Correlation between phase
behavior and IFT
Leslie Zhang
Phase behavior after 2 months with 0.2% (left) and
0.5% (right) NI blend.
0.2% NI blend/1% Na2CO3/x% NaCl @
soap/synthetic surfactant ratio of 0.35 (WOR=3:1)
2 months settling at room temperature
x=
2.0
3.0
3.2
3.4
3.6
3.8
4.0
0.5% NI blend/1% Na2CO3/x% NaCl @
soap/synthetic surfactant ratio of 0.14 (WOR=3:1)
2 months settling at room temperature
x= 3.0 3.5 4.0 4.3 4.5 4.7 5.0
Solubility ratios of 0.2% NI blend /
1% Na2CO3 / NaCl
Huh Correlation, 1979
 l3 

c
Rl 3
2
interfacial tension between excess oil or aqueous phase
and middle phase,
3
Rl3: solubility ratio of oil or water by surfactant
c: a constant with a typical value of 0.3.
Comparison of IFT measured by spinning drop measurements
using standard procedure and that estimated by Chun-Huh
correlation of 0.2% NI blend/1% Na2CO3/NaCl. c=0.3.
Solubility ratios of 0.5% NI blend /
1% Na2CO3 / NaCl
IFT estimated by Chun-Huh correlation
of 0.5% NI blend/1% Na2CO3/NaCl, c=0.3.
Phase behavior of 0.2% NI blend/1% Na2CO3/x% NaCl, 40 days of settling.
Thin creamed oil-rich layers exist at salinity of 2-3.4% NaCl.
S/SR=1
x=
2.0
Soap / Synthetic surfactant ratio = 0.35
2.0
3.0
3.2
3.4
3.6
3.8
4.0
Conclusions
• The measured low IFT over a wide range of
salinity is consistent with the solubility ratio
data.
• The thin layer of oil-rich emulsion may be
responsible for the above observation.
• The dependence of this layer on the amount
of oil present suggests that it may be due to
the presence of the naphthenic soaps.