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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.
This
webpage version is the copyrighted intellectual
property of the author.
Do not copy or distribute in any form without explicit
permission. |
Material Balance for Water Saturation
Water saturation results must be constrained by the following:
1:
IF Sw < 0
2: THEN Sw = 0
3: AND SwNEG = SwNEG + 1
4: IF Sw > 1.0
5: THEN Sw = 1.0
6: AND SwPOS = SwPOS + 1
Where:
Sw = water saturation from any method (fractional)
SwNEG = counter for number of negative saturation values
SwPOS = counter for number of saturation values over 1.0
COMMENTS:
Only the bulk 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.
RECOMMENDED
PARAMETERS:
None.
NUMERICAL
EXAMPLE:
None.
Schlumberger
proposed a smoothing function to reduce statistical noise in saturation
data at both the high and low ends of the spectrum.
SwSMO - 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%).
RECOMMENDED
PARAMETERS:
None.
NUMERICAL
EXAMPLE:
None.
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