Wind Speed (m/s

Weathering properties at sea of the
Fray crude, Lillefrigg condensate
and the
I[NO:
7525 blend of these products
Final version
Per Johan Brandvik
Tove Strarm-Kristiansen
Per S. Daling
Weathering properties at sea of the F r ~ ycrude, the Lillefrigg condensate and
the 75:25 blend of these products
IKU Petroleumsforskninga.s
IKU Petroleum Research
N-7034 Trondheim, Norway
Telephone: +47 73 59 11 00
Attn.: Torleif Norenes
REG. NO.
DATE
PROJECT MANAGER
96.073
5 ~ u g u s t 1996
,
Per Johan Brandvik
NO. OF PAGES
NO. OF APPENDICES
LINE MANAGER
5
104
>s$~~d
SIGN.
SIGN.
Ivar Singsaas
& LS
SUMMARY
By combining results from laboratory investigations and IKU's Oil Weathering model, the weathering of
the Frgy crude oil over time under different weather conditions is predicted. These predictions are
presented in figures on standardised data sheets showing the different properties of the oil with
increasing weathering. This manual is intended to be a contingency planning tool for "On-scene
commanders" in ELF Petroleum Norge and for authorised oil spill personnel to facilitate decision
making concerning the use of different countermeasure techniques during an oil spill combat with the
Frgy crude.
The following main conclusions were found for the weathering of the Frgy crude:
Maximum water uptake is approximately 70 %.
The Frgy crude is chemically dispersible up to a viscosity of approximately 6000 CP.
Time window for use of dispersants is from 12 hours to several days depending on sea temperature
and sea state.
The following main conclusions were found for the weathering of the Lillefrigg condensate:
Maximum water uptake is approximately 70 %, but the emulsions formed were very unstable and
had a very high rate of natural dispersion.
Mechanical recovery or dispersants are not expected to be used on this product due to a high
tendency for natural dispersion and a high evaporative loss.
KEYWORDS ENGLISH
Oil spill
Oil weathering
Computer model
KEYWORDS NORWEGIAN
Oljesgl
Forvitring av olje
Modellering
PREFACE
As long as crude oils and petroleum products are transported across the seas by ships or pipelines there
will be the risk of spillage with the potential to cause significant environmental damage. The "Braer"
incident in Shetland and recent smaller ship accidents in Norway, have demonstrated the high level of
public concern about the damaging effects of oil spills. These spills also demonstrated the need for a
rapid decision-making process to assess the feasibility and effectiveness of difSerent countermeasure
techniques such as mechanical recovery, burning or dispersants.
New types of crudes are constantly being put into production from the Norwegian continental shelf: The
large variations in the physico-chemical properties of the crude oils make their behaviour vary widely at
a possible oil spill at sea.
Weathering (principally evaporation and emulsification) will change the physico-chemical properties of
the oils as a function of time, weather conditions and the original composition of the oil. Some of the
weathering processes will tend to accelerate the disappearance of the oil from the surface, while others
make the oil more persistent.
A good knowledge of the weathering properties of different oil types is fundamental for:
oil spill contingency planning for different oilfields.
optimisation of a mechanical, chemical or a burning combat operation with a specific oil type.
The changing properties of the oil or w/o-emulsion will grkatly influence the efficiency of a mechanical
combat operation:
containment operations depend on the spreading properties of the oil
leakage of oil from booms depends on the viscosity of the oil or w/o-emulsion.
pumping capacity of skimmer depends on the viscosity of the oil or w/o-emulsion
effectiveness of an w/o-emulsion breaker depends on the w/o-emulsion stability which depends on
the properties of the oil.
The efficiency of a chemical combat operation depends on factors such as:
the physicaUchemica1 properties of the oil (viscosity, war content, pour point etc.)
the spreading properties of the oil
the water content and w/o-emulsion formation properties
the viscosity of the w/o-emulsion
The aim of this manual is to be a tool in the contingency planning for the "On-Scene Commanders" in
ELF Petroleum Norge and other oil spill personnel. It will facilitate decision making on the most
appropriate use of different countermeasure techniques during oil spill combat operations to spills of
Fr@ycrude or the Lillefrigg condensate. The manual also contains information of a more general nature,
indicating the complexity of weathering of oil at sea.
The laboratory testing of the weathering properties of the Fr@ycrude and the Lillefrigg condensate was
carried out to a standardised laboratory procedure which has been developed at IKU. The experimental
laboratory data has been used as input to the IKU Weathering Model. By combining the experimental
data with the IKU Weathering Model, it is possible to predict the weathering properties of FrGy oil
during different weather conditions. These predictions are presented as data sheets showing the different
properties of the oil with increased weathering.
The assistance from laboratory and office staff at IKU Lars Hovdahl, Anita Johansen and Oddveig
Bakken (laboratory technicians), May Kristin Ditlevsen (secretary) and Tone Aas Heggenhougen
(illustrator), are gratefully acknowledged.
Trotzdheim, May 1996
Per Johatl Brandvik
Project manager
SIYTEF QROUP
TABLE OF CONTENTS
.
Page
1 A BRIEF INTRODUCTION TO COMPOSITION AND PROPERTIES OF CRUDE
OILS
7
1.1 Composition of crude oils ............................................................................................................ 7
1.1.1 Hydrocarbons ................................................................................................................ 7
1.1.2 Non-hydrocarbons ......................................................................................................... 7
1.2 Properties of crude oils ................................................................................................................ 8
1.2.1 Boiling point and boiling range (distillation properties)................................................ 8
1.2.2 Density ........................................................................................................................... 8
1.2.3 Viscosity ........................................................................................................................ 8
1.2.4 Pour point ...................................................................................................................... 9
1.2.5 Flash point ..................................................................................................................... 9
.
..................................................................................................................................................
.....................................................................
l1
2 THE BEHAVIOUR OF CRUDE OIL SPILT AT SEA
2.1 Evaporation................................................................................................................................ 12
2.1.1 Effect of evaporation on properties of remaining oil .................................................. 12
2.2 Water solubility (dissolution) of oil components ...................................................................... 13
2.3 Photo-oxidation .........................................................................................................................14
2.4 Biodegradation........................................................................................................................... 14
2.5 Sedimentation ............................................................................................................................ 14
2.6 Submerging................................................................................................................................14
2.7 Water-in-oil emulsification ........................................................................................................ 14
2.7.1 Formation of wlo-emulsions ........................................................................................ 14
2.7.2 Stability of wlo-emulsions ..........................................................................................16
2.7.3 Rheology (flow behaviour) of wlo-emulsions .............................................................. 17
2.7.4 Effect of water-in-oil emulsification on oil spill countermeasures ..............................17
2.8 Natural and chemical dispersion (oil-in water) ......................................................................17
2.9 Spreading ................................................................................................................................... 18
2.10 The drift of the oil spill ...........................................................................................................18
.
...........................................................................................................
3 EXPERIMENTAL METHODS
19
3.1 Oils tested ..................................................................................................................................
19
3.2 Preparation of weathered residues ............................................................................................19
20
3.3 Physico-chemical analyses .........................................................................................................
20
3.4 Emulsification studies ................................................................................................................
3.4.1 Preparation of wlo-emulsions ......................................................................................
20
3.4.2 Methods for testing of demulsifiers .............................................................................
21
21
3.5 Chemical dispersability studies ..................................................................................................
3.5.1 Methods used ...............................................................................................................21
21
3.5.2 Dispersants used ..........................................................................................................
3.6 Meso-scale flume studies ...........................................................................................................
22
3.6.1 Description of the flume ..............................................................................................23
3.6.2 Flume test methodology ...............................................................................................
23
...............................................................
4. WEATHERING PROPERTIES OF THE FR0Y CRUDE
25
4.1 Physico-chemical properties ......................................................................................................
25
4.1.1 Chemical composition .................................................................................................
25
26
4.2 Water-in-oil emulsification ........................................................................................................
4.2.1 Rate of formation .........................................................................................................
26
28
4.2.2 Viscosity ......................................................................................................................
4.2.3 Stability of wlo-emulsions and effectiveness of emulsion breaker ..............................28
4.3 Chemical dispersability testing ..................................................................................................
31
4.3.1 Initial screening of dispersants ....................................................................................
31
32
4.3.2 Comprehensive dispersability testing of the Fray crude ..............................................
SINTCC
4.3.3 Dispersability testing of the Lillefrigg condensate and blends of Fray crude
and Lillefrigg condensate .............................................................................................
33
34
4.4 The meso scale flume test ..........................................................................................................
4.4.1 Water uptake................................................................................................................
34
34
4.4.2 Viscosity of wlo-emulsion ...........................................................................................
4.4.3 Emulsion stability and effectiveness of emulsion breaker ...........................................34
4.4.4 Natural and chemical dispersability of the Fray crude ................................................34
4.4.5 Evaporative loss ..........................................................................................................34
4.4.6 Mass balance .............................................................................................................. 35
.
.......................................................................................
.
................................................................................................
5 PREDICTION OF PROPERTIES AT SEA
37
5.1 Introduction ............................................................................................................................... 37
5.1.1 Numerical weathering model ....................................................................................... 37
5.2 Criteria used for the predictions................................................................................................. 38
5.2.1 Discharge conditions and time-scale for predictions ................................................... 38
5.2.2 Oil film thickness........................................................................................................ 38
5.2.3 Wind and sea state conditions ..................................................................................... 38
5.2.4 Sea temperatures.......................................................................................................... 38
5.2.5 Fire and explosion hazard ............................................................................................ 38
5.2.6 Laboratory investigation............................................................................................. 38
5.2.7 Optimised mechanical recovery ................................................................................... 39
5.3 Prediction tables-user examples ................................................................................................. 39
41
5 PREDICTED PROPERTIES AT SEA
5.4 Fray crude. list of prediction tables (Blue pages): ..................................................................... 41
5.5 LilleFrigg condensate. list of prediction tables (Red pages): ..................................................... 41
5.6 Fray and LilleFrigg blend (75.25). list of prediction tables (Green pages): ..............................41
.
7.
6 SUMMARY OF THE WEATHERING PROPERTIES OF FRBY CRUDE AT SEA
SUMMARY OF THE WEATHERING PROPERTIES
CONDENSATE AT SEA
OF
...................69
LILLEFRIGG
..............................................................................................................71
.
8 SUMMARY OF THE WEATHERING PROPERTIES OF THE FRBY LILLEFRIGG
BLEND (7525) AT SEA
...............................................................................................................73
9. REFERENCES ......................................................................................................................................75
...............................................................................................77
APPENDIX B: Emulsification (water uptake and stability) and demulsification results ..................87
APPENDIX C: Chemical dispersability results .....................................................................................91
y
.............................95
APPENDIX D: Meso-scale flume results. (Only performed with the F r ~ crude)
APPENDIX A: Physico-chemical results
APPENDIX E: F r ~ y
crude. Lille-Frigg condensate and the 50:50 and 7525 blend
between them compared to other Norwegian sector crudes
...............................................................l01
QROUC
1.
A BRIEF INTRODUCTION TO COMPOSITION AND PROPERTIES
OF CRUDE OILS
A crude oil is not a uniform material. The chemical
composition and therefore chemical and physical
properties of different crudes vary over a very wide
range.
Hydrocarbons are divided into aliphates and
aromatics and the two main groups of aliphates are
paraffins and naphthenes.
Paraffins
1.1
Composition of crude oils
Crude oils are a complex mixture of thousands of
chemical components. The relative composition will,
however, vary greatly between different crudes,
resulting in variations in the physico-chemical
properties. Figure 1.1 shows schematically the
division of the crude oil into the main chemical
groups.
This includes n-alkanes (straight chain) and isoalkanes (branched chain) aliphatic compounds.
Waxes are an important sub-group of paraffins,
containing more than 20 carbon atoms. The wax
components of a crude oil will be present in solution
at elevated temperatures. At low temperatures they
may precipitate out of solution. These are principally
n-alkanes. The wax content of crude oils can vary
from 0.5 wt.% up to 40 or 50 wt.% in extreme cases,
although the majority of the world's crude oils have
wax contents of 2 - 15 wt.%.
Naphthenes
This group includes cycloalkanes containing one or
more saturated rings. Each ring may have one or
more paraffinic side chains. They are chiefly 5 and 6
membered rings.
I l,
A
Aromatics
Aromatics
These are a spesific group of unsaturated, cyclic
hydrocarbons. The presence of straight or branched
chain paraffinic side chains produces a large number
of isomers. Examples of low molecular weight
aromatic components include benzene, toluene,
xylenes.
Figure l .l
1.1.1
The chemical composition of the crude
oil. Division into chemical groups.
Hydrocarbons
The majority of compounds in crude oils are
hydrocarbons, composed of hydrogen (10-15 wt.%)
and carbon (85-90 wt.%). These range from simple,
volatile gases, such as methane with only one carbon
atom, up to large, complex molecules with more than
100 carbon atoms. The hydrocarbons in crude oils
include saturated and unsaturated molecules in
linear, branched and cyclic configurations.
