Microstructural characterization of a Canadian oil sand

Abstract

The microstructure of oil sand samples extracted at a depth of 75 m from the estuarine Middle McMurray formation (Alberta, Canada) has been investigated by using high resolution 3D X-Ray microtomography (\(\mu\)CT) and Cryo Scanning Electron Microscopy (CryoSEM). \(\mu\)CT images evidenced some dense areas composed of highly angular grains surrounded by fluids that are separated by larger pores full of gas. 3D Image analysis provided in dense areas porosity values compatible with in-situ log data and macroscopic laboratory determinations, showing that they are representative of intact states. \(\mu\)CT hence provided some information on the morphology of the cracks and disturbance created by gas expansion. The CryoSEM technique, in which the sample is freeze fractured within the SEM chamber prior to observation, provided pictures in which the (frozen) bitumen clearly appears between the sand grains. No evidence of the existence of a thin connate water layer between grains and the bitumen, frequently mentioned in the literature, has been obtained. Bitumen appears to strongly adhere to the grains, with some grains completely being coated. The curved shape of some bitumen menisci suggests a bitumen wet behaviour.