Changes

===Pressure buildup tests===

===Pressure buildup tests===

In a pressure buildup test, one should stabilize the rate in the tested well for several days, that is, maintain the rate approximately constant. Then place a pressure measuring device as near the perforations as possible several hours before shut-in. Shut the well in and let the pressure build up. The rate at which pressure builds up with time reflects the formation properties. (For more details of pressure buildup and flow tests, see Matthews and Russell.<ref name=pt09r16>Matthews, C. S., Russell, D. G., 1967, Pressure buildup and flow tests in wells: Dallas, TX, Society of Petroleum Engineers Monograph Series No. 1, 172 p.</ref>)

In a pressure buildup test, one should stabilize the rate in the tested well for several days, that is, maintain the rate approximately constant. Then place a pressure measuring device as near the perforations as possible several hours before shut-in. Shut the well in and let the pressure build up. The rate at which pressure builds up with time reflects the formation properties. (For more details of pressure buildup and flow tests, see Matthews and Russell.<ref name=pt09r16>Matthews, C. S., and D. G. Russell, 1967, Pressure buildup and flow tests in wells: Dallas, TX, Society of Petroleum Engineers Monograph Series No. 1, 172 p.</ref>)

==Multi-rate flow tests==

==Multi-rate flow tests==

===How the tests are analyzed===

===How the tests are analyzed===

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

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_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.

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:

* Δ''p''_lhr = pressure change in first hour of test (psi)

* Δ''p''_lhr = pressure change in first hour of test (psi)

* ''ϕ'' = [[porosity]] (fraction)

* ''ϕ'' = [[porosity]] (fraction)

* ''μ'' = viscosity (cp)

* ''μ'' = [[viscosity]] (cp)

* ''c''_t = total compressibility of formation and its fluids (psi^–1)

* ''c''_t = total compressibility of formation and its fluids (psi^–1)

* ''r''_w = wellbore radius or hole size (ft)

* ''r''_w = wellbore radius or hole size (ft)

==Long-term production tests==

==Long-term production tests==

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file:pressure-transient-testing_fig6.png|{{figure number|6}}Fetkovich's type curve for analyzing long-term production data. After Fetkovich.<ref name=pt09r8>Fetkovich, M. J., 1980, Decline curve analysis using type curves: Journal of Petroleum Technology, June, p. 1065–1077.</ref>

file:pressure-transient-testing_fig6.png|{{figure number|6}}Fetkovich's type curve for analyzing long-term production data. After Fetkovich.<ref name=pt09r8>Fetkovich, M. J., 1980, Decline curve analysis using type curves: Journal of Petroleum Technology, June, p. 1065–1077.</ref>

file:pressure-transient-testing_fig7.png|{{figure number|7}}Actual production data matched on a Fetkovich type curve.

file:pressure-transient-testing_fig7.png|{{figure number|7}}Actual production data matched on a Fetkovich type curve.

More complex tests, with abrupt changes in rate and BHP, are more readily analyzed with computer reservoir simulators. These simulators are used to history-match production data to obtain a reservoir description, which is then used to obtain a long-term production forecast and thus to estimate reserves. [[:file:pressure-transient-testing_fig8.png|Figure 8]] shows an example of a history match of production data and a forecast of future performance of the well using the reservoir description obtained from the history match.

More complex tests, with abrupt changes in rate and BHP, are more readily analyzed with computer reservoir simulators. These simulators are used to history-match production data to obtain a reservoir description, which is then used to obtain a long-term production forecast and thus to estimate reserves. [[:file:pressure-transient-testing_fig8.png|Figure 8]] shows an example of a history match of production data and a forecast of future performance of the well using the reservoir description obtained from the history match.

==Interference and pulse tests==

==Interference and pulse tests==

[[file:pressure-transient-testing_fig10.png|thumb|{{figure number|10}}Schematic illustration of rate history and pressure response for an interference test. (After <ref name=pt09r7 />.)]]

[[file:pressure-transient-testing_fig9.png|thumb|300px|{{figure number|9}}Active and observation wells in an interference pulse test.<ref name=pt09r7>Earlougher, R. C., Jr., 1977, Advances in Well Test Analysis: Dallas, TX, American Institute of Mining, Metallurgical and Petroleum Engineers, Society of Petroleum Engineer's Monograph 5, 264 p.</ref>]]

Interference and pulse tests are run to obtain the following information:

Interference and pulse tests are run to obtain the following information:

* Average porosities in the areas influenced by the tests

* Average porosities in the areas influenced by the tests

[[file:pressure-transient-testing_fig11.png|left|thumb|{{figure number|11}}Schematic Illustration of rate (pulse) history and pressure response for a pulse test.<ref name=pt09r7 />]]

===How the tests are run===

===How the tests are run===

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file:pressure-transient-testing_fig10.png|{{figure number|10}}Schematic illustration of rate history and pressure response for an interference test. (After <ref name=pt09r7 />.)

file:pressure-transient-testing_fig11.png|{{figure number|11}}Schematic Illustration of rate (pulse) history and pressure response for a pulse test.<ref name=pt09r7 />

Interference tests are run by first shutting in the portion of the reservoir in the area affected by the test. Then one produces (or injects into) one well (called the active well) and measures the pressure response in the offset wells. [[:file:pressure-transient-testing_fig9.png|Figure 9]] shows a typical interference test pattern, and [[:file:pressure-transient-testing_fig10.png|Figure 10]] is a plot of a typical response in an observation well.

Interference tests are run by first shutting in the portion of the reservoir in the area affected by the test. Then one produces (or injects into) one well (called the active well) and measures the pressure response in the [[offset]] wells. [[:file:pressure-transient-testing_fig9.png|Figure 9]] shows a typical interference test pattern, and [[:file:pressure-transient-testing_fig10.png|Figure 10]] is a plot of a typical response in an observation well.

Pulse tests are performed by first producing (or injecting into) the active well for a few hours. The active well is then shut-in, then returned to production, shut-in again, and so on in a regular, repeating pattern. The response in the offset wells is then measured while continuing to produce all wells in the field except those directly involved in the test. This is possible because the “noise” caused by continued production of wells not directly involved in the test can be filtered out using the response caused by the repeated on-off pattern in the active well. [[:file:pressure-transient-testing_fig11.png|Figure 11]] shows a typical response in a pulse test observation well.

Pulse tests are performed by first producing (or injecting into) the active well for a few hours. The active well is then shut-in, then returned to production, shut-in again, and so on in a regular, repeating pattern. The response in the offset wells is then measured while continuing to produce all wells in the field except those directly involved in the test. This is possible because the “noise” caused by continued production of wells not directly involved in the test can be filtered out using the response caused by the repeated on-off pattern in the active well. [[:file:pressure-transient-testing_fig11.png|Figure 11]] shows a typical response in a pulse test observation well.

[[Category:Production engineering methods]]

[[Category:Production engineering methods]]