IKJ 1061 1 M \\Boss\ikd 1961 1 OO\Fr~v\KAPPORT?m~ter~.~iocLune\7U15
08.96
In addition to pure hydrocarbons, some organic
compounds in crude oils also contain small amounts
of oxygen, nitrogen, or sulphur, and some trace
metals such as vanadium and nickel. The two most
important groups of non-hydrocarbons are resins and
asphaltenes.
Resins
Resins are relatively polar compared to the
hydrocarbons, and often have surface active
properties. Resins have molecular weights ranging
from 700-1000. Carboxylic acids (naphthenic acids),
sulphoxides and phenol-like compounds can be
found in this group.
Asphaltenes
This is a complex group of poorly characterised
chemical compounds. They consist of condensed
polycyclic aromatic compounds. They are large
molecules with 6 - 20 aromatic rings and side chains
(molecular weight: 1000 - 10 000). Asphaltenes may
be classified as "hard"' or "soft", on the basis of the
method used to determine the asphaltene content.
Crude oils can contain up to 6 wt.% "hard"' and 10
wt.% "soft" asphaltenes.
1.2
Properties of crude oils
The physical and chemical properties exhibited by a
crude oil are a result of the properties of its
constituent chemical components. Because the
chemical composition of different crude oils varies
over a wide range, the physico-chemical properties
also vary.
1.2.1
Boiling point and boiling
(distillation properties)
The distillation curve is an indicator of the relative
amounts of different chemical components,
principally as a function of molecular weight, but
also determined by the chemical composition. Figure
1.2 shows the distillation curves of 6 Norwegian
crude oils.
1.2.2
Density
The density of crude oils ranges from approximately
0.780 to 1.000 kg/L (49.9 - 10.0 "API) at 15°C. Low
density crudes are typically high in low molecular
weight paraffinic components, whilst crudes rich in
high molecular weight aromatic, naphthenic and
asphaltenic components will have higher densities.
In American literature the density of oil is often
given as API gravity and expressed as "API, where:
"API =
141.5
Specific gravity
- 13 1.5
range
The distillation curve indicates the relative
distribution of volatile and heavier components in
the oil. The distillation curve is obtained by
measuring the vapour temperature as a function of
amount of oil distilled.
Specific gravity of a crude oil is defined as the ratio
between the density of the crude at 15.5"C (60°F)
and the density of distilled water at the same
temperature.
1.2.3
Viscosity
The viscosity of a crude oil defines its resistance to
flow and is due to the viscosity of its constituent
components. Low molecular weight compounds
generally have lower viscosity than higher molecular
weight compounds.
The viscosity of crude oils world wide ranges from 3
- 2000 cP at 13°C. For most oils the viscosity is
0
100
200
300
400
500
600
Boiling point ("C)
Figure 1.2
Distillation curve (volume percent
evaporated versus temperature) of 6
Nonvegian crude oils.
given either at 15.5"C (60°F), 37.8"C (100°F) or at
50°C. Figure 1.3 shows the variation in viscosity as a
function of temperature for typically Norwegian
crude oils and oil products. Waxy or very viscous
crudes can exhibit non-Newtonian behaviour
(viscosity varies with shear rate), especially close to
or below their pour point.
1.2.5
IF-30
Gullfaks
Frey
EkofisWla
' 0
10
20
30
40
50
60
Temperature ('C)
Figure 1.3
1.2.4
Variation in viscosity as a function of
temperature for typically Norwegian
crude oils and oil products. The figure
may not be valid when the
temperature is near the pour point of
the oils.
Pour point
The pour point is the temperature at which an oil
ceases to flow when subjected to a slight movement,
when it is cooled without disturbance under specified
laboratory conditions. It is not possible to accurately
translate this into the temperature at which the oil
will become semi-solid in other circumstances. (e.g.
at the sea surface see 2.1.1). The pour point is
related to the chemical composition of the oil,
particularly the wax content. As a crude oil is
cooled, small wax crystals can precipitate.
Highly paraffinic crudes can have high pzur points
due to high wax contents, in excess of 30 C for the
more extreme paraffinic crudes. Naphthenic crude
oils, especially Ifw viscosity crudes, can have pour
points below -40 C. This is partly due to the absence
of waxy components and also to the ability of the
low molecular weight naphthenic components to
maintain the wax in solution.
Flash point
The flash point is the lowest temperature at which
the gas or vapour generated by heating an oil can be
ignited by a flame. The flash point depends on the
proportion of low molecular weight component.
Fresh crude oils have a low flash point (from -40 to
+30°C) because of the high proportion of low
molecular weight components.
From the viewpoint of safety, flash points are of
most significance at or slightly above the maximum
temperature that may be encountered in storage or
transport. The flash point is an approximate indicator
of the relative fire and explosion hazard of an oil.
The oil's flash point will rise rapidly after the oil
being discharged at sea because of the evaporation
of the lightest components. Criteria for fire and
explosion hazard connected to oil spills and oil spill
combat at sea are given in section 5.2.5 (EPA,
1982).
A rule of thumb says that staying in an oil spill
where the flash point of the oil is close to or lower
than the sea temperature implies fire and explosion
hazard. Practically, this means a relatively short
period of danger (less than 1-3 hours, depending on
the weather conditions and discharge criteria) after
discharge of a crude oil. It is important, however, to
emphasise that the oils' flash point only is one of
several parameters infl~encingthe flammability of
the air over an oily surface. In the laboratory, the
flash point is measured in a closed system where
there is equilibrium between components in oil and
gas. In the field, however, the weath-er situation will
have great influence on the flammability of the air
above the slick. For instance the gas concentration
will be high just above the oil in calm weather and
high temperature, whereas it will be rather low in
cold and windy weather due to dilution and transport
and a lower degree of evaporation. Therefore the
criteria given in section 5.2.5 is very conservative
from an operational point of view.
Ka!l
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2.
THE BEHAVIOUR OF CRUDE OIL SPILT AT SEA
When oil is spilt at sea, a number of weathering
processes produce changes in the physical and
chemical properties of the crude and in the oil's
behaviour at sea. The main factors influencing the
oil's degree of weathering at sea are:
Original physical and chemical properties.
Environmental conditions (waves, wind,
sunlight. temperature).
Figure 2.1
Propertie:; of the water (current, temperature,
salinity, density oxygen, bacteria, nutrients,
presence of particles etc.).
Figures 2.1 and 2.2 show schematically the different
processes and how their relative importance varies
with time.
Weathering processes of oil or1 water.
Figure 2.2 (next page) illustrates the different
weathering processes relative importance affecting
the oil slick at sea.
For example is evaporation most important the first
days after the spill, while biodegradation is not a
significant proc,ess (regarding oil spill contingency)
before 1 to 2 weeks after the spill.
(0-
Hours
1
-
p
-
1
0
1
Day
'
0
0
Week
1000
Month
- - Y e a r10000
Evaporation
Dissolution
Photo-oxidation
Biodegradation
Sedimentation
Water-in-oil
emulsification
emulsion
Oil-in-water
dispersion
Stable 'mousse'
l
Spreading
I
Drifting
Figure 2.2
2.1
Weathering processes' relati\'e importance with titne.
Evaporation
As the oil spreads over the water, evaporation of the
lightest components will occur. This is one of the
most important weathering processes which removes
oil from the water surface.
The rate of evaporation will, in addition to the
relative containment of lighter components in the
crude, also be a function of wind speed, sea
temperature and thickness of the oil film. The rate of
evaporation will therefore vary from spill to spill.
A commonly used generalisation is that all
components with boiling points lower than 200°C
(up to n-C1 1 ) will evaporate within 12 - 24 hours.
while components with boiling points up to 270°C
(less than n-C15) will disappear from the spill within
several days. A large proportion of the volume of
light crude oils will therefore evaporate rapidly. The
proportion of heavier crudes that remains on the sea
surface will be greater. Light refinery products like
gasoline (boiling point range 30 - 180°C) and
kerosene (130 - 250°C) u,ill totally evaporate after
some hourslfew days at the water surface. Figure 2 . 3
shows the predicted evaporative loss for six North
Sea crude oils, as a function of weathering at sea
calculated under given weather conditions.
2.1.1
Effect of evaporation on properties
of remaining oil
An important consequence of the evaporation
process is that the remaining oil at the surface has
change physico-chemical characteristics compared to
those of the original oil:
Density
The density of the oil is important for the spreading
of the oil and for the degree of naturallchemical
dispersion. Figure E6 in Appendix E shows the
predicted density of oil-in-water emulsion as a
function of weathering at sea for different crude oils
under glven weather conditions.
Viscosity
The viscosity of the oil will increase, due to loss of
the l i ~ h t e r , less viscous components and a
consequently larger proportion of heavier, more
viscous components in the remaining oil residue. For
mo\t of the North sea crudes the increase in vihcosity
Lvill t p i c a l l y be in the range from 5 to 2 0 c P for the
fresh crude to few hundred c P for the residue.
5
10
15
20
Weathering time at sea (hours)
Figure 2.3
Degree of evaporation as a function of time at sea. Calculated for 5 m/s wind, 15°C sea
temperature andfilm thickness decreasing from 20 mm to 2 mm with a half-time of 1 hour.
Pour point
The pour point of the remaining oil will also be
higher than that of the original oil because the !oss of
the more volatile components will concentrate the
wax in the remainder, leading to wax precipitation
and a higher pour point. However, at the sea surface
the oil may remain a liquid, and spread over the sea,
at temperatures as low as 10 - 15 "C lower than the
pour point of the oil (see also 4.1.2, pour point).
In Figure E3 in Appendix E, the pour point is
predicted for different crude oils under given
weather conditions, and plotted as a function of time
at sea.
Flash point
The flash point of the oil remaining on the surface
will rapidly increase as the more volatile and
inflammable components evaporate and are rapidly
diluted into the air.
As the volatile components evaporate and the flash
point of the residue increases, the risk of fire and
explosion will rapidly decrease. Higher wind speeds
cause faster evaporation and diffusion of the vapour
and therefore a more rapid increase in flash point.
In Figure E2 in Appendix E the flash point is
predicted for different crude oils under given
weather conditions, and plotted as a function of time
at sea.
2.2
Water soIubility (dissolution) of
components
oil
The heavier hydrocarbon compounds in crude oils
are essentially insoluble in water, while the smaller
molecules (especially aromatics, such as benzene
and toluene) dissolve to some extent. However, these
compounds are volatile and also evaporate rapidly.
Typically, the evaporation is 10 - 100 times quicker
than the solubility into the water phase.
The concentration of oil components dissolved in
water under an oil spill will therefore be very low
(less than 1 mg/L) and water solubility has only a
very minor effect on the total removal of oil from the
sea surface. If there is a high
degree
of natural
dispersion, dissolution will become more important.
2.5
Sedimentation
Under the influence of sunlight some of the oil
components (especially aromatics) will slowly be
oxidised to resins and eventually asphalthenes. This
contributes to the stability of wlo-emulsions and
therefore has a large influence on the oils persistence
on the surface. The photo-oxidised components will
stabilise the wlo-emulsions. After a long period of
weathering at sea, tar-balls can be formed. Tar-balls
are broken down very slowly both at sea and on
beaches.
Very few crude oils will have a density higher than
sea water (1.024 kgL) even after extensive
weathering or emulsification. Weathered crude oil
residues will therefore not normally sink. In areas
with high concentrations of sediment these may
adhere to the oil and make it sink. Due to changes in
oil processing, heavy fuel oil is becoming more
dense and sinking and sedimentation may become an
increasing problem in future spills with heavy bunker
fuel oils.
2.4
2.6
Biodegradation
Submerging
Sea water contains many kinds of micro-organisms
(e.g. bacteria), some of which may use oil
components as an energy source. Even if the
concentration of micro-organisms at an accidental oil
spill at open sea is initially low, a rapid increase will
happen if the conditions are favourable. Important
factors influencing the rate of biodegradation are the
concentration of nutrients (nitrogen and phosphate),
oxygen and the temperature.
It has been observed that highly weathered and dense
oils can temporarily disappear from the surface, and
later return to the surface. Recent research has shown
that the degree of sub-merging of the oil is mainly a
function of sea conditions and the density and
viscosity of the oil or wlo-emulsion.
The most easily broken down components are the
straight chain saturated hydrocarbons (n-alkanes).
Several kinds of organisms exist, each preferring
their particular group of hydrocarbons. Principally,
all types of oil components, except asphaltenes, can
be broken down by microbial organisms.
Water-in-oil emulsification is the most important
weathering process that makes crude oils persistent
on the water surface. The formation of wloemulsions may delay the evaporation and the natural
dispersion processes by significantly increasing the
viscosity.
As these micro-organisms live in sea water, the
biodegradation will only take place at the interface
between oil and water. Oil that has stranded above
the tide-zone will be degraded extremely slowly and
may remain for many years.
In the sea, the formation of oil droplets by natural or
chemical dispersion will increase the biodegradation
rate at least 10 - 100 times compared to surface oil,
due to the increase in oiUwater interfacial area. Many
factors influence the biodegradation, and even after
many years of research it is very difficult to predict
the rate of the microbial biodegradation of an oil
spill. A rate of biodegradation of around 1-30 mg oil
3
pr m sea water per day has been reported. The rate
in more chronically oil polluted areas might rise up
to 0.5-6.0 g oil/m3 sea water per day. Oil trapped in
the sediments will remain for much longer because
the rate of biodegradation is much lower due to the
lack of oxygen and nutritients.
