Abstract

In Part 1 of this study (SPE 165457-MS) a permeability enhancement at the edge of steam chamber where the oil sand has been sheared under thermal stimulation was described and an increase in oil drainage rates was calculated for different conditions. Finally, a modified Butler's Theory that includes geomechanical effects was described.

Since heat transfer mechanisms are pivotal to the SAGD process and there are some doubts on the behaviour of the undrained zone at the edge of SAGD steam chamber in this study thermodynamics of undrained zone is discussed and new mechano-thermal equations are described. At the edge of steam chamber heat energy is transferred from steam to reservoir, reducing the viscosity of the bitumen, which flows under gravity toward a horizontal production well. Some of the heat transferred into the reservoir is used to increase the temperature of the reservoir, and some is stored as strain energy associated with the thermal stress field. The classical approach to exploring heat transfer studies in the SAGD industry is designed to satisfy only the "conservation of energy". Therefore, there is a lack of understanding of strain energy absorbed within the reservoir, and its effect on temperature variation inside the reservoir. The aim of the present work is to introduce a thermodynamic model to explore the effects of strain energy on temperature within the reservoir. This study explores the negative effect of developed stress field on heat transfer normal to the steam chamber interface. The novelty of this approach is the fact that it fully honours the energy equation. This study suggests the strain-energy number (NΔ) as a new dimensionless number representing an importance of the strain energy effect on the temperature profile within the reservoir. The results obtained from this study reveal that it is suitable to use Butler's theory and to exclude the strain energy effects in heat transfer in the SAGD process. This study uses both thermodynamic approach and pressure front evaluation to argue the current practice of suggesting no permeability enhancement occurrence beyond the 12 m from the steam interface suggested by Li et al. (2004) based on the bitumen viscosity greater than 20,000 cP. This study proposes using one tenth-length of pressure front for drained zone which is beyond the temperature front advancement. Knowing that the shear is mostly induced within temperature front, geomechanical effects within the reservoir can be studied suggesting drained condition.

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