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Publication History:
This article is based on
Chapter 8 of "The Log Analysis Handbook" by E. R. Crain, P.Eng., published by Pennwell Books 1986 Updated 2004,
2020.
This
webpage version is the copyrighted intellectual
property of the author.
Do not copy or distribute in any form without explicit
permission. |
Selection of WATER SATURATION MethodS
The answers for all the water
saturation solutions will vary, and in some
cases will be unreasonable or impossible to calculate due to lack of
data. In order of preference, we would choose:
BEST MODEL -- Use whenever possible
1. Simandoux Model, reverts to Archie Model when Vsh
= 0. Cznnot create negative saturation answers.
OTHWER SATURATION MODELS --- Use only within
limitations
2. Archie Model. Best use is in clean sands or
carbonates. Use Simandoux to handle both clean and shaly
rocks.
3. Dual Water Model, reverts to Archie Model when Vsh = 0. Czn create
negative saturation answers.
4 Waxmzn - Smits Model. Requires CEC and Qv data which is hard to
find.
5. Buckle's Method. Use when resistivity is missing.Also used to
find irreducible water saturation SWir in water zones.
6. Many alternate models are covered in this Handbook.
Trim results betweem 0.0 and 1.0 and apply smoothing
funvyion to results if desired.
Material Balance for Water Saturation
Water saturation results must be constrained by the following:
1:
IF Sw < 0
2: THEN Sw = 0
3: IF Sw > 1.0
4: THEN Sw = 1.0
Where:
Sw = water saturation from any method (fractional)
COMMENTS:
Only
the bbulk volume water (dual water) method could create a
negative water saturation.
All
methods can create values greater than 1.0 (100%). If too many
points are over 1.0, water resistivity, shale resistivity, porosity,
and shale volume parameters should be reviewed.
Schlumberger
proposed a smoothing function to reduce statistical noise in saturation
data at both the high and low ends of the spectrum.
SmoothSw - Water Saturation Smoothing
1:
IF Sw > 0.75
2: THEN Sw = (1 - ((16 / 3) (1 - Sw) ^ 3) * (5 - 128 * (1 - Sw)
^ 3))
3: IF Sw < 0.25
4: THEN Sw = Sw + 0.04 * (1 - 4 * Sw) / (1 + 21 * Sw)
Otherwise
Sw is unchanged.
Where:
Sw = water saturation from any method (fractional)
COMMENTS:
The smoothing function is not necessary for hand calculator work,
especially if Sw data is rounded to the nearest 0.05 (or 5%).
The function prevents water saturation from going below 0.04 (4%).
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