Changes

==Multi-rate flow tests==

==Multi-rate flow tests==

[[file:pressure-transient-testing_fig1.png|left|thumb|{{figure number|1}}Type curve that identifies the end of wellbore effects.]]

[[file:pressure-transient-testing_fig1.png|thumb|{{figure number|1}}Type curve that identifies the end of wellbore effects.]]

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.

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.

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

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

===How the tests are analyzed===

===How the tests are analyzed===

Similar equations are used for gas well test analysis.

Similar equations are used for gas well test analysis.

[[file:pressure-transient-testing_fig5.png|left|thumb|{{figure number|5}}(a) Typical buildup curve shape with flow barrier, (b) Doubling of slope on Horner plot for well near barrier.]]

[[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.]]

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.