Dynamic modeling of solution-gas drive in heavy oil reservoirs
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2007
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Abstract
Some heavy oil reservoirs in Canada show atypically high production rates and high primary oil recoveries under solution-gas drive. Much attention has been given to the anomalous behaviour observed in such heavy oil reservoirs, and several models have been suggested to explain these anomalies. There are possibly two classes of effects responsible for the unusual behaviour of solution-gas drive in heavy oil reservoirs, including fluid effects and rock/geomechanical effects. However, since the role of geo-mechanics has been studied by several investigators, this study focuses exclusively on fluid effects. Two main features are different between solution-gas drive in heavy oils and the traditional view of solution-gas drive as seen to function in light oil reservoirs. In heavy oils, the concentration of gas in the oil can be greater than the equilibrium value, giving rise to the oil becoming supersaturated. In addition to this, recovery and gas mobility show rate dependent behaviour in heavy oils. Both of these effects are taken into consideration in this study. In this study, a dynamic model is developed which captures many important processes that affect heavy oil recovery. The non-equilibrium early time behaviour is modeled by introducing a kinetic equation describing the rate of evolution of solution gas into free gas. The equation is derived based on a phenomenological analysis which takes into account bubble nucleation and bubble growth. A second component of this model captures the low gas mobility in heavy oil reservoirs and its dependency on viscous forces. To account for the effect of viscous forces on gas mobility, the proposed relative permeability function depends not only on gas saturation but also on local oil phase velocity and oil viscosity. While many of the previously existing models apply several kinetic equations associated with a large number of parameters, it has been shown that the modifications suggested in this study enable predicting many of the unusual behaviours observed in solution-gas drive in heavy oil reservoirs, using only one kinetic equation with a smaller number of fitting parameters.
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Bibliography: p. 102-108
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Citation
Shahvali, M. (2007). Dynamic modeling of solution-gas drive in heavy oil reservoirs (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/1198