This paper presents analytical algorithms to calculate ultimate recovery factors for radial flow systems. The approaching method is similar to the well-recognized Buckley-Leverett equations, but it's accurate for matured fields, especially peripheral water-flooding reservoirs.

Buckley-Leverett displacement equations have been derived strictly from linear flow systems, and have been verified by linear flow experiments only. However, nowadays, it's very common to observe multiple water injectors drilled around producers to enhance the recovery factor in mature fields. New analytical equations that consider non-linear flow patterns are more appropriate for these types of operations.

The new equations proposed in this paper have been verified with real field data. The original Buckley-Leverett equation generally results in much lower recovery factors that barely match the cumulative production. Consequently, the estimated ultimate recovery (EUR) by volumetric methods tends to be too low. As a result, the production projections according to match this EUR are not reasonable when compared to the historical performance of the wells and Decline Curve Analysis (DCA). The proposed analytical model improves the prediction of reservoir performance. It works as an important supplement to the Buckley-Leverett method for oil fields worldwide.

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