New shape factors are developed for bounded reservoirs produced by wells operating at constant bottomhole pressure. The new shape factors should replace Dietz shape factors (constant rate shape factors) when calculating the productivity of wells producing at constant bottomhole pressure; thus obtain a more reliable long term production forecast. Although the constant pressure and constant rate shape factors are conceptually different, they are close in value for regular shapes (square) with well in the center. However, for irregular shapes and off-centered wells, the difference is significant. The use of constant rate shape factors for predicting the performance of wells producing at constant bottomhole pressure results in over-estimation of well productivity.

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