From Advanced Reservoir Engineering
1.5 Pressure Derivative Method
The type curve approach for the analysis of well testing data was developed to allow for the identification of flow regimes during the wellbore storagedominated period and the infiniteacting radial flow. As illustrated through Example 1.31, it can be used to estimate the reservoir properties and wellbore condition. However, because of the similarity of curves shapes, it is difficult to obtain a unique solution. As shown in Figure 1.49, all type curves have very similar shapes for high values of C _{D}e ^{2 s} which lead to the problem of finding a unique match by a simple comparison of shapes and determining the correct values of k, s, and C.
Tiab and Kumar (1980) and Bourdet et al. (1983) addressed the problem of identifying the correct flow regime and selecting the proper interpretation model. Bourdet and his coauthors proposed that flow regimes can have clear characteristic shapes if the pressure derivative rather than pressure is plotted versus time on the log log coordinates. Since the introduction of the pressure derivative type curve, well testing analysis has been greatly enhanced by its use. The use of this pressure derivative type curve offers the following advantages:

Heterogeneities hardly visible on the conventional plot of well testing data are amplified on the derivative plot.

Flow regimes have clear characteristic shapes on the derivative plot.

The derivative plot is able to display in a single graph many separate characteristics that would...
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