Comparison of Correlations Based On API Gravity For Predicting Viscosity of Crude Oils PDF
Comparison of Correlations Based On API Gravity For Predicting Viscosity of Crude Oils PDF
Comparison of Correlations Based On API Gravity For Predicting Viscosity of Crude Oils PDF
Fuel
journal homepage: www.elsevier.com/locate/fuel
h i g h l i g h t s g r a p h i c a l a b s t r a c t
Comparison of available correlations %AAD value as a function of API gravity crude oil used in the validation analysis [Beggs (M), Glaso (h),
for predicting viscosity of crude oils. Kartoatmodjo (s), Hossain (e), Egbogah (N), Elsharkawy (j), Naseri (d), Alomair (), and this work (+)].
New correlation for viscosity
prediction is proposed.
High accuracy of proposed correlation
for heavy crude oil.
Two-coefficient correlation as a
function of API gravity and absolute
temperature.
a r t i c l e i n f o a b s t r a c t
Article history: Correlations for the prediction of dynamic viscosity of crude oils as a function of the absolute temperature
Received 24 January 2014 and API gravity are compared. Twelve crude oils with wide range of API gravity (12.4–43°API) are used for
Received in revised form 6 August 2014 comparison of correlations. It was identified the need of an accurate correlation for calculating viscosity
Accepted 7 August 2014
of heavy crude oils. Thus, a new correlation is proposed, which was validated using viscosity values dif-
Available online 24 August 2014
ferent to those used to derive it. Comparison of results using literature information and own set of data
indicated better predictability over other correlations previously reported. High accuracy was observed
Keywords:
with the developed correlation for crude oils with low API gravity (621.1°API), so that it resulted to be
Crude oil
Viscosity prediction
more accurate for calculating viscosity of heavy crude oils.
Correlation Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction accepted that a crude oil can be transported only if its kinematic
viscosity is lower than 250 cSt at 100 °F [1]. API gravity is also used
The viscosity is a property of great importance during petro- as an indicative of crude oil transportability, but there is not a pre-
leum characterization since its value defines the transportability cise specification of its value. In other words, for a crude oil to be
of crude oils through the pipelines. For instance, it is widely transported it is mandatory a prior reduction of its viscosity.
Nowadays, because of the increasing production of heavy and
⇑ Corresponding author. extra-heavy crude oils, their transportation from production facil-
E-mail address: jfsanchezm@ipn.mx (F. Sánchez-Minero). ities to distribution terminals or refineries has become a critical
http://dx.doi.org/10.1016/j.fuel.2014.08.022
0016-2361/Ó 2014 Elsevier Ltd. All rights reserved.
194 F. Sánchez-Minero et al. / Fuel 138 (2014) 193–199
Nomenclature
problem. For pipeline transportation, the most used technologies at 288.71 K and this value was used to calculate the API gravity.
are heating the crude oil pipeline or dilution with light crude oil For each test, 3 mL of sample were fed to the equipment.
[2–4]. However, these approaches are expensive. In addition, heat-
ing does not upgrade the properties of crude oil, and is not a viable
3. Results and discussion
method to transport over large distances. Dilution improves the
properties of heavy crude oil but at the expense of loss of diluent,
3.1. Description and analysis of correlations
making it necessary to find a cheap diluent near the production
wells. There are also other options, e.g. partial catalytic upgrading
The majority of correlations developed to predict the dynamic
[5,6], which requires higher investment costs. In any case, it is
viscosity of crude oil as a function of API gravity and temperature
indispensable to determine the viscosity of the crude oil to verify
are based on the logarithmic function. The most used correlations
if it accomplishes the desired specification for transportation.
have been proposed by Beal [7], Beggs and Robinson [9], Glaso [10],
Various standardized methods are available for experimental
Egbogah and Ng [11], Kartoatmodjo and Schmidt [15], Elsharkawy
determination of viscosity for different types of crude oils and
and Alikhan [17], Naseri et al. [18], Hossain et al. [19], Alomair et al.
petroleum products. The most used are ASTM D88, ASTM D445,
[20], and Petrosky and Farshad [21]. Table 1 presents these corre-
ASTM D2170, ASTM D7042, ASTM D7483 and ASTM E102. The
lations, the source of crude oil used in obtaining them, as well as
major differences among them are the type and required amount
the range of application in function of the API gravity. Some of
of sample, the experimental setup, the time for analysis, the
the equations exhibit similarities in the number of parameters
operating conditions of equipment, and the ranges of viscosity in
included (e.g. Egbogah and Elsharkawy) or in the mathematical
which the device can be used. In practice, it has been observed that
structure, such as Beggs and Robinson [9] and Egbogah [11]. More-
measuring the viscosity of crude oils with low API gravity is
over, Glaso [10] and Kartoatmodjo and Schmidt [15] coincide in
complicated due to their own nature and difficulty to handle. This
using the API gravity value raised to an exponent that depends
makes the analysis requires more time and greater amount of
on the temperature. However, the equations proposed by Kar-
sample to obtain reliable results.
