Abstract

Steam-assisted gravity drainage (SAGD) is the preferred thermal recovery method used to recover bitumen from Athabasca deposits in Alberta, Canada. In SAGD, steam injected into a horizontal injection well is forced into the reservoir, losing its latent heat when it comes into contact with the cold bitumen at the edge of a depletion chamber. Heat energy is transferred from steam to reservoir, reducing the viscosity of the bitumen, which flows under gravity toward a horizontal production well. Conduction is the main heat transfer mechanism in early SAGD, and reservoir thermal conductivity is a key parameter in conductive heat transfer. Conductive heat transfer occurs at a higher rate across reservoirs with higher thermal conductivity, which in turn affects the temperature profile ahead of the steam interface. Consequently, a reservoir with higher thermal conductivity will result in higher reservoir heating rates, and higher oil production rates. When the oil sands reservoir undergoes a temperature change from reservoir temperature to steam chamber temperature the thermal conductivity decreases up to 25% (depending on the initial reservoir and steam temperature), which affects the temperature profile and conductive heating within the reservoir. This study provides a modified Butler's model which includes a temperature-dependent thermal conductivity value. A simplified method is suggested using the thermal conductivity at average temperature of steam and reservoir will keep error under 1% for the range of SAGD applications. This novel approach is the first of its kind to incorporate a temperature-dependent thermal conductivity within the reservoir to a SAGD analytical model.

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