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Line 33: − − [[file:pressure-transient-testing_fig1.png|thumb|{{figure number|1}}Type curve that identifies the end of wellbore effects.]] − − [[file:pressure-transient-testing_fig2.png|thumb|{{figure number|2}}(a) Derivative type curve used to match derivatives of test data. (b) Shapes of derivatives of test data for various reservoir conditions.]] − − [[file:pressure-transient-testing_fig3.png|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).]]+ + + + + + Line 79:
Line 78: − − [[file:pressure-transient-testing_fig5.png|thumb|{{figure number|5}}(a) Typical buildup curve shape with flow barrier, (b) Doubling of slope on Horner plot for well near barrier.]]
→Multi-rate flow tests
==Multi-rate flow tests==
==Multi-rate flow tests==
These tests are run much like single-rate tests, except that the rate is changed by discrete amounts one or more times while the test continues. An example of this type of test is a flow after flow deliverability test on a gas well, which is also called a four-point or back-pressure test.
These tests are run much like single-rate tests, except that the rate is changed by discrete amounts one or more times while the test continues. An example of this type of test is a flow after flow deliverability test on a gas well, which is also called a four-point or back-pressure test.
===When the tests are applicable===
===When the tests are applicable===
Flow tests can be useful when the reservoir is at uniform pressure, such as when a new well is completed or when a well has been shut in for a lengthy period. Flow tests are appropriate when a well must continue to produce revenue even though a test is needed. Analysis of flow tests is simplest when the rate is held strictly constant and in all cases requires known rates at all times during the test.
Flow tests can be useful when the reservoir is at uniform pressure, such as when a new well is completed or when a well has been shut in for a lengthy period. Flow tests are appropriate when a well must continue to produce revenue even though a test is needed. Analysis of flow tests is simplest when the rate is held strictly constant and in all cases requires known rates at all times during the test.
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===
<gallery mode = packed>
file:pressure-transient-testing_fig1.png|{{figure number|1}}Type curve that identifies the end of wellbore effects.
file:pressure-transient-testing_fig2.png|{{figure number|2}}(a) Derivative type curve used to match derivatives of test data. (b) Shapes of derivatives of test data for various reservoir conditions.
file:pressure-transient-testing_fig3.png|{{figure number|3}}Typical flow test data graph.
file:pressure-transient-testing_fig4.png|{{figure number|4}}Typical buildup test graph (Horner plot).
file:pressure-transient-testing_fig5.png|{{figure number|5}}(a) Typical buildup curve shape with flow barrier, (b) Doubling of slope on Horner plot for well near barrier.
</gallery>
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)]].
Similar equations are used for gas well test analysis.
Similar equations are used for gas well test analysis.
Extrapolation of pressure in a buildup test to Horner time ratio of unity provides an estimate of original reservoir pressure (new well) or “false” pressure, which serves as the basis for determining current drainage area pressure, <math>\bar{p}</math>, for a well with some pressure depletion in its drainage area caused by extended production of fluids. [[:file:pressure-transient-testing_fig4.png|Figure 4]] illustrates extrapolation of pressure to time ratio of unity.
Extrapolation of pressure in a buildup test to Horner time ratio of unity provides an estimate of original reservoir pressure (new well) or “false” pressure, which serves as the basis for determining current drainage area pressure, <math>\bar{p}</math>, for a well with some pressure depletion in its drainage area caused by extended production of fluids. [[:file:pressure-transient-testing_fig4.png|Figure 4]] illustrates extrapolation of pressure to time ratio of unity.