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Pipeline transportation of viscous crudes asconcentrated oil-in-water emulsions

 ARTICLE  in  JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING · APRIL 2012

Impact Factor: 1.42 · DOI: 10.1016/j.petrol.2012.04.025

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Pipeline transportation of viscous crudes as concentrated

oil-in-water emulsions

N.H. Abdurahman a,n, Y.M. Rosli a, N.H. Azhari b, B.A. Hayder a

a Faculty of Chemical and Natural Resources Engineering, University Malaysia Pahang (UMP), Malaysiab Faculty of Industrial Sciences and Technology, University Malaysia Pahang (UMP), Malaysia

a r t i c l e i n f o

 Article history:

Received 24 February 2011Accepted 30 April 2012Available online 15 May 2012

Keywords:

pipeline

viscosity

stability

oil-in-water emulsions

heavy crude oil

a b s t r a c t

Stable concentrated oil-in-water (O/W) emulsions were prepared and their application for heavy oil

pipeline transportation was investigated using very viscous Malaysian heavy crude oil. Two Malaysianheavy crude oil samples, Tapis and a blend of Tapis and Masilla, were used to produce heavy crude oil-

in-water emulsions. The diverse factors affecting the properties and stability of emulsions were

investigated. There was a restricted limit of 68 vol% and 72 vol% for crude oil content in the emulsions,

and beyond that limit, the emulsion underwent phase inversion. The study revealed that the stability of 

the oil-in-water emulsion stabilized by Triton X-100 increases as the surfactant concentration

increases, with a subsequent decrease in the crude oil–water interfacial tension (IFT). Increasing the

oil content, the speed and duration of mixing, the salt concentration and the pH of the aqueous phase of 

the emulsion resulted in increased emulsion stability, while increases in the temperature of the

homogenization process substantially reduced the viscosity of the prepared emulsions. Fresh water and

synthetic formation water were used to study the effect of aqueous phase salinity on the stability and

viscosity of the emulsion. The results showed that it was possible to form stable emulsions with

synthetic formation water characterized by a low dynamic shear viscosity.

&  2012 Elsevier B.V. All rights reserved.

1. Introduction

With the combination of an increase in world energy demand

and the decline of conventional oils, heavy crude oils have been

presented as a relevant hydrocarbons resource for use in the

future (Lanier, 1998). Hydrocarbon resources are very important

given that they account for approximately 65% of the world’s

overall energy resources (Langevin et al., 2004). Currently, crude

oil is the most important hydrocarbon resource in the world, and

heavy crudes account for a large fraction of the world’s potentially

recoverable oil reserves (Chilingar and Yen, 1980; Langevin et al.,

2004). However, heavy crude oils only account for a small portion

of the world’s oil production because of their high viscosities,which cause problems in the transportation of these oils via

pipelines (Plegue et al., 1989). Historically, demand for heavy and

extra-heavy oil has been marginal because of their high viscosity

and composition complexity that make them difficult and expen-

sive to produce, transport and refine. Nowadays, Alberta in

Canada and Orinoco Belt in Venezuela are good examples of 

regions producing extra heavy oil. However, an increase in

production of heavy and extra crude oil will take place in several

regions like the Gulf of Mexico and Northeastern China, as it will

be needed over the next two decades to replace the declining

production of conventional middle and light oil. The production of 

heavy crudes is expected to increase significantly in the near

future as low viscosity crudes are depleted  (Plegue et al., 1989).

Currently, there are three general approaches for transportation

of heavy and extra heavy oil: viscosity reduction, drag minimiza-

tion and in-situ oil upgrading (Rafael et al., 2011). Several special

nonconventional methods for the transport of heavy oil have been

proposed, and they include preheating of the crude oil with

subsequent pipeline heating (Layrisse, 1998;   Saniere et al.,

2004), dilution with lighter crude oils (Iona, 1978), partial

upgrading (MacWilliams and Eadie, 1993) and injection of awater sheath around the viscous crude. Each of these methods

has logistic, technical or economic drawbacks.

