Changes

  | 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  = 5-1

  | frompg  = 5-27

  | topg    = 5-64

  | 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

  | isbn    = 0-89181-602-X

  | isbn    = 0-89181-602-X

}}

}}

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.

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-water level (FWL) is projecting 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.

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 table below outlines the procedure for determining the free-water level using a single pressure buildup point in the reservoir.

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''_b ) at the depth of the measured pressure (P_m ) from the measured pressure:

#*:<math>P_{\rm b} = P_{\rm m} - P_{\rm hydrostatic}</math>

# Determine buoyancy pressure gradient (''P''_bg ):

#*:<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>

| Determine buoyancy pressure (''P''_b ) at the depth of the measured pressure (P_m ) from the measured pressure:

 

:<math>P_{\rm b} = P_{\rm m} - P_{\rm hydrostatic}</math>

 

| Determine buoyancy pressure gradient (''P''_bg ):

 

:<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>

 

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:

:<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-water level is at [[depth::8167 ft]].

Therefore, the free water level is at [[depth::8167 ft]].

==See also==

==See also==

[[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]]