View source for Midale water saturation and pore geometry

{{publication 
 | image   = exploring-for-oil-and-gas-traps.png
 | width   = 120px
 | series  = Treatise in Petroleum Geology
 | title   = Exploring for Oil and Gas Traps
 | part    = Predicting the occurrence of oil and gas traps
 | chapter = Predicting reservoir system quality and performance
 | frompg  = 9-144
 | topg    = 9-144
 | author  = Dan J. Hartmann, Edward A. Beaumont
 | link    = http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm
 | pdf     = 
 | store   = http://store.aapg.org/detail.aspx?id=545
 | isbn    = 0-89181-602-X
}}
==Log response and S<sub>w</sub>==

Variations in pore geometry have the expected effect on log responses and [[water saturation]]s (S<sub>w</sub>). The Midale vuggy beds in a cored field well consist of interbeds of [[packstone]] and [[mudstone]]. [[:file:predicting-reservoir-system-quality-and-performance_fig9-103.png|Figure 1]] is a [[Pickett plot construction|Pickett plot]] for the Midale vuggy beds from an example well in Weyburn field. Data points cluster around higher [[Basic_open_hole_tools#Resistivity|resistivities]] for packstones (group A) and lower resistivities for mudstones (group B), reflecting the higher water saturations of the mudstones.

==Buckles plot==
<gallery mode=packed heights=200px widths=200x>
predicting-reservoir-system-quality-and-performance_fig9-103.png|{{figure number|1}}Pickett plot for the Midale vuggy beds from an example well in Weyburn field. Copyright: Coalson et al.;<ref name=Coalson1994>Coalson, E. B., S. M. Goolsby, and M. H. Franklin, 1994, Subtle seals and fluid-flow barriers in carbonate rocks, in J. C. Dolson, M. L. Hendricks, and W. A. Wescott, eds., Unconformity Related Hydrocarbons in Sedimentary Sequences: RMAG Guidebook for Petroleum Exploration and Exploitation in Clastic and Carbonate Sediments, p. 45–58.</ref> courtesy RMAG.
Predicting-reservoir-system-quality-and-performance fig9-102.png|{{figure number|2}}Illustration of (A) packstones that are  meso- to macroporous and (B) micro- to mesoporous mudstones. From Coalson et al.;<ref name=Coalson1994 /> courtesy RMAG.
predicting-reservoir-system-quality-and-performance_fig9-104.png|{{figure number|3}}Buckles plot for the Weyburn well. Copyright: Coalson et al.;<ref name=Coalson1994 /> courtesy RMAG.
</gallery>

As shown on [[:File:Predicting-reservoir-system-quality-and-performance fig9-102.png|Figure 2]], mudstones (B) are [[Wikipedia:Microporous material|micro]]- to [[Wikipedia:Mesoporous material|mesoporous]]; packstones (A) are meso- to [http://en.wiktionary.org/wiki/macroporous macroporous]. The mudstones have more pores with smaller pore throats than the packstones. This means mudstones have greater pore surface area and higher immobile S<sub>w</sub>. As a consequence, S<sub>w</sub> values for mudstones are higher at any given elevation in the oil column.

[[:file:predicting-reservoir-system-quality-and-performance_fig9-104.png|Figure 3]] is a [[Buckles plot]] for the Weyburn well. The hyperbolic curves represent equal values of S<sub>w</sub> × porosity (Φ). Points from the same pore type that fall along a hyperbolic curve are at immobile S<sub>w</sub>. Curves with higher values represent higher immobile S<sub>w</sub>.

On the plot, data for packstones (A), except for point 8, fall on a hyperbolic curve with a value between 100 and 300. This indicates these beds are at [http://petrowiki.org/Glossary%3AIrreducible_water_saturation immobile (irreducible) water saturations]. Point 8 is from a transition zone. Mudstones (B) also are at immobile water saturations but fall on a hyperbolic curve with higher numbers, between 1000 and 1300.

==See also==
* [[Evaluation of trap type]]
* [[Weyburn field location and trap problem]]
* [[Midale lithofacies and distribution]]
* [[Midale porosity, pore geometries, and petrophysics]]
* [[Weyburn seal capacity]]
* [[Midale seal capacity and trap type]]

==References==
{{reflist}}

==External links==
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* [http://archives.datapages.com/data/specpubs/beaumont/ch09/ch09.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]

[[Category:Predicting the occurrence of oil and gas traps]] 
[[Category:Predicting reservoir system quality and performance]]
[[Category:Treatise Handbook 3]]