Although it is often mentioned that the field of hydroproces-

sing catalysis is mature and there are not much compasses for

researcher, the increasing demand of heavy oil has made hydro-

processing a challenging task for refiners as well as for research-

ers   (Rana et al., 2007).   Paraffin wax deposition costs the oil

industry billions of dollars worldwide for prevention and reme-

diation. Paraffin precipitation and deposition in crude oil trans-

port flow-lines and pipelines is an increasing challenge for the

development of deepwater subsea hydrocarbon reservoirs. There

are several paraffin wax treatment methods. The most common

Contents lists available at  SciVerse ScienceDirect

journal homepage:  w ww.elsevier.com/locate/petrol

 Journal of Petroleum Science and Engineering

0920-4105/$ - see front matter &  2012 Elsevier B.V. All rights reserved.

http://dx.doi.org/10.1016/j.petrol.2012.04.025

n Corresponding author. Fax:  þ 60 95492889.

E-mail address:  nour2000_99@yahoo.com (N.H. Abdurahman).

 Journal of Petroleum Science and Engineering 90–91 (2012) 139–144

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removal methods are mechanical heat application using hot oil or

electrical heating, application of chemicals (e.g., solvents, pour-

point dispersants) and the use of microbial products.

Crude oil contains n-paraffin waxes that tend to be separated

from oil when the temperature of crude oil falls below the wax

appearance temperature. With decreasing temperature, the

waxes generally crystallize as an interlocking network of the

sheets, thereby entrapping the remaining liquid fuel in cage-like

structures. When the temperature approaches the pour point,the oil may gel completely causing the cold flow problems such

as blockage of flow pipes or production lines. The pour point is

the lowest temperature at which oil will flow freely under its

own weight under specific test conditions. Several methods

(Bernadiner, 1993;  Hunt, 1996) have been available to improve

the low-temperature properties of crude oil. Pretreatment with

pour point depressants (PDD) is an attractive solution for trans-

portation of waxy crude oils via pipelines.

Another promising pipeline technique is the transport of 

viscous crudes as concentrated oil-in-water (O/W) emulsions

(Gregoli et al., 2006;   Lappin and Saur, 1989).   The technical

viability of this method was demonstrated in an Indonesia pipe-

line (Lamb and Simpson, 1963) and in a 20 km-long, 0.203-m-

diameter pipeline in California. In this method, with the aid of 

suitable surfactants, the oil phase becomes dispersed in the water

phase and stable oil-in-water emulsions are formed. The forma-

tion of an emulsion causes a significant reduction in the emulsion

viscosity; even O/W emulsion might reduce corrosion with a

crude oil with high sulfur content; corrosion may also appear

with use of an aqueous phase, even with the use of formation

water, rich in salts. The produced emulsions have viscosities in

the range of approximately 0.05–0.2 Pa s. Because of this reduc-

tion in viscosity, the transportation costs and transport-assisted

problems are reduced. This method can be very effective in the

transportation of crude oils with viscosities higher than 1 Pa s

especially in cold regions. In addition, because water is the

continuous phase, crude oil has no contact with the pipe wall,

which reduces pipe corrosion for crudes with high sulfur contents

and prevents the deposition of sediments in pipes, as is common

for crudes with high asphaltene contents (Poynter and Tigrina,

1970). The possibility of injecting aqueous surfactant solution

into a well bore to affect emulsification in the pump or tubing for

the production of less viscous O/W emulsions will increase the

productivity of a reservoir (Simon and Poynter, 1968; Steinborn

and Flock, 1982).

The objective of the current research was to investigate the

various factors affecting the preparation of a stable crude O/W

emulsion for two Malaysian oil samples, Tapis crude oil and a

blend of Tapis and Masilla. The study investigated the influence of 

the oil content of the emulsion, the salinity of the water, the

speed and duration of mixing, the pH of the aqueous phase, and

the type and concentration of surfactant.