2.7
2.7.1
Water-in-oil emulsification
Formation of wlo-emulsions
Almost all crude oils contain surface active
compounds which cause them to form wlo-emulsions
if the energy at the sea surface is sufficient. The
presence of breaking waves (wind speed at more
than 5 d s ) has been set as the lowest energy limit
for water-in-oil emulsification, but a slower rate of
water uptake can also happen in calmer conditions.
Water-in-oil emulsification and natural (oil-in-water)
dispersion (Section 2.8) will proceed simultaneously
in the initial stages of a spill. As the oil viscosity
increases
due
to
weathering,
water-in-oil
emulsification usually becomes the dominant
process. However, in extreme conditions of high
wind speed, dispersion may be the dominating
process compared to emulsification (e.g. Gullfaks
crude in the Braer accident).
Sture Blend
o Oseberg feltsenter
X
Parent oil viscosity (cP)
Figure 2.4
Correlation between the viscosity of crude oil residues/emulsions and water content.
The rate of water-in-oil emulsification can vary
greatly among different crudes. Figure 2.4 shows the
correlation between the viscosity of crude oils and
their ability to take up water and form water-in-oil
emulsions.
Direct incorporation of water droplets by
wave-like instabilities at the oiltwater
interface.
Tests performed at IKU indicate that the maximum
water volume incorporated into emulsions of
different oils will be relatively independent of the
weather conditions, provided that the lower energy
barrier for water uptake is exceeded. Figure 2.5
illustrates how different wind speeds influence the
rate of water-in-oil emulsification for a typical crude.
Tests have shown that the chemical composition of
crude oils greatly influences the water-in-oil
emulsification rate. Wax rich crudes usually pick up
water more rapidly than lower wax content oils. As
the pour point of an oil is closely related to its wax
content, an oil near or below its pour point is likely
to produce w/o-emulsions quite rapidly.
The mechanism of water-in-oil emulsification is not
yet fully understood. Possible mechanisms include:
Re-surfacing of unstable oil droplets, formed
by natural dispersion, which may trap small
water droplets in the oil slick.
Breaking waves may form water filled
"bubbles" of oil which will also re-combine
with the slick.
Time (hours)
Figure 2.5
Example of the influence of rvirld
speed on the rate of rvater-irz-oil
emulsification.
Figure 2.6
Water droplet size in a w/o-emulsion after I hour ( A ) and 24 hours ( B ) mixing.
2.7.2
Not all of the water droplets incorporated into the oil
will be stable. The largest water droplets will sink
through the oil film and will settle out of the wloemulsion. Larger water droplets may be reduced in
size by the flexing, stretching and compressing
motion of a slick due to wave action. The wloemulsion will eventually contain only small water
droplets (1 - 10 pm diameter). Figure 2.6 illustrates
the influence of mixing time on water droplet size in
a wlo-emulsion.
Stability of wlo-emulsions
Resins, waxes and asphaltenes are very important
components which influence the stability of wloemulsions, because they form an interfacial film
between the oil and the water droplets (Figure 2.7).
This interfacial film is a physical barrier which
prevents coalescence to larger and more unstable
water droplets in the oil.
WATER PHASE
kphaltene
stabilized
Water droplet
- pm in diameter
& wax
OIL PHASE
ss j--iig/j
fJ
) stabilized
OPrs
ss
l3
-
Asphaltene "particles"
a Wax crystals
/' Resins
Figure 2.7
Interfacial film stabilization of w/o-emulsions.
))
F0
7o
@
2.7.3
Rheology (flow
emulsions
behaviour)
of
wlo-
Wlo-emulsions are more viscous than the parent oil.
Figure 2.8 shows an example of how the viscosity
ratio increases drastically with increasing water
content (Mackay et al., 1980). Wlo-emulsions
exhibit shear-thinning behaviour. An emulsion may
be quite liquid under turbulent conditions at sea, but
can become much more viscous, or even semi-solid
in calmer water conditions, or on beaches.
Measurements of the viscosity of wlo-emulsions
have therefore to be carried out under strictly
controlled conditions (defined shear rates and
thermal and mechanical history of the sample). At
IKU a shear rate of 10 S-' is routinely used for
expressing viscosity data on wlo-emulsions.
wlo-emulsion is less than 1000 cP because low
viscosity oils and emulsions may escape under the
boom. If the viscosity is higher than 10 000 cP, some
types of skimmers ( e.g. disc and mop skimmers)
have reduced recovery efficiency (see also chapter
5.2.7).
2.8
Natural and chemical dispersion (oilin water)
If sufficient energy is available on the sea surface,
waves will start breaking up the oil into droplets with
sizes ranging from 1 - 1000 pm in diameter. These
will be mixed into the water column. This happens
mainly when breaking waves are present (typically at
wind speed higher than 5 mls). The largest droplets
will resurface and form sheen behind the spill, as
described in Section 2.9.
Oil droplets less than 100 pm in diameter will have
rise velocities of less than 1 - 2 meter per hour. The
vertical and horizontal motion of these droplets will
be dominated by turbulence in the water column and
they may therefore be considered to be permanently
dispersed.
Water content (vol. %)
Figure 2.8
2.7.4
Example of the viscosity ratio as a
function of increasing water content
(Mackay et al., 1980)
Effect of water-in-oil emulsification o n
oil spill countermeasures
The properties of a wlo-emulsion (such as water
content, viscosity and stability) are of great
importance to the effectiveness of mechanical and
chemical oil spill countermeasures.
If mechanical recovery methods are to be used, the
water content of the emulsion will be important.
Water-in-oil emulsification vastly increases the
volume of pollutant to be recovered. An emulsion
containing 80 vol.% of water will have a volume of
five times that of the original oil. Experience from
Norwegian field trials (Nordvik et al., 1992) has
shown that the effectiveness of many mechanical
recovery methods is decreased if the viscosity of the
The rate of natural dispersion, in moderate weather
conditions, will be about 0.5 - 2 vol.% oil per hour in
the initial stages of a spill. Natural dispersion is one
of the most important processes that determines the
lifetime of the oil at the sea surface. Gradually, this
natural dispersion rate will decrease (see Figure 2.2)
as evaporation and water-in-oil emulsification
increases the viscosity of the oil or emulsion.
Chemical dispersants enhance the natural dispersion
rate by reducing the interfacial tension between the
oil and water. Field trials have shown that chemical
dispersion results in an increased oil concentration in
the water column down to approximately 10 meters,
shortly
after
dispersant
application.
This
concentration rapidly drops due to dilution caused by
vertical and horizontal mixing, and will be far below
the general toxicity level for most organisms in the
sea.
The increase in pour point caused by evaporation
can cause the oil to be very difficult to disperse.
Laboratory investigations have shown that oils are
chemically dispersable at 10 - 15°C below their pour
point. If the pour point of the oil or emulsion
exceeds the sea temperature by more than this, the
oil may not be chemically dispersable.
2.9
Spreading
Oil spilt at sea will spread on the sea surface. The
spreading can be very fast and is frequently the
dominant process in the initial stages of a spill,
although its importance decreases with time.
Tlck 011and
water-~n-011
emulslon (mm)
High density and viscosity of the oil will decrease
the spreading. If the pour point becomes higher than
the ambient sea water temperature, the spreading will
decrease rapidly as the oil becomes semi-solid.
Sheen (< lum)
After the initial stage, the oceanographic conditions
(current, waves and wind) will be the dominating
effect on the spreading of oil. The oil slick will,
because of the wind and waves, be broken into
"windrows", which will align with the direction of
the wind (Figure 2.9). he oil slick will spread
mainly in the downwind direction, with large
variations in the film thickness (by a factor of several
thousands).
A typical guide is that about 90% of oil will be as
patches
thick), covering
approximately 10% of the spill area. The remaining
10% of the
area
cover about 90% of the
in the form of "sheen" (< 1 Km thick). The average
spill thickness will be about 0.1 mm.
I
Figure 2.10
Wind - 20 knots
wlndmws
"'s,,-A..-mnp.
Figure 2.9
2.10
The spreading of oil and distribution
within the oil spill
The drift of the oil spill
Simultaneous with the above weathering processes,
the oil spill will be transported on the surface under
the influence of wind a i d current. Wind and waves
create a current in the water mass which, at the
is about 3% of the wind 'peed. In the
absence of wind, the oil spill drift is governed by the
prevailing current. Figure 2.10 illustrates how the
movement of the oil is influenced by wind and
current.
- - - - -
l
At1 example of horv the movement of the oil is influenced bp wind and currenl
l:lm
smunr a m o u r
3.
EXPERIMENTAL METHODS
All of the different weathering processes are
influenced by several factors such as temperature,
weather conditions and the properties and
composition of the oil.
To be able to predict how a particular type of oil will
weather at sea under different conditions, it is
necessary to know how the processes influence each
other. Knowledge of the different weathering
properties of the oil is therefore very important, both
to be able to optimise an oil spill combat operation
and in connection with contingency planning.
Numerical models for calculating the weathering
properties of oils at sea at different weather
conditions have been developed. These models often
combine theoretical and empirical considerations,
and can be very useful tools in a real oil spill
situation. However, the quality of the results from
these models is very dependent on the quality of the
available data put into the model. Good experimental
weathering data for the actual oil type improves the
accuracy of the predictions. This kind of exact data
is so far, however, only available for a number of the
Norwegian crude oils (the F r ~ ycrude and the
Lillefrigg condensate among approx. 25-30 other).
Laboratory data are therfore provided in this project
as input to IKUs Weathering Model to predict the
weathering properties of the F r ~ ycrude and the
Lillefrigg condensate at sea.
3.1
Oils tested
A sample of stabilised crude oil marked " F r ~ y
25/20" was delivered at IKU in January 1995 (IKU
nr: H3 107). The sample of the Lillefrigg condensate
was received in august 1995 (IKU nr: H3247). The
samples were supplied by ELF Petroleum Norge afs.
Two different blends were made from these product,
a 5 0 5 0 (IKU nr: H3292) and a 75:25 (IKU nr:
H3293) blend of Fr0y crude and Lillefrigg
condensate.
A full weathering study has been performed with the
Fr0y crude while the Lillefrigg condensate and the
two blends have been exposed to a full investigation.
3.2
Preparation of weathered residues
T o isolate the influence of the different weathering
processes (i.e. evaporative loss, photolysis and
water-in-oil emulsification), the weathering of the
oils were carried out using a systematic, step-wise
procedure established first at IKU in 1987 and later
on further developed (Daling et al., 1990). This is
illustrated in Figure 3.1.
The first step involved three different degrees of
evaporative loss by a modified ASTM D86182
distillation (Stiver and Mackay, 1984): the oils were
topped to 150°, 200' and 250°C+ vapour
temperature. This will approximately simulate the
evaporative loss that occurs at sea after 0.5-1 hour,
0.5-1 day and 2-5 days, respectively. Samples of the
fresh crude were also placed on sea-water, allowed
to spread into a thin film and photo-oxidised by
artificial sunlight for 20 hours. This caused an
evaporative loss corresponding to that of the 250°C+
residues.
Each of the topped and photolysed oil residues were
used to produce w/o-emulsions with three different
water contents; 50 vol.% water, (WOR, volumetric
water-to-oil ratio=l), 75 vol.% water (WOR=3) and
maximum vol.% water (WOR=max) (see Section
3.4).
Thus, 16 weathered oil residues and emulsions
were prepared from the F r ~ ycrude oil. Every
sample prepared in this way was subjected to
physico-chemical
analyses,
water-in-oil
emulsification studies (including the effectiveness
of demulsifiers) and chemical dispersability
testing. The fresh crude oils were tested for
physico-chemical
properties
and
chemical
dispersability only.
Only the 200°C+ residue and the corresponding 50
and 75% emulsions were prepared from the
Lillefrigg condensate and the two blends.
Evaporation
Crude oil
Figure 3.1
3.3
150%
20OoCt
250°C+
+
Ph.ox
Flow chart for weathering of a crude oil.
Physico-chemical analyses
The physico-chemical properties of the fresh, topped
and photo oxidised oil residues were characterised
by the analytical methods listed below:
The fellowing analysis were performed both on the
Fray crude. the Lillefrigg condensate and the blends.
Density: ASTM-method D4052-8 1.
Viscosity (dynamic): Haake Rotovisco RV20 or
Bohlin Visco 88 BV.
Pour point: ASTM-method D97-66
(IP-method 15/67).
Wax content: Precipitation of deasphalted oil in
2-butanone/dichlorometane (1+1, voI.+vol.) at 10°C. (Bridit et al., 1980).
"Hard" asphaltene content: IP-method 143184.
The following analysis were only performed on the
Fray crude.
Interfacial tension: ASTM-method 97 1-82 (de
Nouy ring method).
Saturate, aromatic and resin content: Iatroscan
TLCFID.
Flash point: ASTM-method D93-80
(IP-34/85).
The viscosity was measured on the oil residues and
the w/o-emulsions at shear rate 100 and 10 s-l
respectively.
3.4
Emulsification studies
Definitions
and
symbols
concerning
the
emulsification studies are given in Appendix B. The
procedures are described in detail by Hokstad et al.,
1993.
