Laboratory Determination of Fluid Saturations

Conventional Core Analysis

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

Retort Distillation Apparatus

Coolingwater out

Coolingwater in

Condenser

CoresampleHeating

element1000-1100 F

Graduated Cylinder

Retort Distillation Method

• Advantages– Rapid (less than one hour)– Direct measurement of both oil and water

volumes recovered– Adequate accuracy

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

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

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

Retort Distillation Calculations

measuredocorrectiono VFV

p

measuredww V

VS

p

oo V

VS

Vw = Volume of water, cm3

Vo = Volume of oil, cm3

Vp = Pore volume, cm3

Fcorrection = Volume correction factor,

dimensionless

owg SS1S

sourceanotherfrombp VV

Solvent Extraction Apparatus

Condenser

Graduate tube

Thimble and core

Solvent

Electric Heater

Modified from Amyx, Bass and Whiting, 1960

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

Solvent Extraction Method

• Disadvantages– slow (can take several days)– oil volume not directly measured

• oil remains in solvent

Solvent Extraction Calculations

o

wwdryio ρ

ρVWWV

p

ww V

VS

p

oo V

VS

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

owg SS1S