Difference between revisions of "Free water level determination using pressure"
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| part = Critical elements of the petroleum system | | part = Critical elements of the petroleum system | ||
| chapter = Formation fluid pressure and its application | | chapter = Formation fluid pressure and its application | ||
− | | frompg = 5- | + | | frompg = 5-27 |
− | | topg = 5- | + | | topg = 5-28 |
| author = Edward A. Beaumont, Forrest Fiedler | | author = Edward A. Beaumont, Forrest Fiedler | ||
| link = http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm | | link = http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm | ||
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| isbn = 0-89181-602-X | | isbn = 0-89181-602-X | ||
}} | }} | ||
− | The free | + | The [[free water level]] occurs where [[buoyancy pressure]] is zero in the reservoir-aquifer system. It defines the down[[dip]] limits of an [[accumulation]]. Pressure data reliability affects the resolution; however, resolution improves when it is supplemented with other petrophysical information. |
− | ==Procedure: using RFT data== | + | ==Procedure: using repeat formation tester (RFT) data== |
[[file:formation-fluid-pressure-and-its-application_fig5-12.png|400px|thumb|{{figure number|1}}Easy method for determining free-water level (FWL) by projecting RFT pressure data downward from a reservoir to the aquifer.]] | [[file:formation-fluid-pressure-and-its-application_fig5-12.png|400px|thumb|{{figure number|1}}Easy method for determining free-water level (FWL) by projecting RFT pressure data downward from a reservoir to the aquifer.]] | ||
− | An easy method for determining free | + | An easy method for determining free water level (FWL) is projecting [[Wireline formation testers|RFT]] pressure data downward from a reservoir to the aquifer. [[:file:formation-fluid-pressure-and-its-application_fig5-12.png|Figure 1]] illustrates the procedure. |
==Procedure using a single measurement== | ==Procedure using a single measurement== | ||
− | The | + | The list below outlines the procedure for determining the free water level using a single [[Pressure_transient_testing#Pressure_drawdown_and_buildup_tests|pressure buildup]] point in the reservoir. |
− | + | # Determine [[buoyancy pressure]] (''P''<sub>b</sub> ) at the depth of the measured pressure (P<sub>m</sub> ) from the measured pressure: | |
− | + | #*:<math>P_{\rm b} = P_{\rm m} - P_{\rm hydrostatic}</math> | |
− | + | # Determine buoyancy pressure gradient (''P''<sub>bg</sub> ): | |
− | + | #*:<math>P_{\rm bg} = P_{\rm hydrostatic\ pressure\ gradient} - P_{\rm hydrocarbon\ pressure\ gradient}</math> | |
− | + | # Calculate downdip length of [[hydrocarbon column]] (''h''): | |
− | + | #*:<math>h = \frac{P_{\rm b}}{P_{\rm bg}}</math> | |
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− | :<math>P_{\rm b} = P_{\rm m} - P_{\rm hydrostatic}</math> | ||
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− | :<math>P_{\rm bg} = P_{\rm hydrostatic\ pressure\ gradient} - P_{\rm hydrocarbon\ pressure\ gradient}</math> | ||
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− | :<math>h = \frac{P_{\rm b}}{P_{\rm bg}}</math> | ||
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As an example, let's determine the downdip length of a 30°API oil column with the following givens: | As an example, let's determine the downdip length of a 30°API oil column with the following givens: | ||
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:<math>h = \frac{P_{\rm b}}{P_{\rm bg}} = 30 \mbox{ psi} \div 0.054 \mbox{ psi/ft} = 556 \mbox{ ft}</math> | :<math>h = \frac{P_{\rm b}}{P_{\rm bg}} = 30 \mbox{ psi} \div 0.054 \mbox{ psi/ft} = 556 \mbox{ ft}</math> | ||
− | Therefore, the free | + | Therefore, the free water level is at [[depth::8167 ft]]. |
==See also== | ==See also== | ||
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[[Category:Critical elements of the petroleum system]] | [[Category:Critical elements of the petroleum system]] | ||
[[Category:Formation fluid pressure and its application]] | [[Category:Formation fluid pressure and its application]] | ||
+ | [[Category:Treatise Handbook 3]] |
Latest revision as of 17:54, 17 February 2022
Exploring for Oil and Gas Traps | |
Series | Treatise in Petroleum Geology |
---|---|
Part | Critical elements of the petroleum system |
Chapter | Formation fluid pressure and its application |
Author | Edward A. Beaumont, Forrest Fiedler |
Link | Web page |
Store | AAPG Store |
The free water level occurs where buoyancy pressure is zero in the reservoir-aquifer system. It defines the downdip limits of an accumulation. Pressure data reliability affects the resolution; however, resolution improves when it is supplemented with other petrophysical information.
Procedure: using repeat formation tester (RFT) data[edit]
An easy method for determining free water level (FWL) is projecting RFT pressure data downward from a reservoir to the aquifer. Figure 1 illustrates the procedure.
Procedure using a single measurement[edit]
The list below outlines the procedure for determining the free water level using a single pressure buildup point in the reservoir.
- Determine buoyancy pressure (Pb ) at the depth of the measured pressure (Pm ) from the measured pressure:
- Determine buoyancy pressure gradient (Pbg ):
- Calculate downdip length of hydrocarbon column (h):
As an example, let's determine the downdip length of a 30°API oil column with the following givens:
- Pm = pressure::3555 psi at depth::7611 ft
- Phydrostatic = 3525 psi
- Phydrostatic pressure gradient = 0.465 psi/ft
- Phydrocarbon pressure gradient = 0.38 psi/ft
Answer (tied back to steps above):
Therefore, the free water level is at depth::8167 ft.
See also[edit]
- Static hydrocarbon pressure gradients
- Estimating static oil pressure gradients
- Estimating static gas pressure gradients
- Plotting the hydrocarbon pressure gradient