Difference between revisions of "Water saturation distribution in a reservoir"

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  | part    = Predicting the occurrence of oil and gas traps
 
  | part    = Predicting the occurrence of oil and gas traps
 
  | chapter = Predicting reservoir system quality and performance
 
  | chapter = Predicting reservoir system quality and performance
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  | frompg  = 9-1
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  | frompg  = 9-65
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  | topg    = 9-156
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  | topg    = 9-67
 
  | author  = Dan J. Hartmann, Edward A. Beaumont
 
  | author  = Dan J. Hartmann, Edward A. Beaumont
 
  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm
 
  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm
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  | isbn    = 0-89181-602-X
 
  | isbn    = 0-89181-602-X
 
}}
 
}}
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The distribution of water saturation values within a reservoir depends on the height above free water, hydrocarbon type, pore throat-size distribution, and pore geometry. Mapping S<sub>w</sub> distribution in a reservoir helps us predict trap boundaries.
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The distribution of [[water saturation]] (S<sub>w</sub>) values within a [[reservoir]] depends on the height above [[Free water level|free water]], [[hydrocarbon]] type, [[Pore throat size and connectivity|pore throat-size distribution]], and [[Reservoir quality|pore geometry]]. Mapping S<sub>w</sub> distribution in a reservoir helps us predict trap boundaries.
  
 
==BVW==
 
==BVW==
 +
<gallery mode=packed heights=250px widths=205px>
 +
file:predicting-reservoir-system-quality-and-performance_fig9-40.png|{{figure number|1}}How a [[Buckles plot]] relates to capillary pressure, fluid distribution, and fluid recovery in a reservoir.
 +
file:predicting-reservoir-system-quality-and-performance_fig9-41.png|{{figure number|2}}Hypothetical example of an S<sub>w</sub>–depth plot with estimated S<sub>w</sub> distribution curves for several flow units for a hydrocarbon-bearing zone in a well.
 +
file:predicting-reservoir-system-quality-and-performance_fig9-42.png|{{figure number|3}}Empirical ternary diagram for estimating height above free water, pore type (r<sub>35</sub>), and S<sub>w</sub> for a flow unit when the other two variables are known.
 +
</gallery>
  
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[[file:predicting-reservoir-system-quality-and-performance_fig9-40.png|300px|thumb|{{figure number|1}}How a Buckles plot relates to capillary pressure, fluid distribution, and fluid recovery in a reservoir.]]
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Bulk volume water (BVW) equals [[porosity]] (Φ) × S<sub>w</sub>. In zones with the same pore type and geometry, BVW is a function of the height above the [[free water level]]. Above the transition zone, BVW is fairly constant. Below the transition zone, BVW is variable.
  
−
Bulk volume water (BVW) equals Φ × S<sub>w</sub>. In zones with the same pore type and geometry, BVW is a function of the height above the [[free water level]]. Above the transition zone, BVW is fairly constant. Below the transition zone, BVW is variable.
+
A [[Buckles plot]] is a plot of S<sub>w</sub> vs. porosity. Contours of equal BVW are drawn on the plot.
−
 
 
−
A [[Buckles plot]] is a plot of S<sub>w</sub> vs. [[porosity]]. Contours of equal BVW are drawn on the plot.
 
  
 
* Points plot on a hyperbolic BVW line where the formation is near immobile water if the points come from a reservoir with consistent pore type and pore geometry.
 
* Points plot on a hyperbolic BVW line where the formation is near immobile water if the points come from a reservoir with consistent pore type and pore geometry.
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==Limitations of BVW==
 
==Limitations of BVW==
−
BVW and Buckles plots can be confusing in interbedded lithologies or in areas where facies changes occur because of changing pore types.
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BVW and Buckles plots can be confusing in interbedded lithologies or in areas where [[Lithofacies|facies]] changes occur because of changing pore types.
−
 
 
−
==S<sub>w</sub>—depth plots==
 
−
[[file:predicting-reservoir-system-quality-and-performance_fig9-41.png|thumb|300px|{{figure number|2}}Hypothetical example of an S<sub>w</sub>–depth plot with estimated S<sub>w</sub> distribution curves for several flow units for a hydrocarbon-bearing zone in a well.]]
 
  
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S<sub>w</sub>–depth plots are simple plots of S<sub>w</sub> vs. depth. They illustrate how S<sub>w</sub> varies within a hydrocarbon-bearing zone. Variations reflect different pore types and/or height above free water. An S<sub>w</sub>–depth plot can be used to delineate three things:
+
==S<sub>w</sub>–depth plots==
 +
These illustrate how S<sub>w</sub> varies within a hydrocarbon-bearing zone. Variations reflect different [[Reservoir quality|pore types]] and/or height above [[Free water level|free water]]. An S<sub>w</sub>–depth plot can be used to delineate three things:
  
−
* Transition and waste zones
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* [[What_is_a_reservoir_system%3F#Waste_and_transition_zones|Transition and waste zones]]
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* Flow units
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* [[Flow units for reservoir characterization|Flow units]]
 
* Containers
 
* Containers
  
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Individual plots can be prepared for wells along dip and strike and correlated to show S<sub>w</sub> changes across a reservoir or field. [[:file:predicting-reservoir-system-quality-and-performance_fig9-41.png|Figure 2]] is a hypothetical example of an S<sub>w</sub>–depth plot with estimated S<sub>w</sub> distribution curves for several flow units for a hydrocarbon-bearing zone in a well.
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Individual plots can be prepared for wells along [[dip]] and [[strike]] and correlated to show S<sub>w</sub> changes across a reservoir or field. [[:file:predicting-reservoir-system-quality-and-performance_fig9-41.png|Figure 2]] is a hypothetical example of an S<sub>w</sub>–depth plot with estimated S<sub>w</sub> distribution curves for several flow units for a hydrocarbon-bearing zone in a well.
  
