asphaltenes newmexicotech2000
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Asphaltene: A General Introduction
Jianxin Wang
P & Sc GroupPRRC, New Mexico Tech
Oct. 18, 2000
Outline
What is asphaltene?
Why to study asphaltene?
How to characterize asphaltene stability in crude oil?
Asphaltenes are the most heavy and polar components in crude oil
Crude oil
Saturates ResinsAromatics Asphaltenes
S A R A
nonpolar molecular weight, polarity & aromaticity
(0-20%)
Separating asphaltene from crude oil
ASTM D2007-80:
Mixing crude oil / n-C7 (or n-C5) = 1 / 40Aging for two daysFiltering through 0.22 µµm filter paper
Separated asphaltene amount is determined by precipitant molecule size
2 4 6 8 10 120
10
20
30
40
50A
sph.
(w
t%)
Chain-length of n-alkane precipitant
Separated asphaltene amount is also determined by precipitant/oil ratio
2 5 10 20 50 100 200 5000
1
2
3
4
5
6
7
8A
sph.
(w
t%)
n-C7 / oil ratio
Mars-pink
Furthermore, separated asphaltene amount is also time-dependent
1 2 5 10 20 50 100 2004.2
4.4
4.6
4.8
5
5.2
5.4
5.6
5.8A
sph.
(w
t%)
Aging time (days)
Mars-pink/nC7=1/10
Asphaltene is a compositional continuum
Long, R.B.: "The Concept of Asphaltenes," Chemistry of Asphaltenes, J.W. Bunger and N.C. Li (eds.), ACS, Washington, DC (1981) 17-27.
polarity = N, S, O
aromaticity =
Polarity & aromaticity
Mol
ecul
ar w
eigh
t
n-C7 asph.
n-C5 asph.
Typical asphaltene molecular properties
H/C = 0.8 - 1.4
Molecular weight: depends on solvent and concentration monomer = 500 - 1000 micelles = 1000 - 5000
Heteroatoms: acting as polar functional group S=0.5-10 wt%; N=0.6-2.6 wt%; O=0.3-4.8 wt%
Metal elements: Ni, V, Fe
Hypothetical polycyclic structures for asphaltene molecules
Speight, J.G.: "A Chemical and Physical Explanation of Incompatibility during Refining Operations," Proc. 4th Intl. Conf. on the Stability and Handling of Liquid Fuels, US Dept. Energy, 169 (1992).
N S
S
S
OH
SN
S
N
O
Asphaltene?Like a sea monster
Differences between asphaltene and wax
Asphaltene Wax
Dissolves in heptane:
Crystalline:
Melting point:
No Yes
No Yes
No Yes
Buckley, J.S.: "Asphaltenes: Separating Fact from Fiction," SPE Distinguished Lecture Slides (1998-99).
Outline
What is asphaltene?
Why to study asphaltene?
How to characterize asphaltene stability in crude oil?
What if asphaltene flocculates ?
plugging reservoir
foulingproduction facilities
alteringwettability
poisoning refinary catalysts
AsphalteneFlocculation
Stability is determined by crude oil solvency
Temperature
Pressure
Composition - gas injection; - phase separation; - incompatible chemicals; - mixing of crude streams; - etc.Asphaltene
stability
High asphaltene content is not necessary to associate with high risk of trouble
Carbognani, L. and Espidel, J.: "Characterization of Solid Deposits from Production Facilities. Identification of Possible Causes of Deposits Formation," Vision Technologica,
Vol. 3, No. 1, 35-42.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
20
40
60
80
100
saturates
troublefree
aromatics
resins
asphaltenes
troublesomeW
eigh
t %
Oil # from Venezuela oil fields
Asphaltene trouble is associated with RI
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 191.40
1.45
1.50
1.55troublesome troublefree
Oil #
Low RI High RI
PRI
Buckley, J.S.: "Asphaltenes: Separating Fact from Fiction," SPE Distinguished Lecture Slides (1998-99).
RI
Outline
What is asphaltene?
Why to study asphaltene?
How to characterize asphaltene stability in crude oil?
For a given crude/precipitant, flocculation occurs at a critical RI
Volume fraction
crude oil
maltene
alkane flocculated
PRI
RI
onset
redissolved
stable
Buckley, J.S.: "Asphaltenes: Separating Fact from Fiction," SPE Distinguished Lecture Slides (1998-99).
Asphaltene stability varies with solvent RI
Buckley, J.S.: "Asphaltenes: Separating Fact from Fiction," SPE Distinguished Lecture Slides (1998-99).
In a "poor" solvent, asphaltenes attractive forces are enhanced.
In a "good" solvent, asphaltenes are not
strongly attracted to one another.
Low RI
High RI
RI measurement
RI accuracy = 0.0001T: 10 ~ 70 °C
GPR-11-37
n = 1sin(θθ)
total internal reflection
θθ
sample
Sodium-D light beam
refractometer
Procedure for onset detection
Prepare a series of mixtures with varying oil/precipitant ratios in sealed vialsAging for 24 hoursObserve asphaltene precipitation, if any, under microscopeOnce onset is detected, record volume ratio and measure the refractive index (RI) for mixture
Asphaltene flocculates under microscope (1)
3
21
Asphaltene flocculates under microscope (2)
PRI vs. time (Lagrave)
Time (day)0 2 4 6 8 10 12 14 16 18
1.44
1.45
1.46
1.47
1.48
1.49
1.50
n-C5
n-C9
n-C15
particle onset aggregate onset
PRI
Volume ratios of precipitant to oil at onset
4 6 8 10 12 14 160
1
2
3
4
Chain-length of n-alkane
Vpr
ecip
itan
t / V
oil
(ml/m
l)
A-95 Lagrave
Mars-pink Tensleep
Lost Hills
A-93
RI at onset (PRI) for crude oils
4 6 8 10 12 14 161.40
1.42
1.44
1.46
1.48
1.50
1.52
PRI
Chain-length of n-alkane
A-95 Lagrave
Mars-pink Tensleep
Lost Hills
A-93
Simple correlation of PRI vs. precipitant
10 11 12 13 14 15 16 171.40
1.42
1.44
1.46
1.48
1.50
1.52
vp
Crude oils
PRI
average r = 0.992
A-95 Lagrave
Mars-pink Tensleep
Lost Hills
A-93
Conclusions
Asphaltene molecules are polyaromatics with side chains. They exist in crude oils as monomer and micelles equilibrated to each other. The sizes of asphaltene micelles fall in colloidal range.
Asphaltene flocculation occurs when oil solvency is reduced. Flocculated asphaltene could have detrimental effects on oil production, transportation and refinary process.
Refractive index (RI) is a simple, readily measurable parameter for characterizing crude oil solvency with respect to asphaltene stability.
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