Only the 200°C+ residue and the 50 and 75%
emulsions were prepared from the Lillefrigg
condensate and the two blends.
3.4.1
Preparation of w/o-emulsions
The emulsifying properties of the four oil residues
were tested by using a standard laboratory method
(see Figure 3.2), which is a modified version of the
rotating flask procedure developed by Mackay and
Zagorski, 1982. The method uses cylindrical
separating funnels (0.5 L) with oil and sea water
rotated at 30 rpm for 24 hours and is simple and
rapid. Emulsions were produced at 13'C with
normal salinity (3.5%) sea-water.
A comparison of the emulsification rate of Ekofisk
and Oseberg crude oils, measured in both
experimental field trials and in laboratory studies
showed that the rotating flasks formed w/oemulsion six times quicker than with 10 m/s wind
speed in the field.
The following parameters were measured when
preparing the maximum water content emulsions:
Relative water-in-oil emulsification rate
(kinetics, represented by the tin-value).
Maximum water-in-oil emulsification ability
(WOR max., volumetric water-to-oil ratio).
3.4.2
Methods for testing of demulsifiers
'The demulsifier was added to an existing wloemulsion, and its ability to break the emulsion was
measured. The appropriate quantity (500 and 2000
ppm to oil) of demulsifier was added dropwise to the
emulsion. After a soaking time of 5 minutes and a
mixing time of another 5 minutes to mix the
emulsion breaker into the emulsion, the treated
emulsion was allowed to settle for 24 hours. The
amount of water that settled out after 24 hours was
recorded. These results were compared with those
obtained in the absence of demulsifier.
Before mlxing
24 hours
mixing
24 hours mixing
24 hours settling
Methods used
There is no single laboratory method for testing the
effectiveness of dispersants that is generally
accepted as being a good simulation of all
conditions at sea. Many different test methods have
been devised. The results obtained from these
methods vary due to different energy input. As no
single method can adequately simulate the range of
conditions at which the dispersion process can
occur at sea, it is important to use at least two
methods to assess the dispersability of oil residues
and emulsions. The tests used in this study were:
(Institute Francais du Pttrole test, Bocard et
al., 1984), is the official method for French
approval of dispersants. It is a low energy input
test (compared to the MNS-test described
below). It is probably a more realistic approach
than some other test methods because of the use
of continuous dilution. The sampling is dynamic
(taking place continuously during the mixing
period).
m,(Mackay and Szeto, 1980) has been the
approval method for Canada. The energy input in
this system, applied by blowing air across the
oillwater surface, producing a circular wave
motion, has been estimated to correspond to a
medium to high sea-state condition. The sample
of the oily water is taken under dynamic
conditions.
011
(30 ml)
Seawater
(330 ml)
Figure 3.2
Principle of the rotating flask
method (Mackay and Zagorski,
1982).
3.5
3.5.1
Chemical dispersability studies
The purpose of testing the chemical dispersability
of the oil residues and wlo-emulsions was to define
how the effectiveness of different dispersants
decreases as the oil weathers. This information is
required to effectively model and predict the timewindow for use of dispersants on various crudes at
different weather conditions (Daling et al. 1990).
Only the Fray crude was exposed to the total
dispersability testing, as described below. The
Lillefrigg condensate and the blends were only
tested with the IFP test.
The two laboratory methods are schematically shown
in Figure 3.3. The standard test conditions of 13°C
and 3.5% salinity sea-water were used. The results
from these test methods are mean values of three
replicates. The general standard deviation for the
IFP-test method is 4-6%.
As the oil viscosity increases due to weathering,
water-in-oil emulsification usually becomes the
dominant process. However, at high wind speeds
some oils may disperse instead of emulsify (e.g.
Gullfaks crude in the Braer accident)
3.5.2
Dispersants used
The screening testing was only performed on the
Fray crude.
At the initial stage of dispersability testing, eight
different dispersants were tested with the IFP
method, using the 200"C+ waterfree residues and
their 50 vol.% emulsions .
A. IFP Test
1. Experimental beaker
6. Electro-magnet
B. Oil containment ring
B. MNS Test
I
Orifice flow meter
I
Air outlet
Water sampling tube
1
l
Oil containment ring
Figure 3.3
Laboratory apparatus for effectiveness testing of dispersants.
Table 3.1
Dispersants included in the
screening tests of the Fr@ycrude.
Dispersants
Approved
in Norway
Corexit-9500
Dasic-NS
Dasic LTS
Dispolene 36s
Enersperse 1037
IKU-9
Inipol IPC
OSR-5
Yes
Yes
Yes
Yes
Yes
NO
No
Yes
Different criteria were used in the selection of these
products:
Seven of these dispersants (not IKU-9) are
commercially available, and six of the products
are approved for use in Norway.
Some of them have shown relatively high
effectiveness in earlier investigations at IKU.
Based on the results from the screening programme,
only two of the dispersants, Corexit 9500 and Dasic
NS, were used in further effectiveness testing using
the IFP and MNS test methods.
The chemical dispersability of the fresh oil, the four
waterfree residues and residues emulsified with 5 0
vol.% water (WOR=l), 75 vol.% water (WOR =3)
and maximum vol% (WOR=max) were tested. The
dosage ratio (DER, dispersant w/o-emulsion
volumetric ratio) was 1 :25.
3.6
Meso-scale flume studies
When studying the weathering effects on different
oils, it is important that the crudes are exposed to as
realistic conditions as possible. In the step-wise
small scale laboratory procedure, the oils are
mmmr a m o u r
evaporated (topped), photo-oxidised and emulsified
in separate processes independently of each other.
In an oil spill situation at sea, these processes will
take place simultaneously and will influence each
other.
To study these weathering processes simultaneously,
as in the field, but under controlled conditions, a
meso-scale flume basin has recently been built at
IKU (Singsaas et al., 1993). The flume acts as a link
between the step-wise small scale weathering in the
laboratory and field trials. This flume basin is an
important supplement to the existing laboratory
procedures to give experimental data input to
numerical models used for predicting oils' behaviour
at sea. Only the F r ~ ycrude was tested in the flume
basin.
3.6.1
The evaporative loss was estimated by comparing
the measured density of the waterfree surface oil
from the flume with densities predicted using the
IKU Oil Weathering Model assuming zero water
uptake in the oil. In this situation the densitychange of the crude will only depend on
evaporation. The estimated evaporative loss of some
of the surface oil samples were also compared by
examination of the GC chromatograms of the same
samples.
Description of the flume
The 10 m long meso-scale basin (Figure 3.4),
where approximately 1.7 m3 sea-water is circulated,
is placed in a temperature controlled climate room (
-20°C to 50°C). Energy for the formation of wloemulsions and dispersion is supplied by a wave
generator, and the degree of breaking waves can be
altered. Various wind velocities can be produced by
two fans placed in a wind tunnel. A sun-lamp is
available to provide photo-oxidation. The test
temperature was 13°C and the salinity of the sea
water 3.5 wt.%.
3.6.2
Density.
Emulsion stability. (Dehydration during settling,
D)
Effectiveness of emulsion breaker.
Chemical dispersability.
(Chemical dispersability using Dasic NS with
the IFP test method.)
Evaporative loss.
Flume test methodology
The meso-scale testing was only performed with the
F r ~ ycrude. 9 litres of fresh, stabilised F r ~ ycrude
were carefully released on the water surface,
producing an average oil film thickness of
approximately 2 mm. The water flow is created by a
wave generator. The fans caused the oil to move
around the full circuit of the flume in about 2
minutes.
The oil was weathered for 72 hours. Sampling of
surface oil residue and wlo-emulsion (containing
different amounts of water) and subsurface water
(containing different amounts of oil) was performed
at the following time intervals after oil release: 0
min, 15 min, 30 min, 1 hour, 2 hours, 4 hours, 8
hours, 12 hours, 1 day, 2 days and 3 days.
The surface wlo-emulsions were subjected to the
following analyses:
Water content.
Viscosity.
Monitoring of the dispersed oil was performed using
an in-situ UV fluorescence detector. Subsurface
water samples were analysed by extracting the 1 L
samples with DCM (dichloromethane). The amount
of oil was quantified by using a W adsorption
spectrophotometer. These resultss were used to
calibrate the in-situ UV fluorescence detector.
1. Wave generator
2. Photolysis (sun-lamp)
3. Wind-tunnel
4. Sub-surface sampling
Boss\ik41961100hegnertfig-enp/mesoflu~e.eps
Figure 3.4
Schematic drawing of the meso-scaleflume (seenfrom above)
4.
WEATHERING PROPERTIES OF THE F R 0 Y CRUDE
The results of the full weathering study of the Fray
crude are compared with the results from five other
Norwegian crudes in this chapter. These crudes are:
Heidrun, Statfiord, Gullfaks, Veslefrikk and Sture
Blend.
The results of a reduced study of the Lillefrigg
condensate and the 75:25 and 5050 blends of Fray
crude and Lillefrigg are mainly compared with the
results from the pure Fray crude, and these figures
are given i Appendix A.
4.1
Oil type
nC,/pristane and nC,Jphytane
Ratios of crudes tested by gas
chromatographic analysis.
nCI7/pristane
Fray
Heidrun
Sture blend
Statfjord
Gullfaks
Veslefrikk
nCl$phytane
1.1
1.2
1.8
1.5
0.1
1.4
2.7
1.5
2.4
1.9
0.1
1.6
Physico-chemical properties
The physical and chemical properties of the different
residues (degrees of weathering) for the Fray crude,
the Lillefrigg condensate and the blend are shown in
Figure A1 - A9 and listed in Table A1 - A2 in
Appendix A.
In this chapter the physico-chemical properties of
Fray and Lillefrigg are discussed. The corresponding
properties of the 75:25 blend of these two products
are rather similar to the properties of the pure Fray
crude.
4.1.1
Table 4.1
Chemical composition
The chemical composition of the Fray crude and the
topped residues (150°C, 200°C and 250"C+),
characterised by gas chromatography (GC), is shown
in Figure A8. In the figure it can be seen that the
photo-oxidised residue has a very similar GC
chromatogram to the 250°C+ residue.
The GC-chromatograms in figure A9 reveal an oil
component composition which is very similar to
other parafinic North Sea crudes e.g. Veslefrikk and
Statfiord.
Gas chromatography is an important tool in
identifying the source of an oil spill. One of the
screening identification parameter
is
the
nCI7/pristane and nC18/phytane ratio. Expanded
sections of the chromatograms are shown in Figures
A8 and A9 for the fresh crudes. Table 4.1 lists the
ratios, calculated of the peak areas of the crudes
shown in figure A9.
The combination of a relatively low nCI7/pristane
and a high nC,$phytane ratios as observed with the
Fray crude is very unusual compared to other
paraffinic crudes e.g. Veslefrikk and Statfjord. These
unique marker component ratios will facilitate the
identification of the source in case of an oil spill with
the Fray crude.
Liquid chromatography analysis reveals a low
content of resins in the Fray crude. The content of
saturated components is relatively high. Photooxidation caused an increase in the resin content.
This was expected because aromatic compounds are
oxidised into more polar compounds during photooxidation (see section 2.3).
Evaporative loss (Distillation)
The volume of the Fray crude oil distilled at 150°C,
200°C and 250°C is listed in Table A2 in Appendix
A.
Fray crude contains a relatively high proportion of
volatile components, and the extent of evaporative
loss will therefore be relative high.
The Lillefrigg condensate is a rather heavy
condensate, compared to other North Sea
condensates. After 6 hour at sea is almost 90 % of
the two North Sea condensates Sleipned and
Midgard evaporated, while only 35% from the
Lillefrigg condensate.
The volume lost at these distillation temperatures is
related to the oil volume that would be lost by an oil
slick at sea. The composition of the 150°C+ residue
is similar to that of oil spilt on the sea surface after
30 minutes to 1 hour weather exposure, the 200°C+
residue is representative of oil exposed for 12 to 24
hours, and the 250°C+ residue resembles oil that has
been on the surface for 2 to 5 days. These results
indicate that, after several days at sea, the Fray crude
will have lost up to 40% of its volume.
Density
The density of the fresh Fray crude (0.836 kglrnl) is
amongst the lowest of the Norwegian crudes, but the
density of both the fresh and weathered oil residues
are similar to other paraffinic crudes like e.g
Veslefrikk and Statfjord (see Figure A2).
time. A pour point of 10-15°C higher than the sea
temperature is considered to be reducing the effect of
dispersants. The spreading rate of the oil will
decrease as the pour point increases.
The pourpoint of the Lillefrigg condensate is also
high due to the high vax content. The pour point is
10°C for the fresh condensate and 19°C for the
200°C+ residue.
Wax
The density of the Lillefrigg condensate is rather
high compared to other North Sea condensate (0.785
kgtl) due to its high amount of heavy components.
Viscosity
The viscosity of the water free oils and residues has
an influence on the effectiveness of transfer
operations, e.g. pumping of mechanically recovered
oil after settling of water from the emulsion. Fresh
Fray crude oil has a viscosity of 10 cP at 13°C. As
the oil loses the more volatile components by
evaporation, the viscosity of the remaining residue
increases. The Fray crude has generally a high pour
point and viscosity measurements is difficult when
the waterfree residues becomes semi solid (250°C+
residue). The viscosity for both the fresh and the
weathered residues is similar to other Norwegian
oils, except from the 250°C+ residue were probably
a too high viscosity was measured due to pour point
problems.