toatmodjo and Schmidt [15], Hossain et al. [19], and Alomair
The viscosity of crude oil can also be predicted by means of
et al. [20] reach higher viscosity values, therefore are applicable
correlations. Several methods have been proposed to predict dead
for heavier crude oils.
oil viscosity (lod), saturated or bubble point viscosity (lob), and
Even though the authors of above correlations claim that accu-
under saturated oil viscosity (lo). Depending on the category, the
rate predictions can be obtained with their proposed equations, the
correlation uses parameters and properties such as API gravity,
correlation usually will not work for a crude oil with different API
temperature, pour point, pressure, bubble point pressure, gas/oil
gravity and temperature range from those that were used to
ratio, and molecular weight. According to this, two types of
develop it. In this sense, Fig. 1 illustrates the applicability interval
correlations for prediction of crude oil viscosity are reported in
for correlations included in Table 1. The equation proposed by Beal
the literature [7–21]: (1) those using conditions and bulk proper-
[7] is applicable for heavy crude oils with low API gravity (down to
ties such as temperature, pressure and specific gravity, and (2)
10°API) and consequently, with high viscosity (155 cP), however,
those using crude oil composition, normal boiling point, and pour
the correlations of Kartoatmodjo and Schmidt [15], Hossain et al.
point temperature. Additionally, viscosity can also be predicted
[19], and Alomair et al. [20] reach higher viscosity values (up to
by corresponding state and equation of state based methods.
586 cP, 451 cP, and 11360 cP, respectively). Other correlations as
All the authors reported high accuracy for viscosity prediction
Glaso [10], Elsharkawy and Alikhan [17], Naseri et al. [18], and Pet-
with their correlations, however, they were developed and tested
rosky and Farshad [21], cover relatively small viscosity and API
with a particular set of experimental data, and extrapolation to
gravity ranges.
other data may change the precision of predictions. Thus, the
aim of this work is to compare all the reported approaches and
to develop a new correlation to predict the dynamic viscosity for 3.2. Comparison of correlations
dead crude oils, by using experimental data of viscosity of crude
oils with API gravity ranging between 12.4° and 43°. The performance of described correlations was compared using
dynamic viscosity values of twelve crude oils with API gravity from
12.4 to 43°API (Table 2). The precision that presents each correla-
2. Experimental data tion was analyzed by means of the average absolute deviation
(%AAD), which is obtained using the following equation:
The dynamic viscosity and specific gravity of crude oils were 1X n
jlcal lexp j
obtained using a SVM 3000 Stabinger viscometer according to %AAD ¼ 100 ð1Þ
n i¼1 lexp
ASTM D7042 method. The dynamic viscosity for each crude oil
was measured at temperatures between 303.15 and 333.15 K at where n is the total number of experimental data, lexp the experi-
atmospheric pressure, whereas the specific gravity was obtained mental viscosity value, and lcal the predicted viscosity value.
F. Sánchez-Minero et al. / Fuel 138 (2014) 193–199 195
Table 1
Correlations to predict the dynamic viscosity of crude oils.
x
Petrosky and Farshad [21] lod ¼ 2:3511 107 T 2:10255
f ½logðAPIÞ 25–46 0.72–10.2 US
x ¼ 4:59388 logðT f Þ 22:82792
a
Not available.
Fig. 2. %AAD value as a function of API gravity crude oil using different correlations
Fig. 1. Range of applicability of API gravity for several correlations used to predict [Beggs (M), Glaso (h), Kartoatmodjo (s), Hossain (e), Egbogah (N), Elsharkawy (j),
viscosity. Naseri (d), and Alomair ()].
Table 2
Dynamic viscosity of crude oils with different API gravity.
