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Heavy Crude Oil Viscosity Reduction for Pipeline Transportation
Article in Energy Sources · February 2002
DOI: 10.1080/00908310252774417
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Basma Yaghi
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Zarqa University
Sultan Qaboos University
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Heavy Crude Oil Viscosity
Reduction for Pipeline
Transportation
Basma M. Yaghi & Ali Al-Bemani
Published online: 10 Nov 2010.
To cite this article: Basma M. Yaghi & Ali Al-Bemani (2002) Heavy Crude Oil Viscosity
Reduction for Pipeline Transportation, Energy Sources, 24:2, 93-102
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Energy Sources, 24:93–102, 2002
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Heavy Crude Oil Viscosity Reduction for
Pipeline Transportation
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BASMA M. YAGHI
ALI AL-BEMANI
Sultan Qaboos University
College of Engineering
PMRE Department
Khoud, Oman
The approaches used for reducing the viscosity of a heavy crude include heating,
blending with a light crude and with kerosene, and forming oil-in-water emulsions.
Heating had a dramatic effect on the heavy crude viscosity, but it failed to achieve
a practical level; consequently, blending the heavy crude with either light crude or
kerosene was attempted and further reduction was achieved, but substantial amounts
of these expensive diluents are required.
Alternatively, emulsion formation was carried out, and it was established that
a practical level of reduction is achievable at 70–75% oil content, in the high shear
rate range, and at 30–50° C.
The effect of temperature on the viscosity of the crude oil mixtures and emulsions
can be Ž tted on the American Society for Testing and Materials (ASTM) double-log
model with an average deviation of 7.2–9.4%.
Introduction
In many parts of the world, heavy crude oil has to be transported by pipelines from
the place of production to reŽ neries or ports. However, pipeline transportation is very
expensive and sometimes impossible because of the crude’s low mobility and high viscosity. Several methods have traditionally been proposed to enhance the mobility of heavy
crudes for pipeline transportation; these include heating crude oils or diluting them with
lighter fractions of hydrocarbons . Hardy et al. (1988) proposed and Ž eld-tested pipeline
transportation of heavy crude oil as oil-in-water emulsions that contain high fractions
of oil.
A large number of studies, mostly experimental in nature, have been carried out
on oil-water emulsions (Zaki, 1997; Urdahl et al., 1997). However, the results of these
studies are not uniform and are sometimes contradictory. The reason is that the viscosity
behavior of emulsions is complex and depends on such factors as base sediment and
water (BS&W), temperature, shear rate, type and concentration of surfactant, and the
Received 12 September 2000; accepted 15 March 2001.
We would like to thank Shimizu Corporation, Tokyo, Japan, for a research grant that enabled
this project to proceed. Our thanks go to Petroleum Development Oman (PDO) for supplying us
with the heavy and light crude oils.
Address correspondence to Basma M. Yaghi, Sultan Qaboos University, College of Engineering, PMRE Department, P.O. Box 33, Khoud 123, Oman.
93
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94
B. M. Yaghi and A. Al-Bemani
components of the crude itself. Because of the complex behavior of emulsions, the results
obtained from a study on a certain crude is difŽ cult to apply to another. Consequently,
oil companies investigate on their own the speciŽ c crude that they produce the type of
emulsion most appropriate.
The oil used in this study is a heavy crude with a viscosity of approximately 15,000 cp
at 20° C; i.e., conventional pipeline transportation is impossible. A research carried out on
this oil (Shikoku Research Institute, 1999) showed that it has a high hydrogen content,
thus emitting lower carbon dioxide at the same caloriŽ c level as the regular fuel oil that
is used in power plants. This cheap oil is a potential fuel for power plants but its pipeline
transportation is problematic. The pipeline  ow behavior of the emulsions prepared with
the same heavy crude oil was studied by Al-Asmi et al. (1997). Their experimentation was
conducted in the absence of surfactant; consequently, stable emulsions were not obtained
at any BS&W ratio. The viscosity of the mixture based on complete emulsiŽ cation would
have rendered different values.
This paper aims to test different methods for reducing the viscosity of heavy crude
for the purpose of facilitating its pipeline transportation, to test the stability of emulsions
in the presence of different oil contents, and to test the suitability of the double-log model
for predicting the effect of temperature on the viscosity of the crude and its mixtures.
Experimental Procedure
EmulsiŽ cation Procedure
The crude oil sample supplied to our laboratory contained a large amount of water.
Therefore the oil was poured in large beakers, covered with aluminum foil, wrapped
with plastic bags, and left for two days to allow the water to settle to the bottom.