 
==Height–s<sub>w</sub>–pore type diagram==
 
==Height–s<sub>w</sub>–pore type diagram==
−
 
+
The empirical ternary diagram in [[:file:predicting-reservoir-system-quality-and-performance_fig9-42.png|Figure 3]] is handy for estimating either height above free water, pore type ([[Characterizing_rock_quality#What_is_r35.3F|r<sub>35</sub>]]), or S<sub>w</sub> for a flow unit when the other two variables are known. For example, if S<sub>w</sub> for a flow unit is 20% and the pore type is macro with a port size of approximately 3μ, then the height above free water for the flow unit is approximately [[length::100 ft]]. Assumptions for the diagram include 30°API [[gravity]] oil, saline formation water, and a water-wet reservoir.
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[[file:predicting-reservoir-system-quality-and-performance_fig9-42.png|300px|thumb|{{figure number|3}}Empirical ternary diagram for estimating height above free water, pore type (r<sub>35</sub>), and S<sub>w</sub> for a flow unit when the other two variables are known.]]
 
−
 
 
−
The empirical ternary diagram in [[:file:predicting-reservoir-system-quality-and-performance_fig9-42.png|Figure 3]] is handy for estimating either height above free water, pore type (r<sub>35</sub>), or S<sub>w</sub> for a flow unit when the other two variables are known. For example, if S<sub>w</sub> for a flow unit is 20% and the pore type is macro with a port size of approximately 3μ, then the height above free water for the flow unit is approximately [[length::100 ft]]. Assumptions for the diagram include 30°API gravity oil, saltwater formation water, and water wet.
 
  
 
==See also==
 
==See also==
−
* [[Interpreting water saturation]]
 
 
* [[Interpreting hydrocarbon shows]]
 
* [[Interpreting hydrocarbon shows]]
 
* [[Predicting hydrocarbon recovery]]
 
* [[Predicting hydrocarbon recovery]]
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[[Category:Predicting the occurrence of oil and gas traps]]  
 
[[Category:Predicting the occurrence of oil and gas traps]]  
 
[[Category:Predicting reservoir system quality and performance]]
 
[[Category:Predicting reservoir system quality and performance]]
 +
[[Category:Treatise Handbook 3]]

Latest revision as of 17:09, 5 April 2022

The distribution of water saturation (Sw) values within a reservoir depends on the height above free water, hydrocarbon type, pore throat-size distribution, and pore geometry. Mapping Sw distribution in a reservoir helps us predict trap boundaries.

BVW[edit]

  • Figure 1 How a Buckles plot relates to capillary pressure, fluid distribution, and fluid recovery in a reservoir.

  • Figure 2 Hypothetical example of an Sw–depth plot with estimated Sw distribution curves for several flow units for a hydrocarbon-bearing zone in a well.

  • Figure 3 Empirical ternary diagram for estimating height above free water, pore type (r35), and Sw for a flow unit when the other two variables are known.

Bulk volume water (BVW) equals porosity (Φ) × Sw. In zones with the same pore type and geometry, BVW is a function of the height above the free water level. Above the transition zone, BVW is fairly constant. Below the transition zone, BVW is variable.

A Buckles plot is a plot of Sw vs. porosity. Contours of equal BVW are drawn on the plot.

  • Points plot on a hyperbolic BVW line where the formation is near immobile water if the points come from a reservoir with consistent pore type and pore geometry.
  • Points scatter on a Buckles plot where the formation falls below the top of the transition zone.

Figure 1 shows how a Buckles plot relates to capillary pressure, fluid distribution, and fluid recovery in a reservoir.

Limitations of BVW[edit]

BVW and Buckles plots can be confusing in interbedded lithologies or in areas where facies changes occur because of changing pore types.

Sw–depth plots[edit]

These illustrate how Sw varies within a hydrocarbon-bearing zone. Variations reflect different pore types and/or height above free water. An Sw–depth plot can be used to delineate three things:

Individual plots can be prepared for wells along dip and strike and correlated to show Sw changes across a reservoir or field. Figure 2 is a hypothetical example of an Sw–depth plot with estimated Sw distribution curves for several flow units for a hydrocarbon-bearing zone in a well.

Height–sw–pore type diagram[edit]

The empirical ternary diagram in Figure 3 is handy for estimating either height above free water, pore type (r35), or Sw for a flow unit when the other two variables are known. For example, if Sw for a flow unit is 20% and the pore type is macro with a port size of approximately 3μ, then the height above free water for the flow unit is approximately length::100 ft. Assumptions for the diagram include 30°API gravity oil, saline formation water, and a water-wet reservoir.

See also[edit]

External links[edit]

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