Source Changes in McMurray Formation and Effects on Recovery of Bitumen in Athabasca Oil Sands

Marian M. Smith, Robert Ehrlich, Arvid Hardin

The Lower Cretaceous McMurray Formation of Alberta hosts an estimated 74 million bbl of oil that are minable and an additional 551.9 billion bbl of oil that will have to be recovered by heavy-oil extraction methods. Bitumen recovery by the Clark hot-water extraction method varies within and between depositional environments, depending primarily on the makeup (size, shape, and composition) of the sand. A distinct change in the sediment source from quartzose channel sands to more cherty and glauconitic marine sands is shown by Fourier grain-shape analysis of quartz and compositional grain counts. A size and compositional relationship exists in marine sands of the McMurray Formation such that sand grains burial greater than 63 µm are predominantly quartz, whereas grains less than 63 µm are predominantly chert. The chert has a high surface area, which causes oil to remain with the grains, thus reducing primary recovery. Multiple regression analysis of size, shape, and data regarding oil, water, and solids showed that shape (i.e., irregularity and high surface area) was the most important factor in predicting primary recovery of bitumen in the Athabasca oil sands. Change in source (with finer grains and more irregular chert) in the marine zone is the underlying cause for reduced recovery in that zone. Size, shape, and c mpositional analysis of both the oil sands and the solids from the process streams of the hot-water extraction process show how changes in sediment makeup affect primary and secondary bitumen recovery.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.