2. Materials and methods

 2.1. Materials

The crude oil samples used in this study were obtained from

Petronas Refinery at Melaka, Malaysia. A detailed procedure for

the preparation of the crude oil-in-water (O/W) emulsions is

given in a previous report by Abdurahman et al. (2006). Here we

merely describe the main experimental steps. Two crude oils

were used; crude A was Tapis, and crude B is a blend of Tapis and

Masilla. Their compositions and fractions are shown in   Tables 1,

2 and 3  respectively. For the preparation of crude oil-in-water

emulsions, the agent in water method was implemented; that is

the emulsifying agent was dissolved in the continuous phase

(water), and oil was added gradually to the mixture (waterþ

emulsifying agent). Emulsions were agitated vigorously using a

standard three blade propeller at room temperature (25–30   1C).

The volume of water that settled to the bottom over time was

measured using scale on the beaker. The prepared emulsions

were used to check for W/O or O/W emulsions. All emulsions

investigated were oil-in-water emulsions (water as the contin-

uous phase). The surfactant used in this study was Triton X-100

(polyethylene glycol octylphenyl ether), which has a chemical

formula of C33H60O10. This surfactant is a nonionic hydrophilic

surfactant that is suitable for use in the production of O/W

emulsions.

 2.2. Experimental procedure

 2.2.1. Sample preparation and procedures

The crude oil samples were obtained from Petronas Refinery at

Malaka city, two types of crude oils were collected. Different

samples of oil-in-water emulsions were prepared using the two

crude oils and tab water. Emulsions were prepared in 500 mL 

graduated beakers with ranges by volume of water and oil phase.

The water phase is tab water. The emulsions were agitated

vigorously using a standard three blade propeller. The prepared

emulsion was used to check for W/O or O/W emulsions. All

emulsions investigated were O/W emulsion (water-continuous

phase).

Two series of experiments were performed using two different

samples of crude oils. In both series, the influence of the

surfactant concentration (0.3–2.5 wt%), the speed of mixing

 Table 1

Physical properties of crude oils: A and B.

Crude oil Crude A Crude B

Density (gm cm3) 0.874 0.788

Viscosity (Pa s) 0.028 0.010

API gravity 18.0 20.00

Surface tension (mN m1) at 30  1C 30.30 22.50

Interfacial tension (mN m1) at 30  1C 28.80 20.35

 Table 2

Chemical properties of the crude oils used in this study.

Crude oil Crude A Crude B

Asphaltenes (wt%) 1.50 0.87

Resins (wt%) 13.50 9.40

Aromatics (wt%) 25.00 23.00

Saturates (wt%) 60.00 66.73

 Table 3

Viscosity of crude A and obtained blends B, interfacial tension with oil contents.

Salini ty Oil content Viscosity Interfacial tension

Nacl conc. Crude A Crude B Crude oil A Crude oil B

(%) (vol%) (Pa s) (Pa s) (mN/m) (mN/m)

0 30 1.200 0.900 28.80 20.35

1.5 40 1.620 1.100 28.20 20.26

2.5 50 1.670 1.200 27.77 18.78

3.5 60 1.700 1.270 26.32 15.83

4.5 68 1.780 1.285 24.00 14.44

5.5 70 1.820 1.200 23.66 14.00

5.5 72 1.750 1.190 22.70 13.81

5.5 80 1.890 1.281 21.90 13.56

5.5 85 – 1.290 21.90 12.80

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(1000–2000 rpm), the duration of mixing (5–15 min), the pH of 

the aqueous phase (6–7.8), the salt concentration and the tem-

perature of homogenization (25–90   1C) on the stability and

viscosity of the emulsion was investigated. In each series of 

experiments, oil-in-water (O/W) emulsions were prepared using

various amounts of the oil samples while other parameters were

kept constant at desirable values. Therefore, the maximum limit

of oil content for each sample was determined. Beyond that limit,

phase inversion occurred. The phase inversion of crude oil A

(Tapis) occurred at oil content of 72 vol% while crude B (blends

Tapis and masilla) occurred at oil content of 68 vol%.

The emulsion stability was investigated using the following

equation and the results have been tabulated in  Table 4:

Emulsion stability ¼ 1water separated ð%Þ

water content ð%Þ  ð100Þ

For example: oil content 72%, amount of water separated 7%,

by applying the above equation, the O/W emulsion stability will

be 75%, Table 4.

