Asphalt Ines
Transcript of Asphalt Ines
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Origin and Behaviour of Oil Asphaltenes –
Integration of Disciplines
Artur Stankiewicz
Society of Petroleum Engineers
Distinguished Lecturer Programwww.spe.org/dl
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Acknowledgments
The data and supporting examples are primarily based on
the research and field application that took place 1998-
2009 at various Shell locations.
Author is grateful to Shell and Schlumberger for
permission of presenting this material to the SPE
audience.
Cooperating service companies, scientific institutions and
all who, over the years, worked with me on the R&D and
implementation of technologies in the area of
asphaltenes.
• Introduction into the World of Asphaltenes
– Setting the scene
– Basic facts and definitions
– Origin of asphaltenes (source and changes in geological time)
– Few remarks on asphaltene structure & analytical techniques
– Theory of the oils “critical range”
• Fluid properties and live oil behaviour
– Stock tank liquid screens
– Live oil behaviour and “screens”
– Examples of diversity in the world of asphaltenes and implications
– Field application
• Conclusions
Outline
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Asphaltenes – why do we care?
• Asphaltenes precipitated in the production system
(reservoir – wellbore – tubing – pipeline – topside
facilities) may lead to their deposition =
reduced or shut-in production
Topside facilities
Pipes blocked due to asphaltenes
(photo courtesy of Nalco)
Asphaltenes – one of many solid phases
encountered in production systems
0
2000
4000
6000
8000
10000
12000
14000
16000
0 10 38 65 93 121
Temperature (°C)
Pre
ssure
(p
sia
)
Hydrate
Asphaltenes
Wax
• Asphaltenes
• Waxes
• Hydrates
• Diamondoids
• Inorganic Scales
• Sulfur
Asphaltenes when
unstable typically
precipitate at higher T
and P than other solids
Reservoir
Flow line
7After John Ratulowski
Asphaltenes deposition – how?
• Composition Changes
Instability due to commingling of incompatible fluids
Carryover & blending with LNG fouls gas side
equipment
Gas lift mandrills foul
Injection gas can cause reservoir impairment,
wellbore deposition, and fouling of pumps
• Pressure Changes
Near-perforation reservoir impairment
Deposits in wellbores & flowlines cause excessive
pressure drop & additional plugging
Precipitated solids accumulate in low energy regions
IMPLICATIONS:
It is a solubility class = NOT well defined molecule
Various analytical procedures prevent standardization
ASPHALTENES are defined as
„the material that precipitates out of crude oil or reservoir
rock extract on the addition of excess light alkanes‟
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0
1
2
3
4
5
Pentane Heptane Decane
Precipitant type
Asphaltenes
in Oil [wt. %]
Asphaltenes %
Cn of n-alkane
Asphaltene Content of „Unstable Oils‟
0.5 - 5
1 - 9
0.4
0.2
0.5-2
2 - 5
0.9 - 3.5
0.1 - 4.2
4 - 15
0.9 - 1.9
7 - 9
0.3
~0.8
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• Asphaltene problems are localized, <1% of total world production
• Some countries have serious challenges (e.g., Venezuela, Kuwait)
Asphaltenes – an Engineering Domain,
but… “Can‟t we just all get along?”
Main Technical Areas:
• Prediction (Deposition Potential)
• Prevention (Monitoring & Control)
• Remediation (Recovery & Removal)
• Inhibition (Chemical treatment)
Geochemistry brings a fresh view on nature‟s diversity –
„a global asphaltene molecule does NOT exist‟
influenced by source rock type and oil
generation/expulsion/migration processes.
Majority of issues are driven by fluids phase behaviour,
production scenarios, topside separation or the Enhanced
Oil Recovery processes.
