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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: |
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− | :<math>\mbox{P}_{\rm b} = \mbox{P}_{\rm m} - \mbox{P}_{\rm hydrostatic}</math> | + | :<math>P_{\rm b} = P_{\rm m} - P_{\rm hydrostatic}</math> |
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− | | Determine buoyancy pressure gradient (P<sub>bg</sub> ): | + | | Determine buoyancy pressure gradient (''P''<sub>bg</sub> ): |
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− | :<math>\mbox{P}_{\rm bg} = \mbox{P}_{\rm hydrostatic\ pressure\ gradient} - \mbox{P}_{\rm hydrocarbon\ pressure\ gradient}</math> | + | :<math>P_{\rm bg} = P_{\rm hydrostatic\ pressure\ gradient} - P_{\rm hydrocarbon\ pressure\ gradient}</math> |
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− | | Calculate downdip length of hydrocarbon column (h): | + | | Calculate downdip length of hydrocarbon column (''h''): |
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− | :<math>\mbox{h} = \frac{\mbox{P}_{\rm b}}{\mbox{P}_{\rm bg}}</math> | + | :<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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− | * P<sub>m</sub> = 3555 psi at 7611 ft | + | * ''P''<sub>m</sub> = [[pressure::3555 psi]] at [[depth::7611 ft]] |
− | * P<sub>hydrostatic</sub> = 3525 psi | + | * ''P''<sub>hydrostatic</sub> = 3525 psi |
− | * P<sub>hydrostatic pressure gradient</sub> = 0.465 psi/ft | + | * ''P''<sub>hydrostatic pressure gradient</sub> = 0.465 psi/ft |
− | * P<sub>hydrocarbon pressure gradient</sub> = 0.38 psi/ft | + | * ''P''<sub>hydrocarbon pressure gradient</sub> = 0.38 psi/ft |
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| '''Answer''' (tied back to steps above): | | '''Answer''' (tied back to steps above): |
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− | Step 1:
| + | :<math>P_{\rm b} = P_{m} - P_{\rm hydrostatic} = 3555 - 3525 = 30\ \mathrm{psi}</math> |
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− | :<math>\mbox{P}_{\rm b} = \mbox{P}_{m} - \mbox{P}_{\rm hydrostatic} = 3555 - 3525 = 30 psi</math> | + | :<math>P_{\rm hydrostatic\ pressure\ gradient} - P_{\rm hydrocarbon\ pressure\ gradient} = 0.465 - 0.38 = 0.085 \mbox{ psi/ft}</math> |
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− | Step 2:
| + | :<math>h = \frac{P_{\rm b}}{P_{\rm bg}} = 30 \mbox{ psi} \div 0.054 \mbox{ psi/ft} = 556 \mbox{ ft}</math> |
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− | :<math>\mbox{P}_{\rm hydrostatic\ pressure\ gradient} - \mbox{P}_{\rm hydrocarbon\ pressure\ gradient} = 0.465 - 0.38 = 0.085 \mbox{ psi/ft}</math>
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− | Step 3:
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− | :<math>\mbox{h} = \frac{\mbox{P}_{\rm b}}{\mbox{P}_{\rm bg}} = \mbox{30 \mbox{ psi}}{0.054 \mbox{ psi/ft}} = 556 \mbox{ ft}</math> | |
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| Therefore, the free-water level is at [[depth::8167 ft]]. | | Therefore, the free-water level is at [[depth::8167 ft]]. |