API gravity 12.4 14.7 15.9 18.6 20.9 24.6 26.6 28.7 30.2 33.2 37.6 43.0
Temperature (K) Viscosity (cP)
303.15 17609.0 3731.2 1481.4 437.7 154.7 49.7 24.5 17.7 11.7 7.21 3.58 1.88
308.15 10255.0 2359.6 985.4 312.7 116.0 36.7 20.1 14.1 9.91 6.21 3.16 1.71
313.15 6192.2 1538.8 674.1 227.4 87.9 29.3 16.7 11.8 8.61 5.43 2.82 1.55
318.15 3869.6 1031.5 473.7 169.8 68.3 25.3 14.0 10.2 7.46 4.78 2.54 1.41
323.15 2478.7 710.7 341.3 128.2 53.8 22.7 11.9 8.90 6.56 4.24 2.30 1.29
328.15 1626.1 503.0 251.4 98.9 43.1 19.4 10.3 7.94 5.81 3.79 2.09 1.19
333.15 1100.8 366.1 188.9 77.9 35.1 17.3 8.89 6.95 5.18 3.40 1.90 1.10
196 F. Sánchez-Minero et al. / Fuel 138 (2014) 193–199
a correlations without considering that it may not be applicable to the API gravity of the crude oil is higher than 28.7°, Glaso [10]
the particular case. Fig. 2 confirms this fact. and Kartoatmodjo and Schmidt [15] correlations reached a greater
Then, for API gravity higher than 20°, which is from medium fit. Finally, the correlation of Naseri et al. [18] presented an
and light crude oils, some correlations tended to improve their increase in their accuracy when it was used for light crude oils,
accuracy. However, there was not a correlation that showed the whereas the correlations proposed by Beal [7] and Petrosky and
best fit for the entire studied region (12.4–43°API). Beggs and Farshad [21] were excluded from further analysis because they
Robinson [9], Egbogah and Ng [11] and Elsharkawy and Alikhan exhibited quite high deviations to predict the dynamic viscosity
[17] correlations presented a higher fit, although still poor; when with different crude oils.
the API gravity of the crude oil is lower than 28.7°. In contrast, if The above results indicate that most of the available correla-
tions fail in predicting the viscosity of heavy oils. Only a couple
of them succeed in the calculation of viscosity of crude oils with
API gravity higher than 26.6°. The same observation has been
recently derived when examining mixing rules for determination
of viscosity of petroleum blends, that is, they are not capable to
predict viscosity of heavy oil blends [4]. There is then a need to
establish new correlations that achieve more accurate prediction
of viscosity for heavy and extra-heavy crude oils.
Table 3
Dynamic viscosity of crude oils used for validation of the proposed correlation.
Fig. 5. %AAD value as a function of API gravity crude oil used in the validation
analysis [Beggs (M), Glaso (h), Kartoatmodjo (s), Hossain (e), Egbogah (N),
Fig. 4. (a and b) Coefficients of Eq. (4) as a function of API gravity crude oil. Elsharkawy (j), Naseri (d), Alomair (), and this work (+)].
F. Sánchez-Minero et al. / Fuel 138 (2014) 193–199 197
Fig. 6. Parity plots of experimental vs. calculated viscosity values for crude oils with (a) 13.3°API; (b) 15.5°API; (c) 21.1°API; (d) 29.8°API and (e) 38.3°API. [Glaso (h),
Kartoatmodjo (s), Hossain (e), Elsharkawy (j), Alomair (), and this work (+)].
Table 4
%AAD and SD values that present the different crude oils used in the validation analysis.
where lod is the dynamic viscosity in cP, T is the absolute temper- 3.4.2. Literature viscosity data
ature in Kelvin and, a and b are coefficients, which depend on API To confirm the above results, the information reported by
gravity. Barrufet and Setiadarma [25] for a heavy crude oil at different
Then, the experimental viscosity values of the crude oils men- temperatures (295.7–338.58 K) was used to estimate the viscosity
tioned before were used to obtain coefficients a and b from Eq. using all correlations; further, the %AAD values were obtained.
(4) for each crude oil. Excellent fit (R2 > 0.985) for both coefficients The experimental values of viscosity are reported in the last
was achieved as can be observed in Fig. 4. The resulting depen- column of Table 3. The lowest %AAD values were obtained for
dence of a and b with API gravity was: Beggs and Robinson [9], Hossain et al. [19], and the proposed
correlation (65.5, 62.7, and 62.3, respectively). It is important to
a ¼ 3:9 105 API3 4:0 103 API2 þ 0:1226 API 0:7626 ð5Þ mention that there is limited reliable information of crude oil
viscosity values in literature. Nevertheless, it can be observed that
the correlation developed in this work can be applied to predict the
b ¼ 9:1638 109 API1:3257 ð6Þ
viscosity of heavy crude oils, more precisely when the API gravity
is lower than 21.1°.
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