Then the oil required for each experiment was scooped from the beakers. Tab water
was used to make the emulsions. A nonionic emulsiŽ er called Emulgen 120 (Polyoxyethylene(13.3)laury l ether) was used to stabilize the emulsions. In general nonionic
emulsiŽ ers are desirable in preparing emulsions because they are not affected by the
salinity of the water used, they are relatively cheap, and they do not produce any undesirable organic residue that can affect the oil properties. Emulsions were prepared by
the agent-in-water method (the emulsiŽ er was dissolved in water). The surfactant concentration (v v) is based on the total volume of the mixture. For each experiment, the
speciŽ ed amount of surfactant was dissolved in water by stirring with a magnetic stirrer.
The required amount of oil was preheated to 85° C in a water bath to improve its  uidity
and handling. Then the required amount of water, kerosene, or light crude was added to
the heated oil and the mixture was sheared at 6000 rpm for 3 min using a laboratory
high-speed mixer.
Determination of Emulsions Apparent Dynamic Viscosity
The apparent dynamic viscosity of freshly prepared emulsions or heavy crude/diluent mixtures was determined at different temperatures using a Haake coaxial-cylinder viscometer
(M10). The viscometer was connected to a TECHNE RB-12 heating/refrigerating bath
and circulator to control the temperature of the mixtures inside the viscometer’s cylinder.
The sensor type was determined in accordance with the dynamic viscosity of the mixture
to be tested.
Heavy Crude Oil Viscosity Reduction
95
Measuring the Stability of Prepared Emulsions
To check the stability of emulsions, 100 mL of each emulsion was placed in glass tubes
with 0.1 mL graduation. The tubes were stoppered tightly and left at room temperature
for 3 weeks. A stability inspection was carried out every 24 h.
Results and Discussion
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The Viscosity Behavior of Heated Heavy Crude Oil
The high viscosity of heavy crudes is attributable to (1) their high molecular weight
components, which become entangled and aggregated at low temperature and (2) the
formation of ordered structures in the liquid phase (Khan, 1996). Heating heavy crude
oils destroys the ordered structures in the liquid phase and reduces the viscosity. Figure 1
illustrates the effect of temperature on the crude oil under investigation. One can see that
the oil behaves as a fairly Newtonian  uid, becoming more pronounced as the temperature
increases. It can also be seen that the temperature has a dramatic effect on the crude oil
viscosity. Heating the crude from 20 to 25° C, for example, reduces the viscosity from
approximately 15000 to 11000 mPas, while heating it to 50° C reduces its viscosity to
< 1300 mPas. Our aim is to reduce the crude’s viscosity to a level below 500 mPas at
a temperature not exceeding 50° C. From the results shown in Figure 1 it is obvious that
heating alone is not sufŽ cient; therefore other methods need to be considered.
Viscosity Behavior of Oil/Water Emulsions
(a) Effect of Oil Content on Stability. To test the stability, emulsions containing 75%
oil were prepared in the presence of 0.5%, 1%, and 2% surfactant. It was noticed that
the emulsion prepared in the presence of 0.5% surfactant was not stable and there was
approximately 2% of water that separated after 3 weeks. However, emulsions prepared in
the presence of 1% or 2% surfactant were stable, and there was no water separation that
could be observed even after 3 weeks. Since the two amounts of surfactant produce similar
stability, it is more economical to prepare emulsions with the lower amount (i.e., 1%).
Figure 1. Effect of temperature on the viscosity of heavy crude oil.
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B. M. Yaghi and A. Al-Bemani
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Therefore the effect of an emulsion’s oil content on its stability was investigated in the
presence of 1% surfactant. Oil volume was varied from 40 to 80% with respect to the
total volume of emulsion. Varying the oil content of the emulsion to 80%, 75%, 73%,
and 70% produced no water separation. However, with the oil content being 60% and
50%, water separation occurred after 2 days, and after 3 weeks it reached 6% and 30%,
respectively. When the oil concentration was reduced in the emulsion to 40%, water
separation occurred instantly.
