Emulsions of Heavy Crude Oils II. Viscous Responses
and Their Influence on Emulsion Stability Measurements
(J. Disp. Sci. Tech. 31, 2010)
A. Silset, P. V. Hemmingsen, StatoilHydro RCT
J. Sjöblom, Ugelstad Laboratory NTNU
A. Hannisdal, Aibel Technology
Background
JIP 2003-2006: Particle-stabilized emulsions and heavy crude oils
position a)
Composition
 SARA
 Water
 Solids
 Acidity
Oil
Spectroscopy

 Signatures in IR and NIR
 Asphaltene precipitation
potential
Bulk Properties
 Density
 Molecular weight
 Rheology
 Electrical properties
Interfacial Prop.
 Interfacial tension
 Dilational relaxation
Stability
 Droplet size
 Electric field
 Gravity
2
Interpretation
and modelling
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Asph.
wt.%
1.2
1.9
5.0
3.1
1.2
2.8
1.7
12.9
1.2
0.8
0.6
3.9
4.3
1.0
4.6
3.8
0.2
10.2
0.2
5.4
0.6
2.8
0.2
0.1
2.3
0.3
3.4
2.2
6.2
3.3
Interfacial
properties b)
Bulk properties
TAN
mg KOH/g
4.2
0.6
1.3
2.3
0.0
7.5
1.4
1.1
0.0
2.9
2.9
0.4
5.2
0.4
3.4
0.6
1.8
3.7
0.2
0.0
2.5
1.7
0.7
0.9
2.2
0.5
2.5
0.0
0.8
1.9
MW
g/mol
368
278
343
536
246
429
309
473
268
319
242
338
527
263
436
335
268
435
235
295
374
345
247
227
334
204
366
331
345
270
Density
40 oC
(g/cm3)
0.95
0.88
0.93
0.95
0.85
0.98
0.90
0.96
0.86
0.91
0.87
0.93
0.98
0.87
0.94
0.92
0.89
0.97
0.85
0.91
0.92
0.92
0.87
0.88
0.92
0.84
0.94
0.90
0.90
0.86
Viscosity
40 oC
(cP)
276
18
118
2286
9
2269
36
5418
13
49
11
109
23397
13
505
81
16
2497
8
33
138
104
11
12
82
5
225
36
69
10
Viscosity
60 oC
(cP)
80
9
43
515
4
464
17
1031
6
20
5
40
2880
7
151
33
8
528
3
14
48
40
6
6
31
2
72
16
29
5
IFT
60 oC
mN/m
10.4
18.3
21.3
16.9
12.0
10.2
17.4
18.8
17.9
11.1
14.9
13.4
10.7
15.3
17.2
14.0
11.4
11.0
16.1
16.2
12.4
17.8
8.3
10.9
16.5
12.9
14.4
23.9
23.2
5.1
E’
60 oC
mN/m
19
17
7
8
18
20
10
6
14
12
12
7
12
18
7
7
25
7
11
19
23
9
17
32
16
17
14
14
15
15
Outline
Evaluation of the critical electric field cell (ECRIT) for quantifying emulsion stability
Theoretical expression for droplet transport
Results
Viscosity
Temperature
Water cut
Conclusions
Recommendations
Experimental design
Experimental setup
3
ECRIT
A common way of quantifying emulsion stability
(a)
Plexiglass
(b)
(CEF)
Sample compartment
Teflon spacer
A
DC
<100 V
Brass plate
(b)
(a)
50 mm
Figure: The graph shows the current through the CEF
cell with an oil continuous emulsion subjected to an
increasing DC electrical field.
4
ECRIT
Which forces are dominant in a homogeneous background field?
Dipole coalescence (DC/AC)
Electrophoresis (DC, charged droplet)
Polarization causes attractive forces
between droplets
Forces due to charged droplets
Relaxation time for charged droplets:
E0
24πε1ε 0 r 6 E0
F=
( d + 2r ) 4
40 oC:
2
τaverage = 6.0 x 10-4 sec
τ=
ε 1ε 0
σ1
E0
δ ++
δ
-
-
-
r
δ++
δ
+
+
+
F
-
-
-
r
+
+
+
d
5
Figure: Dipole coalescence between two water
drops (no permanent charge) in a horizontal AC
or DC electric field (simplified)
Figure: A droplet is charged in contact with a non-insulated
electrode (DC field) and can collide with a droplet which has
been charged from the opposite electrode (Eow).
Theoretical model
Viscous drag (Stokes) and point-dipole approximation
Characteristic time for destabilization:
 8η   dE0 
  

