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Fundamental Chemistry of Heavy Crude Oils

Sbastien SIMON, Johan SJBLOM

Ugelstad Laboratory, NTNU, Trondheim, Norway

Tekna, Stavanger , September 25th 2013

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Goal

Briefly describe evolution of composition of crude oils from light to heavy

Do we have more flow assurance problems with heavy crude oil? Asphaltene precipitation

Oil/water separation

Calcium naphthenate deposits

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Bulk Properties are Ruled by API

Co-variance of important bulk properties

Hannisdal et al.,

2007

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Composition: SARA Separation based on polarity and solubility of crude oil components Separation in 4 fractions

Increasing polarity

Crude oil

Saturates Aromatics Resins Asphaltenes

Heavy

crude

A S R A

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Asphaltenes Most polar molecules of crude oil Soluble in toluene, insoluble in n-alkanes

Strongly aromatics

Contains heteroatoms and metals

Average M750 g.mol-1

Self-associate in model systems and oils

Murgich,

2003

The continental model The archipelago model

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Asphaltene model compounds

Nordgrd and

Sjblom, 2008

Modulable

head group

Molecular

weight 700

g.mol-1

Polyaromatic core +

protruding alkane chains

Model molecules having similar functionalities of asphaltenes Obtaining a better understanding of emulsion formation, fouling and deposition

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Difference Resins/Asphaltenes

Primary difference: solubility in n-alkane Resins less aromatics

Contain most of acids and bases

Do not (or little) self-associate in model systems and oils

Important to keep asphaltenes dissolved in oil

Pfeiffer,

1940

Aphaltene

Resin

Preponderantly aromatic

Mixed aromatic- naphthenic nature

Mixed naphthenic-aliphatic nature

Aliphatic

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Evolution SARA with API More and more polar molecules Ex. for Athabasca crude oil

Koots and Speight,

1975

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Asphaltene Precipitation

Can lead to deposition and fouling

The asphaltene precipitation can happen: During the depressurization of crude oil

If the composition of crude oil changes or another component is mixed with

crude oil

Ex: Asphaltene Precipitation due to mixing with condensate from gas

compressor station

Courtesy of Hans

Oschmann,

Champion Tech./

NTNU

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Precipitation Risk vs API % asphaltenes increases with API Are precipitation risks higher for heavy crude oils?

Reply with the de Boer plot

From the de Boer plot, less risk with heavy crude oil

More problem with light crudes already noticed by de Boer et al.

Yonebayashi et al.

2013

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Precipitation Risk vs API Diagram proposed by Stankiewicz et al. (2002) Consistent with the peptization model by Pfeiffer et al. (1940)

Plot predict problem when the peptizing fraction content is low

No indication for more problems with heavy crude oils (low saturate content)

Yonebayashi et al.

2013

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New JIP at Ugelstad Laboratory Precipitation/deposition/fouling of asphaltenes Goal: Create knowledge and understanding needed for a reliable assessments of precipitation/deposition/fouling risks during oil production and transport

Starting early 2014

Contact: Prof. Johan Sjblom

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Amount quantified by TAN (Total Acid Number) measurements

Naphthenic acids CnH2n-ZO2 with z specifies a homologous series

Mostly part of resin fraction Some example of mono-acids

Acids Present in Crude Oils

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Heavy and extra heavy oils are acidic Main mechanism: Biodegradation increases the density (lower API) and synthesizes NA

TAN vs API

Katz and Robison,

2006

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Metabolization of paraffins first

Mechanism Biodegradation

Wenger et al.,

2002

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Biodegradation increases the TAN via NA formation

Evolution of NA with Biodegradation

Meredith et al.

2000

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Biodegradation increases complexity of NA composition Gas chromatogram of acid fraction

Evolution of NA with Biodegradation

Meredith et al.

2000

Retention time

Undegraded oil

(n-alkyl visible)

degraded oil +

degraded oil ++

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A Special Type of Naphthenic Acid: Arn

4 acid groups

C80, M=1230 g.mol-1

Responsible for the formation of calcium naphthenate deposit

Low concentration compared with Monoacids but big importance!

Methods developed by Ugelstad Laboratory to determine Arn content in deposits and crude

oils (ppm level)

Discovered by Statoil and ConocoPhillips in 2004

Lutnaes et al. 2006

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Trends with API List of fields where Arn has been detected in crude oil

Arn presents in very different oils, consistent with suspected archaea origin

Deposition seems to happen with very different crudes

Need more data to be more conclusive (sampling data, produced water data)

Field TAN

(mgKOH/g) API

Fields

deposit Ref

Tchibelli 0.66 36.5 No Brocart et al., 2007

Acacia 0.36 36 ? Brocart et al., 2007

Usan 3 0.58 35 ? Brocart et al., 2007

Offshore Nigerian field B 0.2 34 Yes Igwebueze et al., 2013

Ofon 0.4 34 No Brocart et al., 2007

Girassol 0.38 30.5 No Brocart et al., 2007

Blake 0.11 30 Yes Melvin et al., 2008

Offshore Nigerian field A 0.5-0.8 29 Yes Igwebueze et al., 2013

Heidrun 2.7 26 Yes Vindstad et al., 2002

Gimboa 0.65 25.3 Yes Junior et al., 2013

Afia 1 25 Yes Brocart et al., 2007

Kuito 2.15 20 Yes Brocart et al., 2007

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Bases Present in Crude Oil

Derivatives of pyridine and its benzologs (cores)

1Aksenov V.S. et al. Chemistry of Heterocyclic Compounds, 1979, 15, 119-135

N N N

N

Pyridine

pKa=5.25

Quinoline

pKa=4.90

3,4-benzoquinoline 7,8-benzoquinoline

No or very little amines

Amount of base quantified by TBN (Total Base Number) measurement

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Seems to be a loose correlation between density and TBN Generally higher TBN value for heavy crude oil

Evolution of TBN with Density

Data from

Simon et al., 2010

Eftekhardadkhah et

al., 2013

d at 50 C g.cm-3

0,75 0,80 0,85 0,90 0,95 1,00

TB

N m

g.g

-1

0

1

2

3

4

5

6

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Oil/Water Separation JIP program at Ugelstad Laboratory to determine parameters

responsible for emulsion stability

30 crude oils

Composition

Bulk and Interfacial Properties

Stability determined by the Ecrit method

Correlations

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Multivariate Data Analysis Co-variance of several properties/composition parameters (slide 3)

Stability of emulsions can be well-fitted with viscosity alone Comparison experimental and semi-theoretical destabilization time

Silset et al.

2010

More research to find effect of other properties/composition parameters

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Conclusion

Complexity of chemistry increases with oil density

Do we have more flow assurance problems with heavy crude oil? Oil/water separation: Yes

Asphaltene precipitation: No

Calcium naphthenate deposition: Need more data to be conclusive

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Acknowledgments to our Sponsors (Emulsion and Naphthenate Programs)

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Back Slides

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Classification of crude oil with density

Density linked to API gravity

o

o

141.5API= -131.5

Sp.gr@15 C

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Crude Oil Matrix Tested at Ugelstad Lab

Hemmingsen et al. 2005