 2.3. Pour point measurement 

The pour point of the crude oil samples was measured using

Cloud and Pour Point apparatus Model Stanhope-Seta with Auto

Frigistat. The procedure followed the Standard Test Method

(ASTM Designation D97-93). After preliminary heating, the sam-

ples were cooled at a specified rate and were examined at an

interval of 3   1C. The lowest temperature was recorded as the pour

point at which the movement of the specimen was observed.

3. Results and discussion

 3.1. Effect of oil content 

The effects of the oil content of the emulsion on its stability,

pour point and dynamic shear viscosity were investigated. Theconcentration of Triton X-100 in water was kept constant, at

3 wt% at a temperature of 50   1C and a pH of 7. The speed and

duration of mixing were 1700 rpm and 15 min, respectively. For

each particular type of crude oil, the oil content of the emulsion

was varied from 30 to 80 vol% with respect to the total volume of 

the emulsion.

Table 4 shows the data for the influence of oil content on both

the stability and pour point of the O/W emulsion. It can be seen

from these results that the stability of the emulsion remained

unchanged after six days for the emulsion containing 72 vol%

crude oil A. However, for emulsion containing 70, 60, 50, 40, and

30 vol% crude oil, some water separation occurred; the amounts

of separated water were 30%, 45%, 50%, 65% and 70%. These

results were expected because, as the volume fraction of the

dispersed phase increases, the rate of coalescence increases owing

to the increased entropy for effective collisions between the

dispersed droplets (Menon and Wasan, 1985). The influence of 

the oil content of the emulsion on its pour point is a very

important parameter to study; to be sure that the pour point of 

the prepared O/W emulsion does not increase and cause trans-

portation problems in pipelines at low temperatures. Therefore,

the pour points of the emulsions with different oil contents were

obtained together with the pour point of Tapis crude oil ( þ20 o

C),and the results are listed in   Table 4. For all of the oil contents

studied, the measured pour points were found to be lower than

those of the Tapis crude oil indicating that the formation of an

O/W emulsion for a particular crude oil decreases its pour

point value.

For the different oil contents of the emulsion, the surfactant

concentration was kept constant, with respect to the total emul-

sion volume (0.3 wt%). The surfactant concentration in the aqu-

eous continuous phase (water) increased as the oil content

increased and consequently the water content decreased. The

actual surfactant concentration in the aqueous phase for each oil

content is given in Table 4.

Fig. 1 is a plot of the dynamic viscosity of the emulsion versus

the oil content of the emulsion expressed in vol% at different

temperatures. It is clear from these results that decreasing the oil

content or conversely increasing the water content of the emul-

sion is accompanied by a decrease in the emulsions apparent

viscosity.   Fig. 2   again is a plot of the dynamic viscosity of the

emulsion versus the oil content of the emulsion expressed in vol%.

By increasing the oil content up to 72 vol% (Crude Oil A) and

68 vol% (Crude Oil B), the viscosity reached its maximum, beyond

these values, the emulsions slightly decreases. However, beyond

this limit the viscosity increases significantly due to the occur-

rence of phase inversion.

The effective dynamic viscosity of Tapis crude oil decreased

from 2 Pa s to 0.1 Pa s at 30   1C for the 50% oil emulsion. From the

economic point of view, it is more profitable and cost-effective to

reduce the viscosity of the crude oil using the minimum amount

of water.

 3.2. Effect of mixing speed on the stability and viscosity of the

emulsion

The effect of the dynamic viscosity of the Tapis crude oil-in-

water emulsion was investigated for five different mixing speeds,

700, 900, 1200, 1500, and 1700 rpm at 50   1C for 15 min at a fixed

 Table 4

Stability and pour point of the emulsions containing different oil contents.

Oil

content

% Water separation

after six days at 30  1C

% Emulsion stability

after six days at 30  1C

Surfactant

conc.

