Changes

Wellbore effects dominate early test data. The end of wellbore effects is found using log-log plots of test data, which are compared to preplotted type curves, as illustrated in [[:file:pressure-transient-testing_fig1.png|Figure 1]]. The shapes of test data plots are also used to identify the reservoir type, such as homogeneous acting, naturally fractured, layered, or hydraulically fractured. Derivative type curves (basically the slope of a plot of pressure versus the logarithm of time) are particularly helpful for identifying reservoir type and wellbore effects, as shown in [[:file:pressure-transient-testing_fig2.png|Figures 2(a) and (b)]].

Wellbore effects dominate early test data. The end of wellbore effects is found using log-log plots of test data, which are compared to preplotted type curves, as illustrated in [[:file:pressure-transient-testing_fig1.png|Figure 1]]. The shapes of test data plots are also used to identify the reservoir type, such as homogeneous acting, naturally fractured, layered, or hydraulically fractured. Derivative type curves (basically the slope of a plot of pressure versus the logarithm of time) are particularly helpful for identifying reservoir type and wellbore effects, as shown in [[:file:pressure-transient-testing_fig2.png|Figures 2(a) and (b)]].

Traditional analysis is focused on semi-logarithmic plots of test data, with slopes of straight lines on these plots used to determine [[permeability]]. [[:file:pressure-transient-testing_fig3.png|Figure 3]] is a typical semi-log plot of flow test data, and [[:file:pressure-transient-testing_fig4.png|Figure 4]] is a typical semi-log plot of buildup test data. The “correct” semi-log straight line is indicated on these figures; the line is identified with the help of type curves (see “[[Production histories]]”). On the buildup test plot, shut-in bottomhole pressure is plotted versus the logarithm of the ratio of producing time, ''t''_p, plus shut-in time, Δ''t'', to shut-in time. This plot is called a ''Horner plot'', named for the person who proposed it in the petroleum literature.

Traditional analysis is focused on semi-logarithmic plots of test data, with slopes of straight lines on these plots used to determine [[permeability]]. [[:file:pressure-transient-testing_fig3.png|Figure 3]] is a typical semi-log plot of flow test data, and [[:file:pressure-transient-testing_fig4.png|Figure 4]] is a typical semi-log plot of buildup test data. The “correct” semi-log straight line is indicated on these figures; the line is identified with the help of type curves (see [[Production histories]]). On the buildup test plot, shut-in bottomhole pressure is plotted versus the logarithm of the ratio of producing time, ''t''_p, plus shut-in time, Δ''t'', to shut-in time. This plot is called a ''Horner plot'', named for the person who proposed it in the petroleum literature.

Simple equations allow us to estimate permeability and skin factor once the correct semilog straight line is identified and its slope, ''m'', is estimated. These equations apply to both drawdown and buildup tests. The following equations are used for oil wells:

Simple equations allow us to estimate permeability and skin factor once the correct semilog straight line is identified and its slope, ''m'', is estimated. These equations apply to both drawdown and buildup tests. The following equations are used for oil wells: