Abstract

The South Pit oil sands mine is located on the Fort Hills lease, in northern Alberta, Canada. The mine produces bitumen from the interbedded, poorly lithified sandstone and mudstone of the Lower Cretaceous McMurray Formation. The McMurray Formation is informally subdivided into the lower, middle, and upper members, representing deposition in fluvial, estuarine, and deltaic environments, respectively. The middle McMurray Formation hosts the majority of bitumen reserves and features complex internal geometry. It has been interpreted to be deposited as a series of large, tidally influenced point bars consisting of cross-stratified sandstone beds overlaid by interbedded sandstone and mudstone (i.e. inclined heterolithic stratification; IHS). Understanding the shape and length of the McMurray mudstone beds is essential as the mudstone beds act as either “baffles” or “barriers” to steam flow during Steam Assisted Gravity Drainage (SAGD) — in situ bitumen recovery method for underground reservoirs. The observations conducted in the South Pit mine indicate that the facies D50 value (median grain size) correlates well with mudstone bed architecture. In accord with these observations, a simple facies model was developed to predict the shape and length of the McMurray mudstones based on the facies D50 values. Additional evidence obtained from cores and dipmeter logs corroborates the proposed facies model.