Primary funding is provided by

The SPE Foundation through member donations

and a contribution from Offshore Europe

The Society is grateful to those companies that allow their

professionals to serve as lecturers

Additional support provided by AIME

Society of Petroleum Engineers

Distinguished Lecturer Programwww.spe.org/dl

2

Origin and Behaviour of Oil Asphaltenes –

Integration of Disciplines

Artur Stankiewicz

Society of Petroleum Engineers

Distinguished Lecturer Programwww.spe.org/dl

4

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

5

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‟

9

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

10

• 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.

11

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

13

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

14

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

15

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

16

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

18

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

19

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

21

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

23

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

25

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

28

Example of Carbonate Reservoir

160

00

5000 meters

N

31

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

29

• 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

30

„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.

31