A New Semi-Analytical Model for Thermal Recovery Processes

ABSTRACT Gravity drainage of heated oil in thermal recovery processes is an important mechanism, often resulting in high sweep efficiency with economical rates. A semi-analytical model is developed to predict production rate from heavy oil reservoirs under non-isothermal gravity drainage. This work improves upon the previous ones by accounting for the unsteady-state effects in the heat flow process as well as considering the effect of the moving interface, in cylindrical coordinates. The solution incorporates a Heat Integral Method (HIM) to approximate the 2-D heat transfer in the reservoir. The shape of the oil-steam interface is found as a part of the solution. The predictions of the model are validated against published experimental results. Examples for two Californian heavy oil reservoirs indicate that economical rates with high sweep efficiencies can be obtained from reservoirs under gravity drainage, especially when the surface area of the production well exposed to the reservoir is increased, e.g. by implementing horizontal producers.