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Line 23: − + − [[file:wireline-formation-testers_fig1.png|left|thumb|{{figure number|1}}Wireline formation tester. (a) Retracted configuration (tool closed). (b) Set configuration (tool set).]]+ + + − − [[file:wireline-formation-testers_fig2.png|thumb|{{figure number|2}}Dual pretest formation tester sampling system. (From <ref name=pt04r18>Smolen, J., Litsey, L. R., 1979, Formation evaluation using wireline formation tester pressure data: Journal of Petroleum Technology, v. 31, n. 1, p. 25–32., 10., 2118/6822-PA</ref>.)]] − − [[file:wireline-formation-testers_fig3.png|left|thumb|{{figure number|3}}Pressure recording by a dual pretest formation tester. (From <ref name=pt04r18 />.)]]
→Operation of the tools
==Operation of the tools==
==Operation of the tools==
<gallery mode=packed heights=300px widths=300px>
wireline-formation-testers_fig1.png|{{figure number|1}}Wireline formation tester. (a) Retracted configuration (tool closed). (b) Set configuration (tool set).
wireline-formation-testers_fig2.png|{{figure number|2}}Dual pretest formation tester sampling system.<ref name=pt04r18>Smolen, J., Litsey, L. R., 1979, Formation evaluation using wireline formation tester pressure data: Journal of Petroleum Technology, v. 31, n. 1, p. 25–32., 10., 2118/6822-PA</ref>
</gallery>
When the tool is being moved downhole, the formation tester is in its retracted configuration. When a depth is selected for a pressure measurement, the formation tester is activated and hydraulically set or pressed against the formation. These conditions are shown schematically in [[:file:wireline-formation-testers_fig1.png|Figure 1]].
When the tool is being moved downhole, the formation tester is in its retracted configuration. When a depth is selected for a pressure measurement, the formation tester is activated and hydraulically set or pressed against the formation. These conditions are shown schematically in [[:file:wireline-formation-testers_fig1.png|Figure 1]].
Two modes of measurement exist: (1) a pretest measurement in which formation pressures are examined and (2) a fluid sample measurement in which formation fluids are physically withdrawn and retrieved to the surface for examination. The sequence of tool movements required to measure formation pressure begins when the formation tester is activated at a selected depth. The sampling system shown in [[:file:wireline-formation-testers_fig2.png|Figure 2]] illustrates how this measurement is made. Prior to activating the tool, the pressure gauge measures hydrostatic mud column pressure. Upon activation, the equalizing valve is shut and the packer and probe are pushed against the formation. The tool is now set. Within a few seconds, the pistons of the pretest chambers begin to withdraw, causing fluid from the formation to flow into the tool through the packer and probe assembly. The pretests are done sequentially with a small volume (typically 10 cc) of fluid drawn into chamber #1 over about 15 sec, followed by a similar volume flowing into chamber #2 at a higher flow rate. Upon completion of the pretests, a sample can be taken or the tool can be retracted. During retraction, the equalizing valve is opened and the pretest pistons expel the fluid taken in. The tool is now ready for the next test depth. Different vendors may use variations of this design that incorporate a single pretest chamber of fixed or variable volume.
Two modes of measurement exist: (1) a pretest measurement in which formation pressures are examined and (2) a fluid sample measurement in which formation fluids are physically withdrawn and retrieved to the surface for examination. The sequence of tool movements required to measure formation pressure begins when the formation tester is activated at a selected depth. The sampling system shown in [[:file:wireline-formation-testers_fig2.png|Figure 2]] illustrates how this measurement is made. Prior to activating the tool, the pressure gauge measures hydrostatic mud column pressure. Upon activation, the equalizing valve is shut and the packer and probe are pushed against the formation. The tool is now set. Within a few seconds, the pistons of the pretest chambers begin to withdraw, causing fluid from the formation to flow into the tool through the packer and probe assembly. The pretests are done sequentially with a small volume (typically 10 cc) of fluid drawn into chamber #1 over about 15 sec, followed by a similar volume flowing into chamber #2 at a higher flow rate. Upon completion of the pretests, a sample can be taken or the tool can be retracted. During retraction, the equalizing valve is opened and the pretest pistons expel the fluid taken in. The tool is now ready for the next test depth. Different vendors may use variations of this design that incorporate a single pretest chamber of fixed or variable volume.
==Pressure measurement==
==Pressure measurement==