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Simple solubility model can explain asphaltene stability
Asphaltene
Aromatic
Resin
Saturate S
A
R
A
„Geochemical and Engineering-View‟ on
Asphaltenes
12
HN
SSOH
S
NH
S
OH
0H
Modified from Pelet et al., 1986
After Steve Larter & Eugene Frolov
NRG Petroleum Group
Source Rock
Kerogen
Composition Thermal Maturity(t & T)
Secondary
Processes (in reservoir)
Biodegradation(bacteria)
Hybridization(mixing)
Gas Washing(late gas charge)
Oil CompositionAsphaltene Content/Stability
Natural Processes that can Affect
Asphaltene Stability in Crude Oil
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Marine deltaic and open
marine settings
Type II
Flood Plain CoalsType IIILacustrine Shales
Lagoonal shales and coals
Type I
Where They Come From? – Source Rock
Kerogen Types and Origin
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Maturity and its Importance
• “A rock with sufficient organic matter
of suitable chemical composition to
generate and expel hydrocarbons
at appropriate maturity levels
is called a source rock”
• Thermal degradation of kerogen
(burial, T )
→ breakdown and release of hydrocarbons
• Maturity = structural simplification
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Origin and Maturity Affects Structure and
Behaviour (T, from bio- to geomacromolecule)
0N
0
H0
N
0
0
0
0
N
0H
H0
S
S
HS
0H
H0
H0
0
0
0
0
0
0
H0
0H
N N
N NV-0
0
H00
N
0
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0N
0
H0
N
0
0
0
0
N
0H
H0
S
S
HS
0H
H0
H0
0
0
0
0
0
0
H0
0H
N N
N NV-0
0
H00
N
0
N
H0
N
N
H0
S
S
H0
0
S
N
HS
N
N
With maturity (irrespective of their source origin):
Molecular ratios H/C, O/C, N/C and S/C
Molecular weight (size)
Metals (e.g., Ni, V)
Sulfur %
Asphaltenes – General Trends
IMPLICATION:
Oils in the specific “maturity range” show increased
potential for asphaltene precipitation – low maturity, heavy
and biodegraded oils, and high maturity condensates
are generally stable 17
Pitch Lake Trinidad
GOM
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
15 20 25 30 35 40 45 50
Oil Gravity [API]
Oil
Asphaltene C
onte
nt
[wt.
%]
West Africa
Venezuela
North Sea
Italy
Canada
Primary fluids onlyApprox. Region of
Fluids with Asphaltene
Problems
Middle East
Oil Asphaltene Content and the Oil Gravity
as Indicators of Maturity
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Maturity Controlling Fluid Stability thus
Asphaltene Precipitation – Hypothesis
Maturity increase
Maturity indicators: e.g. API increase, Asphaltene % decrease
Flu
id In
sta
bil
ity w
rt
Asp
halt
en
e P
recip
itati
on
Low Maturity
Fluids(Heavier)
High Maturity Fluids(Condensates)
Critical Range
NOTE: Natural processes
and production scenarios
can affect asphaltenes
behaviour
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Compositional Asphaltene Stability Screens
Stable
Unstable
Marginal
Asphaltene / Resin
Sa
tura
te / A
rom
atic
Unstable
Stable
20Stankiewicz et al., 2002
• Colloidal instability index
• Critical asphaltene to resin ratio
• SARA plot (shown)
Dead Oil Titration Tests
Neat Oil Oil + 1 ml of
Hexadecane P = 1.5
P-Value
2 mWNIR
Laser
Detector
Titrator
TC
Magnetic Stirrer
Volume of Titrant
Floc Point
Computer
Tra
nsm
itt e
dP
ow
er
FPA – Floc Point Analyzer
Heptane
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Discrete or continuous titration
Detection
• Visual
• Spot test
• Light scattering
Does not contain effect of gas
Stable Unstable
High p&T System to Evaluate Asphaltene
Behaviour in Live Oil
22DBR Solids Detection System (Light Transmittance)
Neat oil
Oil with asphaltenes
Example of „Non-problematic‟ Fluid from
Venezuelan Well
0 2000 4000 6000 8000 10000
Pressure (psig)
Power of Transmitted Light (mW)
Water-like Droplets
