Geomechanical properties of heavy oil sands greatly impact our ability to model and implement most heavy oil recovery processes. Many heavy oil recovery processes involve the injection of fluids (or reduction in stresses to allow fluids to flow) and thus the stress paths during at least part of the process is extensional. This paper investigates the transport and mechanical properties of oil sands under fluid injection and the subsequent stress reduction and dilation that ensues. We find that very significant dilation occurs in the sands during injection and that standard triaxial tests, although showing significant dilation, may not fully represent the stress path and deformation that reservoirs undergo during injection. We find that the interbedded mudstones that are often found in fluvial and tidal depositional environments of Canadian oil sands behave similarly to the bitumen saturated oil sands but with greater amounts of dilation over similar stress paths. We also find that permeability to water of both the oil sands and mudstones increases dramatically along these extensional stress paths.
The understanding of the geomechanical properties of Canadian heavy oil sands is important for modeling and implementation of most heavy oil and bitumen recovery processes. The injection of steam at high pressure for processes such as Cyclic Steam Stimulation (CSS) and Steam-assisted Gravity Drainage (SAGD) causes significant thermal and mechanical strain in the oil sand reservoir. The production of significant sand in Cold Heavy Oil Production w/Sand (CHOPS) causes unusual deformation patterns (generally referred to as wormholes) in the subsurface and corresponding decreases in stresses near the flow channels. Although many papers have been written on the geomechanics of oil sands (Agar et.al., 1987; Dusseault and Rothenburg, 1988; Kosar et.al., 1987; Samieh and Wong, 1997; Touhidi-Baghini, 1998; Tremlay et.al., 1997; Wan et.al., 1989; Wong, 2003; Wong et.al., 1993) much of the work has focused on classical compaction and triaxial compression or shear box testing of the oil sands. However, much of the deformation in the sands during recovery processes is dilative or extensional behavior due to fluid injection or sand production causing significant reduction in effective stresses. This paper will look at the mechanical and transport properties of some Canadian heavy oil sands under extensional stress paths due to fluid injection and how some of the unique properties of Canadian heavy oil sands impact the behavior of the sands and thus the effectiveness of many heavy oil recovery processes.
Most Canadian heavy oil sands lie in a belt just east of the Rocky Mountains in Alberta and the western parts of Saskatchewan . Most of the producible heavy oil is contained in unconsolidated sand reservoirs which are fluvial or tidal in origin and are deposited less than 600m from the surface. Many of the sands are moderately to well sorted but highly angular. Although shallow, the sands tend to be highly “overconsolidated” from a geotechnical perspective due to 2 km of ice loading during previous ice ages and small to moderate uplift since then.
