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MODELING OF GRAVITY EFFECTS IN STREAMLINE-BASED SIMULATION FOR THERMAL RECOVERY

Gravity effects are more prominent in thermal recovery simulations due to larger densitydifference between phases. Historically, the streamline method has been unable toaccount for gravity effects. This is a result of assuming that the fluid path follows thestreamline path and therefore no communication among streamlines. However with gravity,a fluid pathline is different from a fluid streamline. Each phase can move vertically asa result of the gravity segregation effect in addition to the flow along streamline.Gravity effects are accounted in the streamline method by an operator splitting technique.The idea is to isolate the convective flow from diffusion due to gravity for separatesolutions. The convective part is calculated along the common streamline trajectories andthe diffusion part is determined by the direction of gravity. While this has been done successfullyfor isothermal problems, it is still a challenge to obtain both accuracy and efficiencyfor non-isothermal flow. This paper further examines the mixed streamline methodwith an operator splitting technique for this class of problems. The pressure equation fordefining streamlines was derived by summing up the mass conservation equations. Then,the mass and heat transport equations in terms of the streamline time-of-flight coordinatewere solved for each streamline. A gravity step will be followed by solving the segregationequations over the dimensional grid. For simplification of modeling, heat was assumed totransfer by convection only, of which direction is parallel with the flowing phases and theinfluence of temperature in the simulation model is through changes in fluid viscosity only.The proposed approach was tested through simulation of heavy oil recovery by means ofhot waterflooding. The results were verified with those of a commercial fully implicit thermalsimulator.