Water-like Droplets
Pres
PSAT
~ 1930 psi
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Non-problematic = no deposition observed
Problematic = deposition in the wellbore observed
Example of „Problematic‟ Fluid from
Venezuelan Well
0 2000 4000 6000 8000 10000
Pressure (psig)
Power of Transmitted Light (mW)
Pres
10mm
10mm10mm
10mm
10mm
PSAT ~ 1860 psi
POAP ~ 3500 psi
Information that can be used to optimize operations 24
Example of Variation in Molecular
Composition of Asphaltenes
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
0.00 0.01 0.02 0.03 0.04 0.05S/C
H/C
of A
sphaltenes
VEN
NS
GOM
World
MW~1000
MW~2200
MW~3500
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MW based on GPC (SEC)
0200400600800
1000
0 10 20 30 40 50 60 70 80 90 100
020406080
100
0200400600800
1000
0 10 20 30 40 50 60 70 80 90 100
020406080
100
020406080
100
020406080
100
020406080
100
Part
icle
Co
un
t
Size [mm]
Venezuelan Oil
(deposition problems)
North Sea Oil
(no deposition observed)
9000 psi
5250 psi
3500 psi
9000 psi
5000 psi
4500 psi
3500 psi
0200400600800
1000
5000 psi
Variations in Flocc Size is Critical
0-60 0-15
26Depressurization experiments at reservoir T
Oil/Asphaltene Molecular Composition vs
Activity of Field Chemicals
CB DA
Different Chemical Inhibitors North Sea OilAsphaltene = 1 %
API° = 38.5
Sulfuroil = 0.11 %
Venezuelan OilAsphaltenes = 5 %
API° = 32
Sulfuroil = 1.4 %
27The same chemical react differently with different asphaltenes
“Venezuela” type asphaltenes “North Sea” type asphaltenes
After: Ting et al, Petrophase Trondheim, 2004
Variations in PVT Behavior
10 38 65 93 121 1490
2000
4000
6000
8000
10000
Pre
ssu
re (
psia
)
Temperature (°C)
L & V
Liquid Phase
L & V
L & V & Asph Phases
L & Asph Phases
Liquid Phase
L &
Asph &
Wax
Phases
10 38 65 93 121 149
0
2000
4000
6000
8000
10000
Temperature (°C)
12000
Regions of asphaltenes instability
L & Asph Phases
L & V & Asph Phases
L &
Asph &
Wax
Phases
Asph Stability
Bubble point
Asph Stability
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Example of Carbonate Reservoir
160
00
5000 meters
N
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22.2
26
28.7
31.8
API31
29.4
28.5
28.6
30.6
2928.5
28.3
29.5
1.7
2.34
2.13
2.01
1.54
S% 1.83
1.78
1.72
1.73
1.8
1.811.9
1.99
1.83
5.6
11.2
13.1
8.8
4.3
Asphaltene Content 6.0
7.9
7.9
7.8
6.5
7.27.8
7.0
6.7
1
1
1
2
3
2
2
2
3
3
4
3
4“Problem” ranking
1 – Heavy deposition
4 – No deposition
Lighter fluids with
asphaltene
challenges
„Heavier‟ fluids
without asphaltene
deposition
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• Molecular composition of asphaltenes varies and depends
on factors such as source rocks and maturity
– an “average” asphaltene structure does not exist.
• Knowledge of physical/chemical properties of oil and its
asphaltenes may be successfully used for prediction of their
behavior ahead of production – best practices:
– Routine measurements of fluid property for each new well or
reservoir
– Comprehensive database of fluid properties for each field (existing
and new)
– Constant calibration of empirical observations against field
experience
– Integrated approach and cooperation of various disciplines
Conclusions
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„Food for thought‟
• Asphaltene deposition problems to date are confined to
specific areas and relatively light fluids, however:
– Increased focus on the EOR/IOR unravels new potential
challenges in the area of precipitation/deposition of
previously “stable” hydrocarbon fluids.
• An integrated approach and cooperation of engineers and
geoscientists (e.g. geochemists) is necessary to
understand oil asphaltene behavior and its influence on
fluid properties.
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