Elements of a Stratigraphic Framework for the McMurray Formation in South Athabasca Area, Alberta

Abstract It is a common belief that the sand bodies constituting the potential reservoirs in the McMurray Formation are extremely heterogeneous and almost impossible to correlate. This makes exploration difficult and limits recovery schemes to the few areas that contain thick channel sands. A new stratigraphic framework is proposed for the McMurray Formation of south Athabasca. Detailed log correlations from 1700 wells demonstrate that stacked, prograding, shoreface parasequence sets that can be regionally correlated over the entire southern Athabasca Oil Sands Deposit. These parasequence sets represent highstand systems tracts. They are best preserved in the south, and are also preferentially preserved towards the top of the McMurray Formation. However, the dominant depositional elements in the basin are lowstand channels incised into the parasequence sets. During sea level rise, these channels are filled with a transgressive estuarine facies complex, consisting dominantly of sandy to muddy estuarine point bars. The basal fill of some of the deeper channel valleys consists of freshwater fluvial point bars. Statistical facies analysis, using clustering techniques and Markov analysis, differentiates a large database of facies descriptions into three major successions that correspond closely with the proposed stratigraphic framework for the McMurray Formation. These successions are interpreted as: 1) a simple coarsening-upward shoreface succession 2) a complex of interrelated channel fill deposits and 3) rooted paleosols. The top of the McMurray Formation appears to be an erosion surface and may be a sequence boundary.