Fray crude has a very high wax content (5.1 wt% for
the fresh crude) compared to most other North sea
crudes (see Figures A5). There is a relatively good
correlation between the wax content of the crude and
the pour point results. High wax contents give high
pour points. The wax content of the crude also
correlates with the rate of water-in-oil emulsification
(see Section 4.2). Crudes with a high wax content
have usually rapid water uptakes.
The vax content of the Lillefrigg condensate is also
relatively high (4.9 wt. % for the fresh condensate).
Asphaltenes
The asphaltene content is generally low for the
Norwegian crudes. This is also the case with the
Fray crude ("hard asphaltenes: 0.20 wt% for the
fresh crude) and the Lillefrigg condensate ("hard
asphaltenes: 0.14 wt% for the fresh condensate). See
Figures A6.
The viscosity of the waterfree Lillefrigg condensate
is very low (2 cP 13°C ).
Flash point
All North Sea crudes including Fray, have flash
points higher than 60°C for the 200°C+ residues,
which corresponds to 12-24 hours weathering at sea
(see Figures A4). This is an important safety factor
since mechanically recovered emulsion with a flash
point lower than 60°C needs certified storage tanks
due to explosion hazard.
Flash points were not included in the limited study of
the Lillefrigg condensate.
Pour point
The pour point of fresh Fray crude is very high
(12°C) and in the same area as the test temperature
(13°C) of the emulsion and dispersability tests.
However, the pour point of the residues increases,
mainly due to the increase in concentration of heavy
waxes (see Figure A3). Fray residues have pour
points around 18 - 27°C and after several days at sea,
the oil may become semi-solid, particularly in winter
Interfacial tension
The interfacial tension between oil and sea water is
ranging from 24 to 34 mN/m for the fresh Fray crude
and residues. This is in the same range as other North
Sea paraffinic crudes. The interfacial tension is
lowered by photo-oxidation, and a drastic reduction is
observed compared to the topped residues which is
usual for the photo-oxidated oil samples.
Interfacial tension was not measured as a part of the
reduced study of the Lillefrigg condensate.
4.2
Water-in-oil emulsification
4.2.1
Rate of formation
The water uptake of the emulsions versus rotation
time at 13"C, is shown in Figure 4.2. The kinetics of
emulsion formation, expressed as t,,2-values, are
given in Figure 4.3. The water-in-oil emulsification
for the Fray residues is very rapid, and is similar to
other paraffinis crudes like Veslefrikkand Statfjord.
C B ~ ~
mmr a m o u r
Water content (~01%)
Figure 4.1
Viscosity ratio between w/o-emulsion and water-free parent oiUresidue a s a function of water
content of the FrQy crude.
The maximum water uptake measured in the
laboratory with the rotating flask apparatus (water
content in emulsion after mixing for 24 hours)
ranged from 77 to 90 vol.% for the different
residues. This water content was as expected from
the viscosity of the parent residues (see Figure 2.4).
between Fray and Lillefrigg. These results shows
that emulsions formed by the Lillefrigg condensate
are very unstable and these emulsions will settle out
all the water within 24 hours. The 75:25 blend has
emulsification properties more similar with the pure
Fray crude.
Different from most North Sea condensates does the
Lillefrigg condensate form wlo-emulsions. The
water uptake is also rapid probably due to the high
vax content, but the stability of the emulsions are
very low. Water is completely settled out of the
emulsion if energy is not applied to the emulsion
(see chapter 4.2 and Appendx B).
Emulsion breaking effectiveness was tested in this
project. The conditions used were:
4.2.2
The breaking effectiveness of the demulsifier is
given as fractional dehydration (D), as defined in
Appendix B.
Viscosity
Not all of the Fray oil wlo-emulsions had viscosity
ratios in accordance with the general curve
developed by Mackay (Figure 4.1). This indicates
that the Fray residues form less viscous emulsions
than expected according to accepted theory. The
maximum water emulsions with 150°C+ and
2W°C+ residues have a significant lower viscosity
ratio than expected. The viscosities measured in the
laboratory were used as input to IKUs Weathering
Model instead of the theoretical Mackay equation
used by most other oil spill models.
4.2.3
Stability
of
wlo-emulsions
effectiveness of emulsion breaker
The concentration of the demulsifier used was
500 and 2000 ppm of the oil volume.
The emulsion breaker was Alcopol 0 60%
and
The stabilities expressed as the degree of natural
dehydration during settling, of the wlo-emulsions of
different crude oil residues are shown in Figure 4.4.
Both the 150°C+ and the 200°C+ residue of Fray
form relatively unstable emulsions and releases
much of the water within 24 hours. This is most
unusual for most paraffinic crudes (e.g. Veslefrikk
and Statfjord). The napthenic Gullfaks shows
similar behaviour as the Fray crude. The other more
weathered residues form emulsions with higher
stability.
Corresponding results are given in Appendix B for
the Lillefrigg condensate and the 75:25 blend
The wlo-emulsions formed from the Fray residues
as from most North Sea crudes, are relatively easy
to break with Alcopol 0 60% (see figure 4.5). The
figure shows that the effectiveness of the emulsion
breaker depends upon the degree of weathering.
For most practical purposes is the small
effectiveness difference between 500 and 2000 ppm
neglectible and a low dosage rate of 500 ppm
should be selected during an oil spill recovery
operation with the Fray crude.
This is imprortant for calculating the storage
capasity for mechanically recovered wlo-emulsion
during an oilspill recovery operation. Figure 4.5
shows that upto 3-5 days of weathering (250°C+)
most of the water (upto 80-90%) in recovered wloemulsion can be settled out by demulsifier
treatment. This implies that the storage capasity of
recovered emulsion can be increase up to 4 times by
reducing the water content from 80 to 20% by
demulsifier treatment and disharging the water
being settled out of the emulsion.
In common with most other crude oils, the wloemulsion of the photo-oxidised Fray oil is less
effected by the emulsion breaker than the similar
non-photo-oxidised residue (250°C+).
10
15
Rotation time (hours)
Figure 4.2
Water content versus rotation time for the different weathered residues for the Fr@y crude.
Temperature: 13°C.
Oil residue
Figure 4.3
Water-in-oil emulsification kinetics expressed as tm-values for the different weathered
residues of the crudes at 13OC.
Heidrun
- o - Sture Blend
-a - Statfjord
- e- Gullfaks
15OoC+
2OO0C+
25OoC+
Oil residue
Figure 4.4
Dehydration of the w/o-emulsions (settling-period of 24 hours).
-...__
I
-
Fray 2000 ppm
-Fray
500 ppm
-+-Heidrun
-.+-. Sture Blend
- .. ..- Statfjord
.
--0--
.._
l
...,
'.__
..
W.
Gullfaks
I -..a...
Veslefrikk
X
I
2oO0C+
250°C+
Olje residue
Figure 4.5
Eficiency of Alcopol 0 60% (2000 ppm to the oil volume) in breaking do-emulsions
(dehydration of the do-emulsion over a settling-period of 24 hours after treatment with
demulsifier).
4.3
Chemical dispersability testing
The effectiveness of the dispersants varies over a
wide range with the IFP-method, a dispersability of
70-80% is considered to be a high effectiveness. The
dispersability of the wlo-emulsion is much lower (337%) compered to the waterfree oil residue.
Only the Fray crude was included in the screening
testing. Dispersability testing of the Lillefrigg
condensate and the 75:25 blend was perfomed only
on the 200"C+ residues and with the IFP test.
4.3.1
It is strongly emphasised that this limited screening
testing does not form any absolute ranking of
dispersants, trying to find the optimum product for
the Fray oil. However, it indicates of the variation in
relative performance among the most common
dispersants in contingency storage in Norway.
Initial screening of dispersants
Not all dispersants are equally effective against all
types of oil. Earlier studies (e.g. Brandvik et al.,
1990) have shown this. A screening study of
effectiveness of eight different dispersants, using the
IFP method on the 200"C+ residue of the Fray
crude, and emulsion with 50 vol.% water prepared
from this residue, was performed.
Based on these results, Corexit 9500 and Dasic NS,
two of the best products in the screening and also
commercially available, were selected for the further
dispersability testing of the Fray crude oil.
The results from this screening are presented in
Figure 4.6 and Table C1 in Appendix C. The results
are the average of three parallels.
100
I W200°C+ waterfree residue
1
200°C 50% emulsion
Dispolene
Corexit
Enersp
36s
9500
1037
IKU-9
lnipol IPC
Dasic
LTS
Dasic NS
OSR 5
Dispersants
Figure 4.6
Chemical dispersability (%) measured with the IFP-test on Fr@y crude (the 200°C+ and
200°C+/50% water emulsion) at 13°C with 8 different dispersants. DOR = 1/25.
4.3.2
Comprehensive dispersability testing of
the Fr0y crude
above 2-3000 cP the Fray crude oil is badly
dispersable, as assessed by the IFP method.
The second stage of this dispersability study was to
measure the effectiveness, by two different methods
(IFP and MNS), of two dispersants (Corexit 9500
and Dasic NS) on all the samples prepared from the
Fray crude oil (see figure 3.1).
The dispersants also produced high effectiveness (90
- loo%), with the MNS test method. The limiting
viscosity with the MNS test method was higher,
which is due to higher turbulence on the surface. The
effectiveness started to decrease when the viscosity
exceeded 1000 cP, and became half of the maximum
value when the viscosity was around 2-3000 CP. At
viscosities above 6000 cP is the Fray crude expected
to disperse very slowly and for practical purposes
regarded as being not dispersable, as assessed by the
MNS method.
The results are presented in the Figure 4.7. To
enable the trends to be seen more clearly, the IFP
and MNS effectiveness results are presented as a
function of the viscosity of the sample. The
effectiveness results and the median droplet size
values obtained for the dispersed residues, are also
listed in Tables C2 and C3 in Appendix C. The
results are the average of three (IFP) and two (MNS)
replicate tests (parallels).
Both dispersants gave a high effectiveness of about
60-70% (Figure 4.7) in the IFP tests, for residues
and emulsions with viscosities up to 200 CP. As the
viscosity increased the effectiveness dropped
gradually, reaching about half of the maximum
effectiveness at a viscosity of 1000 CP.At viscosities
It is difficult to precisely relate the energy used in
these laboratory test methods to windtwaveconditions at sea. However, it can be estimated that,
in a wind velocity of 5 - 10 d s , the Fray oil will be
dispersable up to a viscosity of about 6000 CP.
Due to the low stability of the wlo-emulsion at low
degree of weathering, the Fray crude is regarded as
higly dispersable at sea. This is not typical for a
crude with such a high vax content and also with
asphaltenelresins present, which usually forms very
stable wlo-emulsions and reduces the dispersebility.
I
0
IFP, Corexit 9500
o
-
MNS, Dasic-NS
P
H
-
*
I
I
r
l
.
l , , ,
100
1000
10000
100000
Viscosity (cP)
Figure
4.7
Effectiveness of the dispersing a enrs Corexit 9500 and Dasic NS versus viscosity of the rvaterfree residues (shear rate 1 0 0 S- ) and emulsions of d.rfferent water content (shear rate I 0 S - ' )
f
of the Fr@ycrude.
C_
Dispersability testing of the Lillefrigg
condensate and blends of F r ~ ycrude and
Lillefrigg condensate
the production from the Fray installation, while the
75:25 blend is more representative for a later level in
the production.
A limited dispersability testing of the Lillefrigg
condensate and two blends between Fray crude and
Lillefrigg condensate 5050 and 75:25 was
performed.
'This dispersability testing was performed only on
emulsion made from the 200"C+ residues, with the
dispersant Corexit 9500, and with the IFP-test. The
results are shown in figure 4.8 and follow the same
trends as shown in figure 4.7. These results show
that the Lillefrigg condensate and the blends of Fray
and Lillefrigg have a dispersability which is equal or
better than the Fray crude.
4.3.3
A blend of Fray and Lillefrigg is transported from
the Frigg installations to the Oseberg field. The
5 0 5 0 blend is representative for the first phase of
100
1000
10000
Viscosity (cP)
Figure 4.8
IF0 effectiveness of the dispersing agents Corexit 9500 versus viscosity of the water-free
residues (shear rate 100 S - ] ) and emulsions of d8erent water content (shear rate 10 S - ] ) of the
Fr#y crude, the Lillefrigg condensate and two blends (50:50 and 75:25) between these
products.
-..
s a m e onour
4.4
The meso scale flume test
4.4.1
Water uptake
from the F r ~ ycrude are relativelly stable after
approximattelly one day of weathering at sea.
The results from the water uptake measurements in
the meso-scale flume experiments are listed in Table
D2 in Appendix D.
The Fray crude oil emulsified fairly rapidly in the
flume with the maximum water content of 60% after
1 - 2 hours. The rate of water-in-oil emulsification in
the flume was however slower than the rate
measured with the rotating flasks in the laboratory.
