Laboratory Determination of Fluid Saturations

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Laboratory Determination of Fluid Saturations
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Conventional Core Analysis

• Two common methods will be discussed
• Retort Distillation
• Solvent Extraction

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Retort Distillation Apparatus
Core sample
Heating element
1000-1100 ?F
Cooling water in
Cooling water out
Condenser
Graduated Cylinder
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Retort Distillation Method

• Advantages
• Rapid (less than one hour)
• Direct measurement of both oil and water volumes
  recovered
• Adequate accuracy

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Retort Distillation Method

• Disadvantages
• High temperatures (1,000 - 1,100 ?F)
• destroys core sample
• water of crystallization in clays may vaporize
  and must be accounted for
• cracking and coking of oil
• cracking is breaking of long chain hydrocarbons
  into smaller chain hydrocarbons, which may not be
  recondensed
• coke is impure carbon residue formed from oil

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Determining Water of Crystallization

• Water from pores is recovered first
• If flattening of curve is not apparent then
  estimating water recovered from pore space can be
  innaccurate
• Later, water of crystallization is recovered at
  higher temperatures
• This is destroys the core sample

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Effects of Coking and Cracking of Oil

• Coking and cracking tend to cause only part of
  oil from pores to be recovered
• We must scale up the volume of recovered oil to
  reflect the volume of oil originally in the pores
• Scaling factor depends on API gravity of oil
• Coke formation destroys core sample

Retort Distillation Scaling Factor for Recovered
Oil
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Retort Distillation Calculations
Vw Volume of water, cm3 Vo Volume of oil,
cm3 Vp Pore volume, cm3 Fcorrection Volume
correction factor, dimensionless
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Solvent Extraction Apparatus
Condenser
Graduate tube
Thimble and core
Solvent
Electric Heater
Modified from Amyx, Bass and Whiting, 1960
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Solvent Extraction Method

• Advantages
• accurate determination of water saturation
• non-destructive to core samples
• determination of water saturation by solvent
  extraction can be made part of the core sample
  cleaning process for small incremental cost

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Solvent Extraction Method

• Disadvantages
• slow (can take several days)
• oil volume not directly measured
• oil remains in solvent

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Solvent Extraction Calculations
Wi Initial core weight, gm Wdry Core weight
after leaching, gm Vw Volume of water
collected, cm3 Vo Volume of oil, cm3 Vp
Pore volume, cm3 ?w Density of water,
gm/cm3 ?o Density of oil, gm/cm3 ?g Density
of gas is assumed negligible