Changes

Buildup tests are appropriate at virtually any time in the life of a well because they simply require that the well be shut in. Buildup tests have the advantage that the rate (zero) is much more easily controlled than in a “constant rate” flow test. For this reason, buildup tests are overwhelmingly the preferred type of pressure transient test in practice.

Buildup tests are appropriate at virtually any time in the life of a well because they simply require that the well be shut in. Buildup tests have the advantage that the rate (zero) is much more easily controlled than in a “constant rate” flow test. For this reason, buildup tests are overwhelmingly the preferred type of pressure transient test in practice.

===How the tests are analyzed===

===How the tests are analyzed===

[[file:pressure-transient-testing_fig3.png|left|thumb|{{figure number|3}}Typical flow test data graph.]]

[[file:pressure-transient-testing_fig4.png|thumb|{{figure number|4}}Typical buildup test graph (Horner plot).]]

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.