The emulsions produced in the meso-scale flume are
likely to be more representative of those produced at
sea, in terms of their maximum water content and
stability, than those produced in the small scale
laboratory procedure. The rotating flask apparatus
may be slightly too energetic to accurately simulate
the emulsification process that occurs at the sea. The
maximum water content obtained in the flume (60%)
is therefore used to correct the maximum water
content measured with the rotating flask apparatus
(77-90%). A maximum wateruptake of 70 was
therfore used as the input to the numerical model
(Section 5).
4.4.2
Hovewer, figure D2 shows also that the demulsifier
treatment is still very effective on the F r ~ yemulsions
even after three days of weathering in the flume.
This is also in agreement with the stepwise
weathering observations (see figure 4.5).
4.4.4
Natural and chemical dispersability of
the Frey crude
The degree of natural dispersion for Fray crude is
relatively high initially and decreases towards the
end of the experiment. The results are displayed in
Table D3 and Figure D3, Appendix D. Most oils
show this decreasing degree of natural dispersion
with time, as the evaporative loss, increasing water
content and viscosity of the surface oil reduces the
formation of small oil droplets (approx. 1-70
microns) into the sea water.
HI
L.
m*
The chemical dispersability of the emulsion samples
were tested with Dasic NS using the IFP test. All the
surface samples from the flume were chemically
dispersable to some extent. In Figure D4, Appendix
D, the effectiveness results are shown and compared
to the results obtained from the stepwise weathering.
After weathering in the flume the wlo-emulsion was
dispersable at approximattelly the same viscosity
(-1000 cP) as the stepwise weathering, when assesed
with the IFP method.
Emulsion stability and effectiveness of
emulsion breaker
4.4.5
The emulsion stability (natural dehydration, D) and
the breaking effectiveness of the demulsifier Alcopol
0 60% on the wlo-emulsions, as function of
weathering time in the flume, are given in Figure D2.
'The results are also listed in the Table D2 in
Appendix D. The results are presented as fractional
dehydration of the emulsion, D (see Appendix B for
definition).
The emulsion samples of Fray taken after 1 - 5 hours
of weathering are totally unstable (D natural
1).
After this the emulsions became very stable (see
figure D2). Samples taken after 24 hours are
completely stable and do not loose any water after
settling for 24 hours, (D natural 0). This aggrees
with the observations from the stepwise weathering
study (see figure 4.4) and shows that emulsions made
-
-
--1
The results from the testing of natural and chemical
dispersability are listed in Table D3 in Appendix D.
The viscosities (at shear rate 10s-l) of the emulsions
are also listed in the table.
Viscosity of wlo-emulsion
The viscosity data for wlo-emulsions (Table D2,
Appendix D) are compared to predicted viscosity in
Figure 4.9b. There is a relatively good agreement
between measured viscosity and predicted viscosity
at 2 to 10 mls wind speed for the first 2 hours. After
that, the measured viscosities are lower than
predicted.
4.4.3
+.
Evaporative loss
The evaporative loss was calculated from the density
of the water free oil by using the IKU numerical
weathering model to predict a density that was only
dependant on evaporation. The evaporation results
are given in table D1, Appendix D and compared to
predicted evaporation in Figure 4.9a. From Figure
4.9.a it can be shown that the evaporation in the
flume was in relatively good agreement with the
predicted evaporation at 5 to 10 mls wind speed.
r
e
W
4.4.6
Oil adsorbed to the flume walls.
Oil removed by the sampling.
Mass balance
Figure 4.8 shows the mass balance for the Froy
crude oil in the meso-scale flume test. The major
elements of the mass balance for an oil spilt at sea
are :
The amounts of oil evaporated, dispersed and
sampled were calculatell, while the oil adsorbed to
the walls was estimated. At the end of the flume
experiment (72 hours), ca. 35% of the oil was
evaporated, ca. 1% was dispersed into the water
column, ca. 27% was removed by sampling and ca.
13% was adsorbed to the flume walls. The amount of
surface oil remaining at the end of the experiment
was calculated to be ca. 25% which is ca. 2.3 litres
of water-free oil, present as ca. 5.9 litres of w/oemulsion (based on a water content of 61%).
Evaporative loss of volatile components.
Oil remaining on the surface.
Oil dispersed (natural dispersion) into the water
column.
As the initial oil volume in the flume experiments is
relatively small (9 L), the following parameters also
have to be considered:
0
10
20
30
40
50
60
Time (hours)
Figure 4.8
Mass balance from the meso-scaleflume testing of the Fr@ycrude. Temperature: 13°C.
70
Wind Speed ( d s ) : 15
Wind Speed ( d s ) : 10
------
Wind Speed ( d s ) : 5
Wind Speed ( d s ) : 2
Sea surface temperature: 13'C
50
I
1
!L
Based on distillation data
-
40
S
--
-
U
0)
L.
2
I
30
>
I
-
W
I
20
-'
1
H
D
H
H
H
H
H
H
H
10
0.25
0.5
l
2
Hours
Figure 4.9
3
6
9
12
1
2
3
4
5
Days
Predictions of evaporation ( A ) and viscosity ( B ) based on 'Step-wise" laboratory
investigations, with a plot of the experimental values from the jlume experiments (FrQy
crude). The predictions are calculated with 13°C temperature and 2 mm constant film
thickness.
-.
S--
5.
PREDICTION OF PROPERTIES AT SEA
5.1
Introduction
relevant for other properties, such as viscosity and
pour-point. We have chosen a more direct empirical
approach, where laboratory measurements are the
basis for more accurate predictions (see section
5.1.1).
The efficiency of various oil spill combat methods
are known to depend to a large extent on the physical
properties of the oil. This is particularly true for
dispersant treatment, where increased viscosity due
to evaporation and w/o-emulsion formation may
make the oil resistant to dispersants within hours (or
days) after the oil is spilled. Reliable predictions of
the changing properties of the oil in variable sea
conditions are of great value in determining the time
window for efficient application of dispersants.
Similar limitations exist also for the efficiency of
other techniques such as e.g. burning and mechanical
recovery.
5.1.1
Numerical weathering model
The numerical weathering model developed at IKU
and used in this project is described in more detail in
Johansen, 1991 and Aamo et al. 1993 and in the
users guide for the model. The method uses the
properties of weathered oils subjected to a
standardised laboratory investigation of the crude
oil. This data is then used to predict evaporative loss
and wlo-emulsion formation under a chosen set of
sea conditions (sea state, sea temperature, oil film
thickness).
Different approaches to the oil property prediction
problem have been established in the literature. One
approach is to derive a set of mixing rules, where the
various physical properties of the oils are derived on
the basis of the changing composition of the
weathered oil. Simple mixing rules may be relevant
for the prediction of some of the properties such as
the density of the oil, but this approach is less
Figure 5.1 illustrates the experimental data input and
the predicted properties produced by the model,
which has been developed to run under Windows on
an IBM compatible personal computer.
IKU Oil
Weathering
Model
Laboratory data of fresh and
weathered oil samples:
Distillation curve (TBP)
Densities
Viscosities
Flash points
Pour points
Water uptake rates (to,s-values)
Maximum water uptake ability
Viscosity ratios
(wlo-emulsionlparentoil)
Viscosity limits for chemical
dispersion
Predicted oil properties by time at
chosen environmental conditions:
Evaporative loss
Density
Viscosity
Flash point
Pour point
Water content
Viscosity of wlo-emulsion
Natural dispersion
Total oil mass-balance
'Time window' for use of
dispersants and U&
burning
B
Criteria used
in the model
Environmental
conditions
(Wind speed, sea temperature,
oil film thickness)
I
Figure 5. I
Schematic diagram of the input data to the model and the predicted output oil properties.
"-.
nunr a m o u r
This procedure has been used in this manual to
predict the changing properties of weathered Fray
crude oil. It includes graphical charts to describe the
development of each property with time under a
chosen set of sea conditions (wind speeds) at both
summer (15°C) and winter (5°C) sea temperatures.
5.2
Criteria used for the predictions
5.2.1
Discharge conditions and time-scale for
predictions
window" where an oil spill combat operation is
feasible:
Windspeed=2m/s:
Beaufort wind 2 (light breeze, 0.1 - 0.3 m wave
height.
Wind speed = 5 mJs:
Beaufort wind 3 (gentle to moderate breeze),
0.5 - 0.8 m wave height.
Windspeed=lOm/s:
Beaufort wind 5 (fresh breeze), 1.5 - 2.5 m
wave height.
The graphical charts present the predictions of
various physical properties of the oil over a period
from 15 min. to 5 days after discharge. This covers
potential spill situations where it may be possible to
act within a very short response time such as spills
close to terminals, but also includes offshore spills
where the response may take several days.
Wind speed = 15 mls:
Beaufort wind 6 - 7 (strong breeze 1 moderate
gale), 3 - 4 m wave height.
5.2.4
5.2.2
Realistic computations of the evaporative loss in
various field conditions form the basis for the
modelling of the oil parameters. The change of the
evaporative loss with time depends on the original
composition (i.e. distillation curve) of the oil, sea
temperature, wind speed. It is also sensitive to the
initial surface concentration of oil, and this change
due to sprdading. This means that the change in oil
properties shortly after discharge will depend on the
discharge conditions e.g. sub-sea and surface blowouts, tanker spills, pipeline leakage etc.
In this manual we have chosen a surface release
scenario with exponential decay of the film
thickness:
20 mm
2 mm
l hour
5°C - sea temperature in the winter time.
15°C - sea temperature in the summer time.
These are typical of sea temperatures that may be
encountered in the North Sea and Haltenbanken. The
lowest and highest surface water temperature
measured at the Statfjord field from 1978 to 1986
were 5.4OC and 16S°C, respectively. Oil spill
countermeasures will be more difficult at lower sea
temperatures than at higher temperatures.
5.2.5
Open sea: If the flash point of the spilled oil is
close to or below the ambient sea temperature,
the oil will pose a fire hazard.
Recovered oil in confined air space: If the flash
point of the mechanically recovered oil or wloemulsion, is less than 60°C, explosion-proof
recovery equipment I shipboard tankage will
have to be used.
Wind and sea state conditions
The prevailing weather conditions will greatly
influence the oil weathering rate. There is a close
correlation between wind speed and significant wave
heights. The predictions are based on four different
wind speeds which represent a span of the "weather
Fire and explosion hazard
The flash point is the lowest temperature at which
the gas or vapour generated by an oil can be ignited
by a flame. The flash point criteria (EPA, 1982)
chosen for the predictions are:
This produces a time development which is highly
comparable to that observed in an experimental field
trial at Haltenbanken in 1989 (Johansen, 1991). The
samples taken for assessment of physical properties
were taken in the thicker part of the experimental oil
slick.
5.2.3
Sea temperatures
In these predictions, two different temperatures have
been specified:
Oil film thickness
Initial film thickness:
Terminal film thickness (wlo-emulsion):
Half-time in film thickness reduction:
I
5.2.6
Laboratory investigation
The majority of the weathering properties of the
crude used in the PC model were obtained using
e
small scale laboratory methodology. An exception is
the maximum water uptake ability, where the small
scale results have been adjusted with the results
obtained in the meso-scale flume tests. The
maximum water content of the emulsion produced by
small scale testing was higher than that obtained
from the meso-scale testing. The viscosity of the
wlo-emulsion depends on the water content, as
described in section 2.7.3. Using the water content
obtained in the small scale testing, would have
predicted unrealistically high emulsion viscosities.
Criteria for the chemical dispersability of the oil:
From the extensive testing of dispersability, the
following criteria have been chosen for the
dispersability of the Fray oil as a function of the
viscosity of the oil or wlo-emulsion (measured at
shear rate 10 S-'):
Up to 1000 cP:
m
m
The oil is easily dispersible
used by the Norwegian oil companies (NOFO) have
proved to be capable of coping with more viscous
material even above 100 000 CP.
5.3
Examples of how the prediction tables may be used
are given below:
Scenario 1:
An oil spill from the Fray field has drifted for about
24 hours. The weather conditions in this period have
been the following:
Wind: 2 to 3 m/s
Sea temperature: approx. 15OC.
Using the prediction tables, the properties of the oil
after weathering for 24 hours will then
approximately be:
1000 to 6000 cP: The oil has reduced
dispersability
Above 6000 cP:
The oil is badlv/slowlv
dispersible.
m
m
m
The pour point criteria were detected on the
following basis:
m
Up to 5°C higher than sea temperature:
The oil is disversible.
m
In the area 5°C to 15°C above the sea
temperature:
The oil has reduced dispersability.
m
5.2.7
More than 15°C higher
temperature:
The oil is badlv dispersible.
than
the
sea
Optimised mechanical recovery
Field exercises performed in Norway in recent years
have revealed that the efficiency of a mechanical
recovery operation increases if the viscosity of the
oil or the oiltwlo-emulsion is higher than 1000 CP.
