal maturity along the reef trend. The concentrations and isomeric distributions of alkylcarbazoles and non-alkylated benzocarbazoles in oils are employed to study petroleum migration pathways and to constrain the existing secondary petroleum migration models. The data indicates that Gussow's principle is generally applicable, as the oils in the up-dip direction generally have longer implied migration distances although this is not always the case. Other factors not recognized previously, such as the presence of two subfamilies of the Duvernay Formation sourced oils, may also have contributed significantly to the discrepancies in the oil and gas distributions between the model predictions and the actual observational data.