5
ε
dt
  

1/ 3
τ theo
−2 / 3
 π 


6
φ
 w 
5/ 3
1/ 3

− 1

Several assumptions (specified in the manuscript)
6
E0=0
Results
Viscosity
4.5
limit
4.0
3.5
limit
6
CEF (kV/cm)
3.0
E0=0
2.5
CEF
2.0
1.5
1.0
0.5
0.0
0.00
0.01
0.02
0.03
0.04
dE/dt (kV/cm s -1)
Figure: The figure shows electrocoalescence of 30 water-in-crude oil
emulsions (φw = 0.3 vol/vol) with a background DC field.
7
1000
?
τexp (sec)
750
500
250
0
0
50
100
150
200
250
τtheo (sec)
Figure: The characteristic time of destabilization (τexp) of emulsions (φw = 0.3, T = 40 oC) is
compared to the theoretical (τtheo) value of droplet approach.
800
Drop-plane distance (µm)
Drop-plane distance (µm)
800
600
400
Impact dominated
by film thinning
200
0
600
Impact dominated by
electrical forces
400
200
0
0
0.2
0.4
Time (s)
0.6
0.8
0
0.1
0.2
0.3
Time (s)
Figure: Falling drop experiments in a vertical 100 Hz background field of 1kV/cm (left)
and 4 kV/cm (right) (S.M. Hellesø).
τ theo (60° C)
τ theo (40° C)
0.9
[η(60)/η(40)]^1/3
0.8
0.7
0.6
0.5
0.4
1
 8η   dE0 
  

 5ε   dt 
1/ 3
τ theo
10
−2 / 3
100
1000
η(40) (cP)
1/ 3
 π 5/ 3 

 − 1
 6φw 

10000
100000
0.9
0.9
0.8
0.8
0.7
0.7
0.6
0.6
0.5
0.5
0.4
0.4
100000
1
 8η   dE0 
  

 5ε   dt 
1/ 3
τ theo
10
−2 / 3
100
1000
η(40) (cP)
1/ 3
10000
ln[η(60)]/ln[η(40)]
[η(60)/η(40)]^1/3
τ theo (60° C)
τ theo (40° C)
1/ 3
5/ 3
1/ 3
−2 / 3 

 π 5/ 3 


8
dE
π
   0
τ theo lnη   
=

 − 1
 
 − 1
5
ε
dt
6
φ
  
  w 

 6φw 



 8η   dE0 
  

 5ε   dt 
1/ 3
τ theo
−2 / 3
1/ 3
1/ 3
5/ 3
 π 5/ 3 
1/ 3
−2 / 3 



π
 8   dE 

τ theo lnη    0  
 − 1 =
 − 1
 6φw 

 5ε   dt   6φw 

Figures: The characteristic time of destabilization (τexp) of emulsions is compared
to the theoretical (τtheo) time of destabilization.
Results
Temperature
Figure: The characteristic time of destabilization (τexp) of emulsions at
different temperature (4-80 oC) is compared to the theoretical time (τtheo) from
the modified expression.
13
Results
Water cut
9
Beetge 120 F
Prediction 120 F
8
Beetge 150 F
Prediction 150 F
Beetge 180 F
Prediction 180 F
7
1
6
φw
Point dipole approximation :
CEF (kV/cm)
Beetge :τ theo ∝
5
4
3
1/ 3
τ theo
  π 5 / 3 
 − 1
∝  
  6φw 



2
1
0
0
2
4
6
8
10
X
Figure 12: Critical electric field results from Beetge. The same
data are plotted as a function of X=1/φw according to Beetge,
and X=[(π/6φw)5/3-1]1/3 according to our expressions .
14
Conclusions
A semi-empirical model seems to capture the effect of droplet-droplet approach in
emulsions of very different oils with high visosity, different water cut, and different
temperature.
1/ 3
 8 
τ theo lnη  
=
 5ε 
 dE0 


 dt 
−2 / 3
1/ 3
  π 5 / 3 

 − 1
φ
6
 w 

For this specific crude oil matrix, the flocculation step seems to dominate the
overall destabilization process.
It should be possible to predict separation in an industrial process from small scale
experiments
15
Recommendations
Experimental design
Create a theoretical model for the flocculation step
Use well defined systems instead of a crude oil matrix
Demonstrate the validity of a model
The model will correctly explain the overall stability of systems which are dominated by the
flocculation step
Understand the interfacial chemistry of the coalescence step
Identify compounds which make the process dominated by the coalescence step
Treat these
The system will be controlled by the flocculation step and can be explained by the model
16
Recommendations
Experimental setup
Cell
Temp.
Long settling height
Minimal wall effects
Good resolution for unstable emulsions
Level and interface detection
Water cut in different heights
Amount of free water
Differensiate between flocculation and coalescence
Electrocoalescence
Include electrical fields
Quantify the degree of droplet growth by electrical forces
17
Power supply
Logger
PC