Analytical models to predict the performance of thermal recovery processes are useful tools for preliminary forecasting purposes and sensitivity studies and provide a better insight than simulation models into the physics of thermal processes. Classical models such as Marx and Lagerheim (1959), Willman (1961) and Farouq Ali (1971) are used extensively for steam-flood performance prediction. Several studies have been conducted to develop the theory for the estimation of the radius of the heated zone. This radius is important for computing the volume of recoverable oil, as well as to determine well spacing in steamflooding and cyclic steam stimulation. This work presents an analytical model to estimate the radius of heated zone in either conductive or conductive-convective heat transfer mechanisms, which mainly occur in Steam-Assisted Gravity Drainage (SAGD) and Cyclic Steam Stimulation (CSS) respectively. The heat flow equation was combined with mass and momentum convective transport equations in a porous medium, in an effort to correlate the temperature front velocity to the steam advancing front velocity. As the saturation front velocity is known from classical Buckley-Leverett transport equation, at each instant we investigated the transport distance of the heat front in a radial homogenous reservoir. The theoretical model takes gravity into account, but neglects the capillarity, and there is no longer the assumption of piston-like steam drive. CMG-STARS thermal simulation and COMSOL Multiphysics are used to compare and verify analytical model results. The improved model is superior to previous models used to calculate the radius of heated zone and the analytical results are in good agreement with the simulation results.

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