Saturation

• Volume of phase to pore volume

• Wettability

• Tortuosity

• Mobile vs immobile

1) Swir -irreducible water saturation, below which water cannot flow. 2) Swc -connate water saturation existing on discovery of the reservoir. It may or may not be irreducible. 3) Swi -may mean irreducible, connate, or interstitial, which means saturation among the interstices, or pores. Interstitial may or may not signify irreducible. It may be the value on discovery of the reservoir, or the value at any time thereafter. Swi may also mean initial or original, which truly means the water saturation on discovery, but it may or may not be irreducible.

Saturation

Saturation distribution in a reservoir

Saturation

Factors affecting fluid saturations

• Fluid invasion

• Release of confining pressure

• Thermal affects

Factors affecting fluid saturations

Factors affecting fluid saturations

Influence of mud type on saturations

Oil67.6%

Wtr32.4%

Oil53.4%

Oil

26.7%

67.6%Wtr46.6%

Wtr38.5%

Gas

34.8%

Original After

flushing

At

surface

Water-based Muds

Oil50.9%

Wtr49.1%

Oil

32.9%

Oil

26.7%

Wtr49.1%

Wtr47.7%

Original After

flushing

At

surface

Oil-based Muds

Filtrate18%

Gas 25.6%

Measurement of Fluid Saturation

1. Retort method

- evaporation of the fluids in the pore space

2. Dean-Stark extraction method

- the leaching of fluids in the pore space

Measurement of Fluid Saturation

Retort method • sample is sealed inside an aluminum cell

and then heated in stages from 400 F to

1100 F

• Advantages: fast, multiple samples run

Picture of a conventional retort [CoreLab,1983]

Measurement of Fluid Saturation

Disadvantages of Retort method

Retort oil correction curve [CoreLab, 1983]

Retort water calibration curves [CoreLab,1983]

• Coking effect - heating process burns oil to the pore surfaces.

• results in oil recovery less than the initial amount in the sample.

• Empirical correction

• removal of both pore water and water of crystallization.

• Results in high water recovery

Volume of water in pores

Crystallized water

Measurement of Fluid Saturation

Dean-Stark extraction method • vapor of a solvent rises through the core

and leaches out the oil and water.

• water condenses and is collected in a graduated cylinder.

• solvent and oil continuously cycle through the extraction process.

• A typical solvent is toluene, miscible with the oil but not the water.

• Advantage: accurate

• Disadvantage: long time

o*p

V

wtrW

dryW

wetW

oS

Measurement of Fluid Saturation

Example of Dean-Stark extraction method to determine saturations • Obtain the mass of the saturated sample = 57 gms.

• Determine the bulk volume by nondestructive means = 25 cc

• Determine the oil density = 0.88 gm/cc

• Place the sample in the extraction apparatus and heat the solvent.

Record the volume of water collected and when the reading

becomes constant – stop. Vw = 1.4 ml

• After cooling, remove the core and dry, obtain dry weight = 53 gms.

• Using the saturation method, resaturate the sample with

fresh water ( = 1.00 gm/cc) and weigh. = 58 gms.

Measurement of Fluid Saturation

Example of Dean-Stark extraction method to determine saturations • Calculate the pore volume and porosity,

• Calculate the water saturation

• Calculate the oil saturation

• Calculate the gas saturation

%2025

5

cc500.1

5358p

V

%285

4.1w

S

%5988.0*5

00.1*4.15357o

S

%1359.028.01g

S