Changes

During the pretest sequence, pressure is monitored with the tool sampling system. The schematic drawing in [[:file:wireline-formation-testers_fig3.png|Figure 3]] shows the pressure typically recorded during the pretest sequence. In this figure, time is shown as increasing to the right and pressure and flow rate are increasing upward. Initially, and when the tool is being set, the equalizing valve is open and the recorded pressure is hydrostatic mud column pressure. During the drawdown associated with the first pretest, the pressure is observed to drop, stabilize, and further decrease during the second pretest.

During the pretest sequence, pressure is monitored with the tool sampling system. The schematic drawing in [[:file:wireline-formation-testers_fig3.png|Figure 3]] shows the pressure typically recorded during the pretest sequence. In this figure, time is shown as increasing to the right and pressure and flow rate are increasing upward. Initially, and when the tool is being set, the equalizing valve is open and the recorded pressure is hydrostatic mud column pressure. During the drawdown associated with the first pretest, the pressure is observed to drop, stabilize, and further decrease during the second pretest.

When the second pretest is completed, the flow stops and the pressure builds up to formation pressure. [[:file:wireline-formation-testers_fig3.png|Figure 3]] illustrates the flow rates associated with the first and second pretests. Actual formation pressure can be taken when the pressure becomes stable or can be estimated from the character of the buildup if it has not yet stabilized when the tool is retracted.

When the second pretest is completed, the flow stops and the pressure builds up to formation pressure. [[:file:wireline-formation-testers_fig3.png|Figure 3]] illustrates the flow rates associated with the first and second pretests. Actual formation pressure can be taken when the pressure becomes stable or can be estimated from the character of the buildup if it has not yet stabilized when the tool is retracted.

[[file:wireline-formation-testers_fig4.png|thumb|{{figure number|4}}Typical log record of a single pretest formation tester showing both analog and digital log presentations. Copyright: Western Atlas International, 1987; courtesy of Atlas Wireline Services Division of Western Atlas International, Inc.]]

[[file:wireline-formation-testers_fig5.png|left|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_fig4.png|Figure 4]] is a typical log recorded by a formation tester that has a single pretest chamber. In the left log track, the solid curve represents the pressure detected by the gauge within the tool sampling system. Time is increasing downward along the log. The hydrostatic mud column, drawdown, and formation pressures are clearly detectable. The sudden increase at about 105 sec corresponds to the tool retraction and opening of the equalizing valve. On the right are four narrow tracks displaying the thousands, hundreds, tens, and units digit of the measured pressure. For example, after 80 sec, the formation pressure is 3927 psi. It is obvious on the units track that the pressure is increasing and actual formation pressure has not yet been reached.

[[:file:wireline-formation-testers_fig4.png|Figure 4]] is a typical log recorded by a formation tester that has a single pretest chamber. In the left log track, the solid curve represents the pressure detected by the gauge within the tool sampling system. Time is increasing downward along the log. The hydrostatic mud column, drawdown, and formation pressures are clearly detectable. The sudden increase at about 105 sec corresponds to the tool retraction and opening of the equalizing valve. On the right are four narrow tracks displaying the thousands, hundreds, tens, and units digit of the measured pressure. For example, after 80 sec, the formation pressure is 3927 psi. It is obvious on the units track that the pressure is increasing and actual formation pressure has not yet been reached.

==Formation permeability==

==Formation permeability==