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Line 50: + + + + − − [[file:wireline-formation-testers_fig7.png|thumb|left|{{figure number|7}}Pressure contour map in zone of water injection. Copyright: Western Atlas International, 1987; courtesy of Atlas Wireline Services Division of Western Atlas International, Inc.]]
→Pressure applications
==Pressure applications==
==Pressure applications==
<gallery mode=packed heights=200px widths=200px>
wireline-formation-testers_fig6.png|{{figure number|6}}Pretest pressure response measurements across a reservoir. Copyright: Schlumberger Well Services, 1981.
wireline-formation-testers_fig7.png|{{figure number|7}}Pressure contour map in zone of water injection. Copyright: Western Atlas International, 1987; courtesy of Atlas Wireline Services Division of Western Atlas International, Inc.
</gallery>
Although formation testers can take samples, they are often run solely for the pressure information available from the pretest. [[:file:wireline-formation-testers_fig6.png|Figure 6]] shows how such pretest data can be useful. In this figure, the well is shown penetrating a reservoir that has gas, oil, and water intervals. The formation tester is set at numerous depth intervals across this reservoir. The formation pressure recorded by the tool is indicated by an “x,” while the hydrostatic mud column pressure is indicated by an “o.” The degree of overbalance (that is, the difference between the mud and formation pressures) is clearly visible from the schematic. The fluid gradients are also detectable, and the gas column is readily distinguished from the oil, which is also distinguishable from the water. The location of the gas-oil and water-oil contacts can also be determined from the formation pressure profile.
Although formation testers can take samples, they are often run solely for the pressure information available from the pretest. [[:file:wireline-formation-testers_fig6.png|Figure 6]] shows how such pretest data can be useful. In this figure, the well is shown penetrating a reservoir that has gas, oil, and water intervals. The formation tester is set at numerous depth intervals across this reservoir. The formation pressure recorded by the tool is indicated by an “x,” while the hydrostatic mud column pressure is indicated by an “o.” The degree of overbalance (that is, the difference between the mud and formation pressures) is clearly visible from the schematic. The fluid gradients are also detectable, and the gas column is readily distinguished from the oil, which is also distinguishable from the water. The location of the gas-oil and water-oil contacts can also be determined from the formation pressure profile.
After a reservoir has been produced, some pressure decline can be expected. Formation testers are frequently run in development or in-fill wells. When compared to initial reservoir pressures, pressure profiles in these wells often show that certain zones may have produced more than neighboring zones, thereby indicating the presence of permeability barriers.
After a reservoir has been produced, some pressure decline can be expected. Formation testers are frequently run in development or in-fill wells. When compared to initial reservoir pressures, pressure profiles in these wells often show that certain zones may have produced more than neighboring zones, thereby indicating the presence of permeability barriers.