(b) Effect of Surfactant on Emulsion Viscosity. An emulsion is thermodynamically unstable because one phase is dispersed in another with an increase in the free energy of the
system. The emulsion tends to reduce the increase in free energy by inducing coalescence
of oil droplets (Khan, 1996). Therefore an emulsiŽ er is usually introduced to the system,
stabilizing the small droplets so that they do not coalesce and form large droplets or separate out as a bulk phase. Attempts were made here to prepare emulsions in the absence of
surfactants, but the emulsiŽ cation process was impossible. Al-Asmi et al. (1997) studied
the  ow behavior in pipelines of the same crude oil and its emulsions in the absence
of surfactants. They found that during the actual pumping of crude-water mixtures or
after a settling period, emulsiŽ cation was not possible even when the temperature was
increased to 40° C; as a result, the  ow in pipelines of emulsions with 50% oil content
was stratiŽ ed, with an upper region containing oil alone and moving at a lower velocity
and a lower region containing clear water moving at a faster rate. Additionally, they
observed that there was no pipeline circulation of emulsions containing more than 50%
oil content. It can be concluded that viscosity reduction is not achievable by the addition
of water without the process of emulsiŽ cation. Therefore surfactants are essential for the
preparation of uniform emulsions if pipeline transportation and the right viscosity levels
are desired. To investigate the effect of surfactant concentration on the viscosity of the
oil, emulsions with 75% oil were prepared in the presence of different surfactant concentrations. The viscosity measurements were taken at different temperatures. Figure 2
shows the viscosity of emulsions in the presence of different surfactant concentrations at
30° C. The Ž gure illustrates that emulsion viscosity increases as surfactant concentration
Figure 2. Viscosity of heavy crude oil-in-water emulsions (75:25) with different surfactant concentrations at 30° C.
Heavy Crude Oil Viscosity Reduction
97
increases, which is due to better emulsiŽ cation of the mixture. At higher temperatures,
viscosity differences become less pronounced (data not shown).
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(c) Effect of Oil Contents on Viscosity. Figures 3a and b show the viscosity behavior of
emulsions at different crude oil fractions and at 30 and 50° C. The behavior of the pure
crude changes from fairly Newtonian to shear thinning in the presence of up to 70%
oil content. At a ratio of 80:20 crude to water, the emulsion’s viscosity reaches higher
levels than that of pure crude oil in the low shear rate range, but becomes less in the
high shear rate range. Also, the Ž gure shows that viscosity decreases dramatically when
oil content decreases to 60%, although the emulsion is not stable. The viscosity of the
emulsion with 70% oil content at 30° C is about 400 mPas at a low shear rate (11 l/s)
but drops to 130 mPas at a high shear rate (1170 l/s). If the emulsion is heated to 50° C,
the viscosity drops to 300 mPas at a low shear rate and to 130 mPas at a high shear rate.
Figure 3. Viscosity of oil/water emulsions at different shear rates at (a) 30° C and (b) 50° C.
98
B. M. Yaghi and A. Al-Bemani
It can be seen from this Ž gure that the optimum amount of oil content in the high shear
rate range is 70%; the addition of higher amounts of oil gives viscous emulsions, while
the addition of smaller amounts results in the formation of unstable emulsions.
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Viscosity Behavior of Heavy Crude Oil in the Presence of Light Crude
Dilution of heavy crude was also carried out with different fractions of a light crude
that was obtained from a nearby Ž eld and that has a viscosity of 64 mPas and a speciŽ c
gravity of 0.88 g/mL at 30° C. The viscosity behavior of mixtures at 30° C and 50° C are
shown in Figures 4a and b.
Figure 4a shows that the mixture of light and heavy crudes behaves as non-Newtonian
up to 27% (v v) of the light crude but as a Newtonian  uid at 30% light crude. However,
at 50° C the mixture behaves as a Newtonian  uid at all the fractions studied. Mixing the
heavy crude with 15% light crude at 30° C drops the heavy crude viscosity to almost one
Figure 4. Viscosity behavior of heavy crude diluted with light crude at different shear rates and
at (a) 30° C and (b) 50° C.
Heavy Crude Oil Viscosity Reduction
99
half of its original value, while the addition of 30% light crude drops the viscosity to
approximately 1000 mPas. This reduction is still not adequate for pipeline transportation.
More light crude is needed to reduce the viscosity to a more practical level, but this
implies that expensive oil is needed for the transportation of a cheap one. In Figure 4b
we can also see that the viscosity can be reduced to 300 mPas, a more transportationpractical level, if the 30:70 mixture is heated to 50° C.
Viscosity Behavior of Heavy Crude Oil in the Presence of Kerosene
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Viscosity behavior of the heavy crude diluted with different fractions of kerosene is shown
in Figures 5a and b. It can be clearly seen that the addition of 10% kerosene is capable
of making drastic viscosity reduction. Better still is the addition of 20% kerosene to the
heavy crude because it reduces the viscosity to about 250 mPas. Heating the mixture
Figure 5. Viscosity behavior of heavy crude diluted with kerosene at (a) 30° C and (b) 50° C.
100
B. M. Yaghi and A. Al-Bemani
to 50° C achieves the same viscosity reduction but with the addition of 15% kerosene
instead of 20%. The problem with this method of reduction is that kerosene is expensive
and the use of 20% of it at 30° C may not be economical. A considerable proportion of
kerosene is needed even after heating the crude to a temperature as high as 50° C.
