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|thumb|{{figure number|1}}See text for explanation.]]
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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==
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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|{{figure number|2}}See text for explanation.]]
 
  
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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:
  
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* 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.
−
[[file:predicting-reservoir-system-quality-and-performance_fig9-42.png|thumb|{{figure number|3}}See text for explanation.]]
 
−
 
 
−
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==
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* [[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

Exploring for Oil and Gas Traps
Series Treatise in Petroleum Geology
Part Predicting the occurrence of oil and gas traps
Chapter Predicting reservoir system quality and performance
Author Dan J. Hartmann, Edward A. Beaumont
Link Web page
Store AAPG Store

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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