Difference between revisions of "Free water level determination using pressure"

	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

Latest revision as of 17:54, 17 February 2022

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]

Figure 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. 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 (P_b ) at the depth of the measured pressure (P_m ) from the measured pressure:
- $P_{\rm {b}}=P_{\rm {m}}-P_{\rm {hydrostatic}}$
Determine buoyancy pressure gradient (P_bg ):
- $P_{\rm {bg}}=P_{\rm {hydrostatic\ pressure\ gradient}}-P_{\rm {hydrocarbon\ pressure\ gradient}}$
Calculate downdip length of hydrocarbon column (h):
- $h={\frac {P_{\rm {b}}}{P_{\rm {bg}}}}$

As an example, let's determine the downdip length of a 30°API oil column with the following givens:

P_m = pressure::3555 psi at depth::7611 ft
P_hydrostatic = 3525 psi
P_{hydrostatic pressure gradient} = 0.465 psi/ft
P_{hydrocarbon pressure gradient} = 0.38 psi/ft

Answer (tied back to steps above):

P_{\rm {b}}=P_{m}-P_{\rm {hydrostatic}}=3555-3525=30\ \mathrm {psi}

P_{\rm {hydrostatic\ pressure\ gradient}}-P_{\rm {hydrocarbon\ pressure\ gradient}}=0.465-0.38=0.085{\mbox{ psi/ft}}

h={\frac {P_{\rm {b}}}{P_{\rm {bg}}}}=30{\mbox{ psi}}\div 0.054{\mbox{ psi/ft}}=556{\mbox{ ft}}

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

External links[edit]

find literature about
Free water level determination using pressure

@@ Line 6: / Line 6: @@
   | part    = Critical elements of the petroleum system
   | 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
   | link    = http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm
@@ Line 19: / Line 19: @@
 [[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==
-The table 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.
+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.
-{| class = "wikitable"
+# 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>
-! Step
+# Determine buoyancy pressure gradient (''P''<sub>bg</sub> ):
-! Action
+#*:<math>P_{\rm bg} = P_{\rm hydrostatic\ pressure\ gradient} - P_{\rm hydrocarbon\ pressure\ gradient}</math>
-|-
+# Calculate downdip length of [[hydrocarbon column]] (''h''):
-| 1
+#*:<math>h = \frac{P_{\rm b}}{P_{\rm bg}}</math>
-| 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>
-|-
-| 2
-| Determine buoyancy pressure gradient (''P''<sub>bg</sub> ):
-:<math>P_{\rm bg} = P_{\rm hydrostatic\ pressure\ gradient} - P_{\rm hydrocarbon\ pressure\ gradient}</math>
-|-
-| 3
-| 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:
@@ Line 78: / Line 61: @@
 [[Category:Critical elements of the petroleum system]]
 [[Category:Formation fluid pressure and its application]]
+[[Category:Treatise Handbook 3]]

Difference between revisions of "Free water level determination using pressure"

Latest revision as of 17:54, 17 February 2022

Contents

Procedure: using repeat formation tester (RFT) data[edit]

Procedure using a single measurement[edit]

See also[edit]

External links[edit]

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