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Thermal Pressurization in EM-SAGD Projects

  • Author(s) / Creator(s)
  • Inductive methods such as Electromagnetic Steam-Assisted Gravity Drainage (EM-SAGD) have been identified as a technically and economically feasible recovery method for shallow oil sands reservoirs with overburdens of more than 30 meters (Koolman et al., 2008). However, in EM-SAGD projects, the caprock overlying oil sands reservoirs is also electromagnetically heated along with the bitumen reservoir. Since permeability is low in Albertan thermal project caprock formations (i.e., the Clearwater shale formation in the Athabasca deposit and the Colorado shale formation in the Cold Lake deposit), the pore pressure resulting from the thermal expansion of pore fluids may not be balanced with the fluid loss due to flow and the fluid-volume changes due to pore dilation. In extreme cases, the water boils and the pore pressure increases dramatically as a result of the phase change in the water, causing profound effective stress reduction. Once this condition is established, pore pressure increases can lead to shear failure of the caprock, the creation of micro-cracks and hydraulic fractures, and to subsequent caprock integrity failure. It is typically believed that low permeability caprocks impede the transmission of pore pressure from the reservoir, making them more resistant to shear failure. In cases of induced thermal pressurization, low permeability caprocks are not always more resistant. In this study, analytical solutions are obtained for temperature and pore pressure rises due to the constant electromagnetic heating rate of the caprock. These analytical solutions show that pore pressure increases due to electromagnetic heating depend on permeability and compressibility of the caprock formation. For stiff or low-compressibility media, thermal pressurization can cause fluid pressures to approach total confining pressure, and shear strength to approach zero for low cohesive units of the caprock (units of the caprock with high silt and sand percentage) and sections of the caprock with pre-existing fracture with no cohesion (i.e., thermal liquefaction).

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  • Type of Item
    Research Material
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  • License
    Attribution 4.0 International