This is due to the fact that low viscosity oil or
emulsion leak under the booms. Therefore, 1000 cP
has been used as a lower viscosity limit for an
optimal mechanical oil spill combat operation.
viscosity limit for mechanical recovery,
The
depends on the type of skimmer used. For some discskimmers, the recovery rate decreases significantly if
the wlo-emulsion viscosity is higher than 10 000 cP
(ITOPF, 1986). However, large "TransrecM-systems
Prediction tables-user examples
Degree of evaporation:
Flash point:
Pour point:
Water content:
The viscosity of the emulsion:
30%
l 10°C
25-27°C
65 vol%
4000 CP.
The wlo-emulsion has a reduced dispersability due to
the high viscosity and pour point, but are still
dispersabile. The viscosity is above the lower
viscosity limit for optimum mechanical recovery
(1000 cP) and most disc and rope skimmers will be
expected to have a high effectiveness.
Scenario 2:
The Fray oil has drifted for about 6 hours. The
weather conditions in this period have been the
following:
Wind: 10 m/s
Sea temperature: approx. 15OC.
The properties of the weathered oil will then
approximately be:
m
m
Degree of evaporation:
Flash point:
Pour point:
Water content:
The viscosity of the emulsion:
30%
l 10°C
25°C
70 vol%
2000 CP.
The wlo-emulsion may show reduced dispersability,
but dispersants will probably be effective due to the
wind speed. The viscosity for the oil-in-water
emulsion is also above the lower limit for optimum
mechanical recovery (1000 cP).
Scenario 3:
The Fray oil has drifted for about 24 hours. The
weather conditions in this period have been the
following:
Wind: 15 to 18 m/s (Significant wave height >3m)
Sea temperature: approx. 5OC.
The properties of the oil will approximately be:
a
a
Degree of evaporation:
Flash point:
Pour point:
Water content:
The viscosity of the emulsion:
39%
150°C
32°C
70 vol%
30 000 CP.
The effectiveness of dispersants would be expected
to be very low and dispersants should not be used
due to the high viscosity and the high pour point of
the emulsion. Application of dispersant in such high
winds is also difficult due to wind drift of the
dispersant and constantly overwashing of the surface
oil with sea water.
The waves may be so high that they cause problems
to mechanical recovery on the other side will the
high sea state increase the natural dispersion of the
oil slick (as much as 50-60% of the oil could be
expected to be naturally dispersed after 24 hours).
The rate of natural dispersion will also be very
dependant of the release conditions.
L*,.A
. .,
mmr a m o u r
5.
PREDICTED PROPERTIES AT SEA
5.4
Fray crude, list of prediction tables (pink pages):
5.5
Lillefrigg condensate, list of prediction tables (blue pages):
5.6
Fray and Lillefrigg blend (75:25), list of prediction tables (brown pages):
Property: EVAPORATIVE LOSS
Oil m e : FROY
Description: North Sea crude from the Frsy field (ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (nun) : 2
Halftime in thickness reduction (hrs):
Pred. date: May. 10
Wind Speed
Speed
Speed
Speed
--- Wind
-- ----- -.
- - Wind
Wind
1.0
I
(m/s): 1 5
(m/s): 10
(m/s): 5
( m / ~: )2
Winter Conditions ( 5 OC)
I
Hours
I
Days
Summer conditions (15 OC)
- Based on distillation data
40
/GS-cc- - -@ccL
/ -
c
-
h
8
p
.
- -.---
I~
c #
V
-
*----
d
4<0 - -.--
30
Mc /
-
C,
Id
&
;
20
3
W
0
/ 0 0
A
-
4
'
/
I
/
0
I
_
-c-- - -_ - - - -
10
0
C
.
H # H r
C
c
C
_.----
C
*
*
0
I
v 0
0 /
H
/
C
C
*#
0
I
*--
C
c c e
c
0
0.25
I
I
0.5
1
2
Hours
3
6
9
12
1
Days
2
3
4
5
Property: WATER CONTENT
Oil Type: FROY
Description: North Sea crude from the Fray field (ELF)
Data Source: IKU Petroleum Research (1996)
1
Copyright 1996
Oil film thickness:
Initial ( m ): 20
Terminal (mm): 2
Halftime in thickness reduction (hrs):
1
Pred. date: May. 10
---
---------a
I
I
Wind
Wind
Wind
Wind
Speed
Speed
Speed
Speed
1.0
(m/s): 15
(m/s): 10
(m/s): 5
(m/s): 2
Winter Conditions (5 OC)
Hours
Days
Summer Conditions (15 OC)
I
Hours
Days
Property: VISCOSITY OF EMULSION
Oil Type: FROY
Description: North Sea crude from the Fray field (ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 2
Halftime in thickness reduction (hrs):
Pred. date: Aug. 1,
Wind Speed (m/s):
(m/s):
(m/s):
(m/s):
-- Wind
Speed
----.
Wind Speed
- - - - - - Wind Speed
15
10
5
2
7-
1.0
Chemically dispersable (c1000 cP)
Reduced chemical dispersability
Not chemically dispersable (>6000 cP)
Hours
Based on viscosity measurements carried out at a shear rate of 10 reciprocal seconds.
Chemical dispersability information based on experiments under standard laboratory
conditions.
Property: NATURAL DISPERSION
Oil Type: FROY
Descrigtion: North Sea crude from the Fray field (ELF)
Data source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 2
Halftime in thickness reduction (hrs):
Pred. date: May. 10
Wind Speed
Speed
Speed
Speed
--- Wind
Wind
- - - - - - Wind
- - - - m
1.0
(m/s): 15
(m/s): 10
(m/s): 5
(m/s): 2
Winter Conditions ( 5
OC)
70
60
n
50
ov
U
aQ)
40
E 30
9
-4
Q)
n
20
//
10
0
-
00.25
___
0.5
1
2
3
6
9
12
Hours
I
I
I
----- --
C C
'C
C
C
1
2
I
3
4
5
Days
Summer Conditions (15 OC)
Hours
Days
The algorithm for prediction of natural dispersion is preliminary and is currently under
improvement.
I
Property: MASS BALANCE
Oil Type: FROY
~escription: North Sea crude from the Frsy field (ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 2
Halftime in thickness reduction (hrs):
Pred. date: May. 10
BNaturally
I
1.0
dispersed
Temperature: 15 OC
Hours
Wind speed: 10 m/s
Days
I
,
Temperature: 15 OC
I-
Hours
Wind speed: 1 5 m/s
Days
The algorithm for prediction of natural dispersion is preliminary and is currently under
improvement.
I
Property: POUR POINT FOR WATER-FREE OIL
Oil Type: FROY
Description: North Sea crude from the Fray field (ELF)
Data Source: II(U Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal ( m ): 2
Halftime in thickness reduction (hrs):
Pred. date: Mzy. 10
---
------
- - - - S
Wind
Wind
Wind
Wind
Speed
Speed
Speed
Speed
11-
(m/s): 15
(m/s): 10
(m/s): 5
(m/s): 2
1.0
Chemically disperable
Reduced chemical dispersability
~ o chemically
t
dispersable
m
Winter Conditions (5 OC)
- Based
Hours
Days
Hours
Days
on pour point measurements of weathered, water-free oil residues.
I
I
1
I
Property: FLASH POINT FOR WATER-FREE OIL
oil Type: F m
Description: North Sea crude from:the Fray field (ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 2
Halftime in thickness reduction (hrs):
Pred. date: May. 10
Wind
Wind
Wind
Wind
- - - - S
-
0.25
I
1
Speed
Speed
Speed
Speed
(m/s): 15
(m/s): 10
(m/s): 5
(m/s): 2
0.5
1
[
No
I
fire hazard
1-
2
Fire hazard in tankage (c60 O C )
Fire hazard at sea surface (below sea temper
3
6
9
12
Hours
1
2
3
4
5
Days
C
I
Summer Conditions (15 OC)
200
U
'I
1.0
0
-
I
I
I
Based on lab weathering data
150
-
E:
-G
l0C
P1
9Id
I
g
50
3
I
I
!
0
0.25
II
0.5
1
2
Hours
3
6
9
12
1
Days
Based on flash point measurements of weathered, water-free oil residues.
2
3
4
5
Property: VISCOSITY FOR WATER-FREE OIL
Oil Type: FROY
Description: North Sea crude from the Frny field (ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 2
Halftime in thickness reduction (hrs):
Pred. date: May. 10
Speed
--- Wind
Wind Speed
Wind Speed
- - - - - - Wind
Speed
- - - - - a
(m/s): 15
(m/s): 10
(m/s): 5
(m/s): 2
1.0
Chemically dispersable (<l000 cP)
v]
Reduced chemical dispersability
~ o chemically
t
dispersable (>G000 cp)
Winter Conditions (5 OC)
0.25
0.5
1
2
3
6
9
12
Hours
1
2
3
4
5
2
3
4
5
Days
Summer Conditions (15
OC)
10000
A
Pc
U
1000
U
$1
L,
-l4
U)
0
U
-4
>
100
-g
- --
c-- - H 0
-
-
C C C
*
C
-
-
-
0
C
/
H/-
H
0
0
0
*-**
-
-_-----'
10 ,
0.25
0.5
1
2
Hours
3
6
9
12
1
Days
Based on viscosity measurements carried out at a shear rate of 100 reciprocal seconds.
Chemical dispersability information based on experiments under standard laboratory
conditions.
Property: DENSITY OF EMULSION
Oil Type: FROY
Description: North Sea crude fr& the Fray field (ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 2
Half time in thickness reduction (hrs):
Pred. date: May. 10
---- . Wind
Speed
Wind Speed
.I- - - - - - Wind Speed
I
I
I
1-1
v
(m/s): 10
(m/s): 5
(m/s): 2
1.0
i
Oil stays on surface ( 4 0 2 5 gm/l)
oil sinks (>l025 gm/l)
Winter Conditions ( 5 OC)
I
Summer Conditions (15 OC)
I
Hours
Days
I
Property: EVAPORATIVE LOSS
Oil Type: LILLEFRIGG
~escrigtion: Condensate from the LilleFrigg field (ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 0.2
Halftime in thickness reduction (hrs):
Pred. date: May. 10
Wind Speed
Speed
Speed
Speed
--- Wind
Wind
- - - - - - Wind
- - - - S
1.0
(m/s): 15
(m/s): 10
(m/s): 5
(m/s): 2
p
p
p
-
P
p
-
Winter Conditions (5 OC)
I
I
Hours
Days
I
Summer Conditions (15 OC)
.-
-
I
I
I
-
Based on distillation data
60
* c.
-_
-----/
I
-
)C*#
50
/ 4-
-
0
0
0
-
40
-
.'
0 -
30
20
/
0
'
0
I
0
0
- _----_ - - - - - -- - - - "
cc-
#
F
0
0
#
#
#
c-
fl
-
0
c - - -
0
0.25
0.5
1
2
Hours
3
6
9
12
1
Days
2
3
4
5
Property: WATER CONTENT
Oil Type: LILLEFRIGG
Description: Condensate from the LilleFrigg field (ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 0.2
Halftime in thickness reduction (hrs):
Pred. date: May. 10
Wind
Wind
Wind
Wind
------v
- m - - - -
Speed
Speed
Speed
Speed
1.0
(m/s): 15
(m/s): 10
(m/s): 5
(m/s): 2
Winter Conditions ( 5 OC)
80
I
I
I
- Based on lab weathering data
-
-
#
, C 0
0
2
60
W
-
A
/-
L,
/
-,
0
0
-
k
-
3
0)
20
-
I
0
0
0
/
/
0
/
0
/
d 40
U
0
0
/
-
L,
g
-_____-------..--------
#
/
0
0
0
0
0
R
/
fi
0
0
0
0
R
0
,-M
d
C
C
C
--
e
C
_ * - - C
0
0.25
0.5
1
2
3
9
6
12
Hours
1
2
3
4
5
2
3
4
5
Days
Summer Conditions (15 OC)
80
L
C
--
*
#
A
d
e
V
60
-
4J
3
/
/
-
#
0
-
a,
/
g
/
/
/
0
/
/
0
/
0
0
0
/
0
0
-
L,
0
0
0
20-;
4
-
--
0
0
0
0
E: 40
k
0
0
L,
-
-----
0
B
-
0
0
C
0
P
C
#
---
C
c - -
0
0.25
I
0.5
1
2
Hours
3
6
9
12
1
Days
Property: VISCOSITY OF EMULSION
Oil Type: LILLEFRIGG
Description: Condensate from the LilleFrigg field (ELF)
Data Source: IKU Petroleum. Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm) : 20
Terminal (mm): 0.2
Halftime in thickness reduction (hrs):
Pred. date: Aug. 1,
1.0
Wind Speed (m/s): 15
(m/s): 10
(m/s): 5
(m/s): 2
--- Wind Speed
-- - -. Wind Speed
- - - - - - Wind Speed
Winter Conditions (5 OC)
10000-
I
I
-
m
R
,
-/cc-
- H H
* -g
0
-d
-
$(
100-
m
--
3
10-
m
C L'
e
--
U
--- ---,
1000-
U
L,
Based on lab weathering data
-
P4
*r(
I
I
0
0
rl
/V
c
'
_ :- ------- -_ - - - - - -
.-
C
1
/
m e - - -
C - 0 -
C
C
H @ -
-
1
0.25
I
0.5
1
2
6
3
9
12
1
Hours
-
I
I
I
3
4
5
Days
Summer Conditions (15 OC)
1000-
2
Based on lab weathering data
c c C
-
/
-
y&--,7
C
-
C
C
--L
-c
C
'
h
%
V
$(
+1
-rl
V1
0
0
m
-rl
100-
-
0
0
'
10
3
0
'
#
#
- 0 -
-
- - - - # - - - - - C
m - - - - - -
m
1
0.25
I
0.5
1
2
Hours
3
6
9
12
1
2
3
I
4
t
5
Days
Viscosities at 10 and 15 m/s are not meaningful after 12 and 6 hours due to expected lack
of surface emulsion. This is caused by a high degree of evaporation and natural dispersion
( s e e mass balance sheets).
