ABSTRACT

The use of chemical tracers, determined by the analysis of reservoired oils and associated gases, to quantify petroleum migration processes could significantly improve the constraints for basin fluid models and help identify petroleum secondary migration pathways. This paper reviews the geochemical controls on one potential molecular tracer class (pyrrolic nitrogen compounds), particularly the effect of source and maturity. Three case studies illustrate how to utilize the changing concentrations of these compounds in related suites of migrated petroleums to constrain regional fluid models and to define small, efficient channels where petroleum has migrated from source rocks to traps in the Williston Basin. The first case deals with the Winnipegosis petroleum system in southeastern Saskatchewan, where oils previously thought to be sourced locally are shown to have the longest migration distances among a suite of related oils. The second case concerns the recent major Ordovician discoveries also in southeastern Saskatchewan, where two types of Ordovician oils present in a restricted area are demonstrated to have vastly different migration distances, the less mature oils being generated locally and the more mature oils being sourced from farther down-dip in the basin. The third case compares the geochemistry of unexpelled oils with conventionally reservoired oils from the Bakken petroleum system where the prerequisites for the application of pyrrolic nitrogen data are illustrated.