An experimental study was conducted to investigate the surface characteristics of an oil sand fracture and its mechanical response to an increasing confining pressure. The oil sand fracture was induced in core samples along the axis of the sample using the Brazilian tension test. A Computer Assisted Tomography (CAT) scanning analysis was performed before and during the application of confining pressure to determine the fracture geometry during the closure process. The fracture was shown to be a variable aperture system with (when considering possible fluid conductance) surface roughness and tortuosity becoming increasingly important as the fracture closed. The mechanical response showed the importance of surface roughness and the resultant contact area on the ability of the fracture to withstand a confining pressure.
Heavy oil and bitumen are a major energy resource in Canada, Venezuela, and elsewhere. The challenge in developing this resource is the difficulty in recovering these highly viscous substances. Thermal recovery has become an accepted method with steam-based recovery drawing much attention. Steam-based recovery methods involve the injection of steam into the reservoir to heat up the reservoir, lowering the viscosity of the bitumen, which increases production rates. Cyclic steam- based recovery processes have become common practice in the thermal operations of the Cold Lake heavy oil reservoirs (Boone et al. 1993). The steam injection approach used at Cold Lake encourages fracturing of the reservoir each steam cycle, exploiting the permeability of the fracture instead of relying on a layer of bitumen depleted, permeable oil sand. The high hydraulic conductivity of the fracture enables heat transfer to take place further away from the well, thus, accessing more undisturbed reservoir material instead of depositing most of the heat in a previously heated and bitumen depleted area of the reservoir. In order to optimize this steaming approach an understanding of the medium used to carry the heating agent, the fracture, is essential. The geometry of the fracture, characterized by surface roughness, aperture distribution and tortuosity, plays a key role in the permeability of the fracture as well as the flow channels available to the injected mass. A detailed picture of an oil sand fracture, its surface characteristics and mechanical behaviour under a varying confining pressure is needed to better understand and possibly exploit the flow phenomena taking place during and after the hydraulic fracturing process of steam stimulation. According to the authors knowledge, no work is currently available characterizing an oil sand fracture or proving that fractures in this material behave in a similar manner as to what has been previously studied in rock fractures (Barton et al. 1985; Brown and Olsson 1993; Hakami and Barton 1990). The following study presents an experimental, physical characterization of an oil sand fracture using a Computer-Assisted Tomography (CAT or CT) scanning analysis to visualize the fracture geometry and closure response. The results of this procedure give an understanding of an oil sand fracture's aperture distribution, surface roughness, as well as its mechanical behaviour under an increasing confining pressure.
