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''Formation testers'' are a class of wireline tools used to measure the downhole pressure of formations. Stationary measurements of formation pressure in an open hole are made at any number of depths during a single trip into the hole. These pressure measurements are useful in determining the following: (1) variations in pressure among various formations, (2) gradients of fluid pressure within a formation that can indicate fluid content, (3) gas-oil or water-oil contacts, and (4) local [[permeability]]. Comparison with initial reservoir pressures in development wells may indicate zonal pressure depletion. Formation testers are also used to retrieve samples containing fluids.

''Formation testers'' are a class of wireline tools used to measure the downhole pressure of formations. Stationary measurements of formation pressure in an open hole are made at any number of depths during a single trip into the hole. These pressure measurements are useful in determining

 

# variations in pressure among various formations,

# gradients of fluid pressure within a formation that can indicate fluid content,

# gas-oil or water-oil contacts, and  

# local [[permeability]].

 

Comparison with initial reservoir pressures in development wells may indicate zonal pressure depletion. Formation testers are also used to retrieve samples containing fluids.

==Operation of the tools==

==Operation of the tools==

==Formation permeability==

==Formation permeability==

Formation permeability has a significant effect on the drawdown response during a pretest. The pretest pressure recordings shown in Figure 5 illustrate typical records for sandstones at 0.1, 1, 10, and 100 md (millidarcys). While these figures are qualitative, quantitative techniques exist for estimating permeability using both the pressure drawdown and buildup characteristics of the pretest or sample test.

Formation permeability has a significant effect on the drawdown response during a pretest. The pretest pressure recordings shown in Figure 5 illustrate typical records for sandstones at 0.1, 1, 10, and 100 mD (millidarcys). While these figures are qualitative, quantitative techniques exist for estimating permeability using both the pressure drawdown and buildup characteristics of the pretest or sample test.

[[file:wireline-formation-testers_fig5.png|thumb|{{figure number|5}}Pretest pressure response to formation permeability as measured by a dual pretest tool. (From <ref name=pt04r18 />.)]]

[[file:wireline-formation-testers_fig5.png|thumb|{{figure number|5}}Pretest pressure response to formation permeability as measured by a dual pretest tool. (From <ref name=pt04r18 />.)]]

==See also==

==See also==

* [[Difficult lithologies]]

* [[Introduction to wireline methods]]

* [[Formation evaluation of naturally fractured reservoirs]]

* [[Basic open hole tools]]

* [[Basic open hole tools]]

* [[Basic tool table]]

* [[Basic tool table]]

* [[Introduction to wireline methods]]

* [[Formation evaluation of naturally fractured reservoirs]]

* [[Determination of water resistivity]]

* [[Standard interpretation]]

* [[Quick-look lithology from logs]]

* [[Quick-look lithology from logs]]

==References==

==References==