A model has been formulated for estimating the oil production during the mature phase of a steam injection process. This model assumes that complete steam overlay has occurred and that subsequent drainage of oil is accelerated because of the viscosity reduction in the heated oil phase. The predicted oil production history usually shows a rate which declines linearly at early times, depending on the initial oil level in the reservoir, and gradually declines toward zero at long times. The model has been applied to various field cases from the SPE literature. In most cases the model predicts results which are relatively close, usually much better than an order of magnitude, to the available field observations. Adjustment of a parameter such as permeability to take into account specific field behavior is usually sufficient to obtain good agreement in the rate as a function of time for most of the field cases studied. Deviations may be expected from the predicted behavior in those cases where additional mechanisms besides gravity drainage are operative or where there is non-uniform heating of some of the wells in a given field.

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