Geological Atlas of the Western Canada Sedimentary Basin - Chapter 31

Chapter 31
Petroleum Generation and Migration in the Western Canada Sedimentary Basin

Authors:
S. Creaney - Imperial Oil Resources Ltd., Calgary
J. Allan - Imperial Oil Resources Ltd., Calgary
K.S. Cole - Imperial Oil Resources Ltd., Calgary
M.G. Fowler - Geological Survey of Canada, Calgary
P.W. Brooks - Geological Survey of Canada, Calgary
K.G. Osadetz - Geological Survey of Canada, Calgary
R.W. Macqueen - Geological Survey of Canada, Calgary
L.R. Snowdon - Geological Survey of Canada, Calgary
C.L. Riediger - The University of Calgary, Calgary

Introduction

The role of this theme chapter is to familiarize the reader with the current state of knowledge concerning the origin and history of petroleum within the Western Canada Sedimentary Basin. The previous atlas (McCrossan and Glaister, 1964) provided considerable stratigraphic information plus a chapter on formation fluids (Hitchon, 1964). The information contained in the 1964 atlas predated the development of tools that permit the convincing correlation of petroleum fluids to their source rocks and to their thermal regime of origin. In addition, the processes of petroleum alteration via biodegradation and water washing were poorly understood, leaving the origin of Western Canada's oil sands and heavy oil deposits unresolved.

The present contribution provides a summary of the petroleum systems that operate in the Western Canada Sedimentary Basin. It does so from the point of view of petroleum exploration as opposed to a detailed analytical geochemical approach. Thus, summary maps are presented with only sufficient data to illustrate oil-oil and oil-source correlations rather than exhaustive data compilations. These data are located elsewhere in the public literature and are referenced as appropriate.

The authors represent two groups working extensively on petroleum geochemistry in the Western Canada Sedimentary Basin and, as with all science, divergences of opinion do exist. Where these are manifest both arguments are presented. The information herein is drawn from a number of sources, principally Creaney and Allan (1990, 1992), Allan and Creaney (1991), Brooks et al. (1988, 1989, 1990), Osadetz and Snowdon (in press), Osadetz et al. (1991), Riediger et al. (1990 a,b), Riediger (1991) and Deroo et al. (1977).

When analyzing the petroleum systems of any sedimentary basin, especially one whose exploration history is as long as that of the Western Canada Sedimentary Basin, one objective is to understand the geographic and geological distributions of petroleum. Figure 31.1 comprises a pair of histograms showing original in-place conventional oil reserves versus reservoir age for the Western Canada Sedimentary Basin (B.C., Alberta, Saskatchewan). It is this distribution that this chapter seeks to explain. The current state of knowledge of thermal gas-source rock correlation is too poor to make discussion of the geological distribution of gas reserves meaningful in the petroleum system context. Gas occurrence and origin are discussed for certain specific examples wherever the data make this possible.

Formation water geochemistry is not discussed in any detail in this chapter and the reader is referred to Hitchon (1964), and Hitchon et al. (1990) for detailed discussions and more reference material on this topic.