Viscosity Modeling of the Crude Oil/Water Emulsions and Mixtures
It is well known that temperature can cause viscosity to decrease. The rate of viscosity
change due to a change in temperature depends on the type of crude. The ASTM doublelog model is known to be suitable over a range of viscosity (g ) from 1 to 800,000 mPas
(Mehrota, 1990):
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log(log(g )) 5
a * log(T ) 1
b.
The double-log of the measured viscosities of oil/water emulsion and oil/diluent mixtures
were plotted against the log of temperature. Straight lines were obtained for all heavy
crude oil fractions and for all diluent fractions used. The parameters “a” and “b” appear
to be dependent on the heavy oil fraction in the case of emulsions and on the diluent
fraction in the case of mixtures. A single double-log model that Ž ts the viscosity data of
both emulsions and heavy crude/diluent mixtures was not attainable without large errors.
Therefore two separate models were obtained: one that Ž ts the viscosity of emulsions
and another that Ž ts the viscosity of heavy crude diluted with kerosene and with light
crude. The model that best Ž ts the viscosity data of the emulsions is
log(log(g )) 2
(0.4605* } 2
0.3747) log(T ) 1
b;
where } is the oil fraction.
The value for parameter “b” varies from 1.136 to 0.190 depending on the fraction
of heavy oil. Using this model to calculate the viscosity data results in an average error
of 7.2%, with a maximum error of 10% and a minimum error of 1%. Figure 6 shows the
experimental and the model-calculated viscosity.
Figure 6. Experimental and ASTM double-log model viscosities.
Heavy Crude Oil Viscosity Reduction
101
The viscosity data obtained from diluting the heavy crude with kerosene and with
light crude oil are both Ž tted by the following model:
log(log(g )) 5
(0.0402 * } 2
0.4248) log(T ) 1
b
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The values of parameter “b” for dilution with kerosene ranges from 0.9350 to 1.2135.
The average percentage of error is 9.4%, while the maximum is 12% and the minimum
is 0.35%. The values of parameter “b” obtained from dilution with light crude oil ranges
from 1.0940 to 1.2135. The average percentage of error is 8.4%, the maximum is 14%,
and the minimum is 1.5%. Figures (7a and b) show experimental and the model-calculated
viscosities.
Figure 7. Experimental and ASTM double-log model viscosities after dilution with (a) light crude
oil and (b) kerosene.
102
B. M. Yaghi and A. Al-Bemani
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Conclusion
Considering the viscosity levels obtained from oil/water emulsions, it has been shown
that the optimum amount of oil content is 70% at 30° C. Similar viscosity levels to those
obtained at the optimum amount of oil content in the emulsion can be achieved by
diluting with 25–30% light crude and heating to 50° C. Diluting with 20% kerosene at
30° C reduces viscosity to < 300 mPas, and if the mixture is heated to 50° C, the required
amount of kerosene can be reduced to about 15%.
The use of kerosene as a diluent is an expensive choice since approximately 20%
of it is required to reduce the viscosity of heavy crude to a desirable level. Dilution
with light crude requires the use of substantial amounts of expensive crudes in addition
to heating to high temperatures. However, reduction of the heavy crude’s viscosity by
the formation of emulsions that contain between 25 and 30% water is a more likely
approach since water is cheaper than either light crude or kerosene and the surfactant
used to stabilize the emulsion is also cheap. In addition to that, the emulsion does not
need to be broken down at the Ž nal destination if the oil is to be used to fuel power
plants.
References
Al-Asmi, K., M. Benayoune, and L. Khezzar. 1997. Flow behavior of heavy-crude water mixtures.
Petroleum Science and Technology 15:647–665.
Hardy, W. A., S. P. Sit, and A. Stockwell. 1988. Field trials of transoil technology for emulsion
pipelining of bitumen. Fourth UNITAR/UNDP Conference on Heavy Crude Tar Sands, Vol. 5,
Paper No. 222, UNITAR/UNDP: Edmonton, Alberta.
Khan, M. R. 1996. Rheological properties of heavy oils and heavy oil emulsions. Energy Sources
18:385.
Mehrota, A. K. 1990. Modelling the effect of temperature, pressure, and composition on the
viscosity of crude oil mixtures. Ind. Eng. Chem. 29:1574.
Shikoku Research Institute. 1999. Personal communication. 2109 Yashimanishimachi Takamatusu
KAGAWA, 761-0192, Japan.
Urdahl, O., A. O. Fredheim, and K.-R. Loken. 1997. Viscosity measurements of water-in-oil emulsions under  owing conditions: A theoretical and practical approach. Colloids and Surfaces,
123–124:623.
Zaki, N. N. 1997. Surfactant stabilized crude oil-in-water emulsions for pipeline transportation of
viscous crude oils. Colloids and Surfaces, 125:19.
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