Bentonite seams of varying thicknesses, from a few millimetres to about 30 cm, are found at depths of 200-300 m within the Belle Fourche Formation and Second White Specks unit in the Cretaceous Colorado Group in the Cold Lake area of Alberta, which is one of four exploration sites for extraction of heavy oil in Alberta. Thermal heavy oil recovery processes in oil sand reservoirs, such as cyclic steam stimulation and steam-assisted gravity drainage, cause casing impairment and failure in the overlying Colorado Group shales. Based on the results from triaxial compression and direct shear box tests on bentonite seam samples, the material displays not only low stiffness and friction angle, but also pronounced creep. Results from numerical analyses of case studies illustrate that the shear slip mechanism along these bentonite seams is admissible in the field under steam stimulation processes. The slip mechanism is mainly attributed to the huge contrast in deformation moduli and creep between the soft bentonite seam and the stiff Colorado Group shales, rather than due to the low frictional resistance derived from the bentonite seam.