Difference between revisions of "Free water level determination using pressure"
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− | | Determine buoyancy pressure (''P''<sub>b</sub> ) at the depth of the measured pressure (P<sub>m</sub> ) from the measured pressure: | + | | 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> | :<math>P_{\rm b} = P_{\rm m} - P_{\rm hydrostatic}</math> | ||
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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== |
Revision as of 14:32, 28 July 2014
Exploring for Oil and Gas Traps | |
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Series | Treatise in Petroleum Geology |
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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 table below outlines the procedure for determining the free water level using a single pressure buildup point in the reservoir.
Step | Action |
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1 | Determine buoyancy pressure (Pb ) at the depth of the measured pressure (Pm ) from the measured pressure:
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2 | Determine buoyancy pressure gradient (Pbg ):
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3 | Calculate downdip length of hydrocarbon column (h):
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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