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HEavy oil
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U g e l s t a d L a b o r a t o r y
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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