Pour

point

(vol%) (wt%) (1C)

100 – – –   þ20

80 0 100 2.5   þ12

72 7 75 2.5   þ8

70 12 60 2.5   þ860 18 55 2.0   þ8

50 27 46 1.5   þ6

40 42 30 1.0   þ5

30 48 31.43 0.3   þ5

20 30 40 50 60 70 80 90

Oil Content (Vol.%)

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

   V   i  s  c  o  s   i   t  y   (   P  a .  s

   )

 30 oC

 50 oC

 70 oC

Fig. 1.  Dynamic shear viscosity of emulsions as a function of the oil content at

different temperatures.

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surfactant concentration (2.5%), using synthetic formation water

as the continuous phase, and with a 72 vol% oil content. From

these observations, it can be deduced that the phase inversion

point is in the range of 68–72% oil.  Fig. 3 demonstrates the effect

of mixing speed on the viscosity and stability of the emulsions.

Increasing either the speed or duration of mixing has a similar

effect on the emulsion’s quality. The increase in speed or duration

of mixing has a slight increasing effect on the viscosity of the

emulsions and increases the stability of the emulsions up to a

desirable level. On the other hand, using a mixing speed of less

than 900 rpm and a mixing duration of less than 7 min would

significantly reduce the quality of the emulsions. For a crude oil-

in-water emulsion with a specified volume fraction of crude oiland a specified surfactant concentration, increasing the speed and

duration of mixing increases the production of droplets with

smaller sizes, which causes an increase in the interfacial area and

particle-to-particle interactions, which thus increases the stability

of the emulsion. At the same time, decreasing the size of the oil

droplets, i.e. the dispersed phase, results in a slight increase in the

viscosity of the emulsions (Stachurski and Michalek, 1996; Zaki,

1997). The obtained observations for the increase in the emulsion

viscosity due to the increase in the agitation speed, which

produces droplets of smaller size, are in agreement with the

findings of  Pal et al. (1992), as well as with those of  Briceno et al.

(1997). As the volume of the dispersed phase increases, the

continuous phase must spread out further to cover all the

droplets. This spreading out of the continuous phase increases

the likelihood of impacts between droplets, thus decreasing the

stability of the emulsion.

 3.3. Effect of the surfactant concentration on the stability and

viscosity of the emulsion

The surfactant concentration required for stabilizing the emul-

sion and forming an emulsion with acceptable viscosity was

investigated. To prepare the O/W emulsions, the oil content of the emulsion was kept constant at its optimum value, i.e. 72 vol%,

the other conditions were a temperature of 30   1C, pH of 7, a

mixing speed of 1700 rpm and a mixing duration of 15 min. The

concentration of Triton X-100 surfactant in water was varied from

0.125 to 1.5 wt%.  Fig. 4   illustrates the effect of the surfactant

concentration on the viscosity and stability of the emulsions.

Increasing the concentration of the surfactant resulted in a

slight increase in the viscosity of the emulsion, and the stability

significantly increased. Increasing the surfactant concentration

results an increase in the number of barriers between the two

phases and provides a better distribution of dispersed droplets in

the continuous phase. It is notable that Triton X-100 is a viscous

liquid. Thus increasing its concentration in the emulsion increases

the viscosity of the emulsion (Eirong and Lempe, 2006). At thesame time, increasing the surfactant concentration reduces the

interfacial tension, which facilitates the splitting of droplets into

smaller ones. The latter would result in a more stable emulsion

with a higher viscosity (Sakka, 2002). It is clear from the above

mentioned results that, increasing the surfactant concentration

increases the emulsion stability; this increase in stability could be

correlated to the oil/water IFT.   Fig. 5   depicts a plot of the

surfactant concentration in the synthetic formation water versus

the crude oil/water IFT measured at 30   1C. As clearly demon-

strated by this figure, the increase in the surfactant concentration

results in an increase in the number of surfactant molecules

adsorbed at the oil–water interface. The adsorbed surfactant

molecules provide a steric barrier to the coalescence of the

dispersed oil droplets as a result of the nonionic nature of the

surfactant Singh and Pandey (1991). The appropriate surfactant

concentration should be chosen based on the surfactant cost and

the economy of the process.

