Difference between revisions of "Water saturation distribution in a reservoir"
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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. | 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. | ||
− | + | <gallery mode=packed heights=200px widths=200px> | |
+ | 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> | ||
==BVW== | ==BVW== | ||
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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. | 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. | ||
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==S<sub>w</sub>—depth plots== | ==S<sub>w</sub>—depth plots== | ||
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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 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: | ||
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==Height–s<sub>w</sub>–pore type diagram== | ==Height–s<sub>w</sub>–pore type diagram== | ||
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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, saltwater formation water, and water wet. | 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, saltwater formation water, and water wet. | ||
Revision as of 19:25, 25 September 2014
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 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]
Bulk volume water (BVW) equals 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]
Sw–depth plots are simple plots of Sw vs. depth. They 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:
- Transition and waste zones
- Flow units
- Containers
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, saltwater formation water, and water wet.