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       Material Balance for Water Saturation   

Material Balance for Water Saturation
Water saturation results must be constrained by the following:

SwBAL - Material Balance for Water Saturation
      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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