Geotechnical properties of bentonite seams — its effects on casing integrity under steam injection in Cold Lake, Alberta

Abstract

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.

Quantifying structural states of soft mudrocks

“…As a major overburden rock above the oil sands reservoirs in Cold Lake area, the Colorado group shale consists of up to 180 m thick series of marine shales and minor siltstones, with some occasional ironstone, concretions, and bentonite layers. Six formations of Colorado Group shales were found in the Cold Lake area, and these six units in ascending order are Joli Fou Formation, Viking Formation, Westgate Formation, Fish Scales Zone (or unit or marker), Belle Fourche Formation, and Second White Specks (SWS) unit [ Wong et al ., ]. SEM images showing the hexagonal symmetry fabric of Colorado shale were displayed in Wong et al [].…”

Experimental Studies of Thermally Induced Deformation and Fracture Generation in Clay Shale

“…The samples belong to the Joli Fou formation at a depth of 300 meters, shown in Fig. 1 (Wong et al 2011). The Joli Fou formation is extremely widespread, and is distributed throughout the subsurface, except in parts of northwestern Alberta, Canada and northeastern British Columbia, Canada.…”

“…Thermally induced deformation and failure in shale can pose an impact on casing and caprock integrities (Collins et al 2013;Miyazawa et al 2008;Wong and Yeung 2006;Yuan et al 2013). Most previous investigations focused on the mechanical properties of the clay shale (Gautam and Wong 2006;Wong et al 2011;Wong et al 2008). However, limited experimental work has been conducted to investigate the thermal response of clay shale under thermal operation conditions.…”