 3.4. Effect of temperature on the stability and viscosity of the

emulsion

One of the important methods that can be used to lower the

viscosity of heavy crude oil and therefore to enhance the flow-

ability is to change the temperature. Temperature has a strong

20 30 40 50 60 70 80 900.8

1

1.2

1.4

1.6

1.8

2

Oil content (vol.%)

   V   i

  s  c  o  s   i   t  y              (   P  a .  s

              )

Crude oil A

Crude oil B

Fig. 2.  Dynamic viscosity versus the oil content of the emulsion.

600 800 1000 1200 1400 1600 1800

Mixing Speed (rpm)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

   V   i  s  c  o  s   i   t  y   (   P  a .  s

   )

 30 oC

 40 oC

 60 oC

Fig. 3.  Dynamic viscosity of the emulsions as a function of mixing speed.

Fig. 4.  Emulsions stability as a function of mixing speeds at constant temperature

and surfactant concentration.

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effect on viscosity and viscous behavior. This effect determines

the flow behavior of the crude oil in terms of the viscosity–shear

rate relationships.  Fig. 6 shows the effect of temperature on the

viscosity–shear rate for heavy crude oil over the range of 30–80   1C

in 101   increments. The crude oil shows non-Newtonian shear

thinning behavior over the range of shear rates from 75 to

700 s1 in which the apparent viscosity decreases considerably

with temperature and is reduced by one half when it is heated

from 30 to 80   1C. The viscosity differences were larger at low

shear rates than at high shear rates.

 3.5. Effect of pH on emulsion stability

Water phase pH has a strong influence on emulsion stability.

The stabilizing, rigid-emulsion film contains organic acids and

bases, asphaltenes with ionizable groups, and solids. Adding

inorganic acids and bases strongly influences their ionization in

the interfacial films and radically changes the physical properties

of the film by the charges at the interface, along with the

electrostatic double layer repulsion effect. The pH of the water

affects the rigidity of the interfacial films. Brine composition has an

important effect (in relation to pH) on emulsion stability.   Fig. 7

shows the effect of a bicarbonate brine and fresh water on

emulsion stability as a function of pH. Optimum pH (for water

separation) changes from approximately 10 for fresh water to 7 for

brine solution. This is because of the ionization effect (i.e., associa-

tion/interaction of ions present in the brine with the asphaltenes).

4. Conclusions

The oil-in-water (O/W) emulsions were successfully prepared

using two crude oil samples, the Tapis and a blend of Tapis and

Masilla. The effective viscosity of the two crude oils decreased

when it was emulsified with water in the presence of Triton

X-100. The viscosity of the emulsion was found to decrease as the

oil content of the emulsion decreased, the speed of mixing

decreased, and the salinity of the aqueous phase decreased.

The stability of O/W emulsions of both samples was found to

decrease as the oil content of the emulsion increased up to the

phase inversion point. After this point the emulsion converts to a

W/O emulsion, and the stability of the emulsion begins to

increase with increasing oil content. The phase inversion of crude

oil A (Tapis) occurred at oil content of 72 vol% while crude B

(blend Tapis and masilla) occurred at oil content of 68 vol%.

The stability of O/W emulsions of both samples was found to

increase with increases in the surfactant and salt concentrations,

the speed and duration of mixing, the pH of the aqueous-phase

and the temperature of homogenization.

References

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Lappin, G.R., Saur, J.D., 1989. Alpha Olefins Applications Handbook. CRC Press,

New York.

Fig. 5.  Interfacial tension as a function of water salinity at different surfactant

concentrations.

0 100 200 300 400 500 600 700 800

Shear Rate (s-1)

5

6

7

8

9

10

11

   V   i  s  c  o  s   i   t  y   (   P  a .  s

   )

 30 oC

 40 oC

 50 oC

 60 oC

 70 oC 80 oC

Fig. 6.  Effects of temperature on the viscosity of heavy crude oil.

0 2 4 6 8 10 12

0

10

20

30

40

50

60

70

80

90

   %   W

  a   t  e  r   S  e  p  a  r  a   t   i  o  n

 pH 

Brine solution

Fresh water 

Fig. 7.   Effect of brine and pH on emulsion stability.

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