Property: NATURAL DISPERSION
Oil Type: LILLEFRIGG
Description: Condensate from the LilleFrigg field (ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 0.2
Halftime in thickness reduction (hrs):
Pred. date: May. 10
Wind Speed
Speed
Speed
Speed
--- Wind
Wind
- - - - - - Wind
- - - - S
(m/s):
(m/s):
(m/s):
(m/s):
1.0
15
10
5
2
Winter Conditions (5 OC)
70
60
X
50
Y
aQ)
V1
&
Q)
Pr
/
/
40
0
0
4
-
0
0
30
/
-
V1
-rl
/
Q 20
10
-----
/
-
L
0.5
1
0
0
4
0
I
r f l /
M/
-
2
0
0
/
I
-
0.25
0
0
1
-
03-
I
-
W
-
_ _ _ _ - - - m - - - -
*
3
6
9
12
1
Hours
2
3
4
5
Days
Summer Conditions (15 OC)
70
l
I
I
- Based on preliminary algorithm
60
n
X
50
-
Y
aQ)
I
40
Q)
9
-rl
n
t
/
r
I
V1
&
--
. C - - - - - - -
/
/
0
/
30
/
0
0
/
-
.
0
0
0
0
20
-
/
f
/
0 0
0
10
/
/
0
0.25
-
0.5
l
2
Hours
3
0
-
-
-
W
/
---
-
6
9
12
l
- - - , - - - - - - - - -
2
3
4
5
Days
The algorithm for prediction of natural dispersion is preliminary and is currently under
improvement.
Property: MASS BALANCE
Oil Type: LILLEFRIGG
Description: Condensate from the LilleFrigg field (ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 0.2
Halftime in thickness reduction (hrs):
Pred. date: May. 10
1.0
BEvaporated
Surf ace
Naturally dispersed
Temperature: 15 "C
0.25
0.5
1
2
3
Wind speed: 10 m/e
6
9
12
Hours
0.5
1
2
Hours
2
3
4
5
2
3
4
5
Days
Temperature: 15 OC
0.25
1
3
Wind speed: 15 m/s
6
9
12
1
Days
The algorithm for prediction of natural dispersion is preliminary and is currently under
improvement.
Property: POUR POINT FOR WATER-FREE OIL
Oil Type: LILLEFRIGG
Descriptions Condensate from the Lille~riggfield (ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 0.2
Halftime in thickness reduction (hrs):
Pred. date: May. 10
------ - - - v
Wind
Wind
Wind
Wind
Speed
Speed
Speed
Speed
1.0
7)
Chemically disperable
(m/s): 15
(m/s): 10
(m/s): 5
(m/s): 2
1-
Reduced chemical dispersability
j- >.......... ........ ........ Not chemically dispersable
60
h
U
0
V
40
U
d
-rl
0
P4
k
=1 20
0
P4
0
0.25
0.5
2
1
Hours
3
6
9
12
1
2
3
4
5
Days
Hours
Based on pour point measurements of weathered, water-free oil residues.
I
Propertyr FLASH POINT FOR WATER-IPREE OIL
Oil Type: LILLEFRIGG
Description: Condensate from the ~ i l l e ~ r i gfield
g
(ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 0.2
Halftime in thickness reduction (hrs):
Pred. date: May. 10
---
------ - - - m
Wind
Wind
Wind
Wind
Speed
Speed
Speed
Speed
(m/s):
(m/s):
(m/s):
(m/s):
1.0
7)
No fire hazard
15
10
mFire hazard in tankage (<G0 CC)
mFire hazard at sea surface (below sea temper
5
2
Winter Conditions (5 OC)
Hours
Days
Summer Conditions (15 OC)
0.25
0.5
1
2
Hours
3
6
9
12
1
Days
Based on flash point measurements of weathered, water-free oil residues.
2
3
4
5
Property: VISCOSITY FOR WATER-FREE OIL
Oil Type: LILLEFRIGG
Description: Condensate from the ~ i l l e ~ r i gfield
g
(ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 0.2
Halftime in thickness reduction (hrs):
Pred. date: May. 10
Wind Speed
Speed
Speed
Speed
--- Wind
Wind
- - - - - - Wind
- - - - S
1.0
(m/s): 15
(m/s): 10
(m/s): 5
(m/s): 2
Winter Conditions (5 OC)
10000
I
I
-
I
Based on lab weathering data
-
---
ed
,H4
--- -
C
, C d
C C
1000
C5
a(
0
U
$1
U
.
V)
0
0
P1
-r(
b
-
-.
100-
-
0
J
10
e
-L - - - - - - - - - - _-c--
1
0.25
-
H -
--e-
C
-
0'-.'
0
I
l
0.5
1
2
3
6
9
12
Hours
1
2
3
4
5
Days
Summer Conditions (15 OC)
10000
I
-
h
Pc
U
Y
$1
I
I
Based on lab weathering data
_ - - - -- ,---/
1000
-
C C - -
100-
V)
0
0
V)
rl
*
-
/
10-
-S-/-'---
----__ _
- - ---c
H
- - - C
_ _ - - - a
-
1,
0.25
l
0.5
1
2
Hours
3
6
9
12
1
2
3
4
Days
Based on viscosity measurements carried out at a s h ~ a rrate of 100 reciprocal seconds.
5
Property: DENSITY OF EMULSION
Oil Type: LILLEFRIGG
Description: Condensate from the LilleFrigg field (ELF)
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 0.2
Halftime in thickness reduction (hrs):
Pred. date: May. 10
---
---------S
Wind
Wind
Wind
Wind
Speed
Speed
Speed
Speed
11-
(m/s): 15
(m/s): 10
(m/s): 5
(m/s): 2
1.0
Oil stays on surface ( 4 0 2 5 gm/l)
oil sinks (,l025 gm/l)
Winter Conditions (5 OC)
0.25
1
0.5
2
3
6
9
12
Hours
1
2
3
4
5
2
3
4
5
Days
Summer Conditions (15 OC)
-82 5-
0
4
C
C
0.25
0.5
*
C
1
2
Hours
3
6
9
12
1
Days
L
Property: EVAPORATIVE LOSS
Oil Type: IPR0Y:LILLEFRIGG 75:25
Description: Blend of Fr0y:LilleFrigg (75:25) transport
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 1
Halftime in thickness reduction (hrs):
Pred. date: May. 10
r
Wind Speed (m/s):
(m/s):
(m/s):
Wind Speed (m/s):
--- Wind
Speed
Wind Speed
------
- - - w e
0.25
0.5
1.0
15
10
5
2
winter conditions (5 OC)
1
2
3
6
9
12
1
Hours
Days
Hours
Days
2
3
4
Property: WATER CONTENT
Oil Type: FR0Y:LILLEFRIGG 75:25
Description: Blend of Fr0y:LilleFrigg (75:25) transport
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 1
Halftime in thickness reduction (hrs):
Pred. date: May. 10
Wind Speed
Speed
Speed
Speed
--- Wind
Wind
- - - - - - Wind
----a
(m/s):
(m/s):
(m/s):
(m/s):
1.0
15
10
5
2
Winter Conditions (5 *C)
80
I
-
I
I
Based on lab weathering data
/
-
4~
C & & -
d#
-
A
0
-- ---
m--
0 -
0
0
,
0
f
/
p-1
--r
--'I
e
c---'
0
0
0
/
d'
/
0
0
0
4
0
0
0
d
-
0
e
#
H H @ #
e
0 - c
_-----
0
0.25
e
c-ce----
1
0.5
6
3
2
9
1
12
Hours
2
3
4
5
3
4
5
Days
Summer Conditions (15 OC)
80
I
1
I
- Based on 1
8
m
& #
60
-
Y
/
0
k
Q)
U
g
/
/
.-
- /
0
-
#
/
0
f
/
0
/
0
I
0
0
# /
0
e
0
H @ /
- ---'-.---.c---
0.5
0
0
0
/
0
0.25
0
0
0
/
c
0
0
0
-
0
0
/
/
20
0
/
/
-
# - - - - -
,m-
0
0
0 -
-
*
0
e
0
0
2
1
Hours
3
6
9
12
1
Days
2
Property: VISCOSI'ICY OF EMULSION
Oil Type: FR0Y:LILLEFRIGG 75:25
Description: Blend of Fr0y:LilleFrigg (75:25) transport
Data Source: IKU Petroleum Research (1996)
Oil film thickness:
Initial (nun): 20
Terminal (mm): 1
Halftime in thickness reduction (hrs):
---
R
Wind
Wind
Wind
Wind
------ - - - a
Speed
Speed
Speed
Speed
I
Copyright 1996
Pred. date: May. 10
1.0
(m/s): 15
( m / ~:) 10
(m/s): 5
(m/s): 2
Winter Conditioas (5 OC)
10000-
r'
--
-
-
$
I
1
--=-
Based on lab weathering data
-
D
U
I
.-0-
I
l000-
-
0
I
4
0
r
0
0
I
dP
0
0
0
0
I
I
I
0
I
l00
,
I
I
3
0
0
0
0
@ H 0
----
l0
0.25
C I
-.--*
-
0
0
0
- 0 . -
0.5
1
2
l
II
0
00
JJ
I
m - - - -
I 0
$1
b
.
I
--.--,-
D _ -
0
6
3
9
12
1
Hours
2
3
4
5
I
Days
I
I
W
Suxnner Conditions (15 OC)
h
Pc
U
U
h
.
L,
m
0
U
m
.rl
3
I
1
-
I
Based on lab weathering data
- /
1000
r
0
0
-
#
0
4*
-
0
0
0
-
0
-
C
0
I
0
I'
100-
-
0
I
0
I
0
I
0
I I
I
I
0
@@cC M
0
-.
10 .-- -
0 . -
1
0.25
I
0.5
1
2
Hours
3
6
9
12
1
2
3
4
Days
Based on viscosity measurements carried out at a shear rate of 10 reciprocal seconds.
5
Property: NATURAL DISPERSION
Oil Type: FROYsLILLEFRIGG 75:25
Description: Blend of Fr0y:LilleFrigg (75:25) transport
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 1
Halftime in thickness reduction (hrs):
Pred. date: May. 10
-----------a
Wind
Wind
Wind
Wind
Speed
Speed
Speed
Speed
(m/s):
(m/s):
(m/s):
(m/s):
1.0
15
10
5
2
Winter Conditions (5 OC)
70
60
n
50
b
V
aQ)
E
Q)
a
U
-4
/
40
/
-
/
/p
l
30
/
#'
20
-
./
1
10
------- -
M'4
0
0.25
/
r
l=-------
0. 5
1
2
3
6
9
12
C
Hours
#
e C C
- C - -
1
-
2
3
4
5
Days
Summer Conditions (15 OC)
70
I
1
I
- Based on preliminary algorithm
60
ic
-
n
8
V
aQ)
VI
k
Q)
9
-rl
50
-
/
/l
40
-
//
/l
30
-
/
/
Q 20
c
-
0
10
/
-
r
@
c-@
0
0.25
I
0.5
1
2
Hours
3
6
9
12
1
2
3
4
5
Days
The algorithm for prediction of natural dispersion is preliminary and is currently under
improvement.
Property: MASS BALANCE
Oil Type: FR0Y:LILLEFRIGG 75:25
~escription: Blend of ~rey:~illeFrigg(75:25) transport
Data Sourcer IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm) : 1
Halftime in thickness reduction (hrs):
Pred. date: May. 10
-
1.0
-pp
Evaporated
Surface
BNaturally dispersed
Temperature: 15 O C
=Ours
Wind speed: 10 m/s
I
Days
d
m
I
Temperature: 15 OC
Hours
Wind speed: 15 m/s
Days
The algorithm for prediction of natural dispersion is preliminary and is currently under
improvement.
I
I
I
Property: POUR POINT FOR WATER-FREE OIL
Oil Type: FR0Y:LILLEFRIGG 75:25
Description: Blend of Fr0y:LilleFrigg (75:25) transport
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 1
Halftime in thickness reduction (hrs):
Pred. date: May. 10
Speed
--- Wind
Wind Speed
Wind Speed
------ Wind Speed
- - - - S
1-
(m/s): 15
( m / ~ ) 10
:
(m/s): S
(rn/s): 2
1.0
mChemically
Reduced
~
disperable
dispersability
Not chemically dispersable
~
Winter Conditions (5 O C )
40
h
U
0
U
U
d
-4 20
0
PI
l4
g
PI
0
0.25
0.5
1
2
3
6
9
12
Hours
1
2
3
4
5
2
3
4
5
Days
40
n
U
0
U
JJ
E:
-4 20
0
Pc
k
g
PI
-
0
0.25
0.5
1
2
Hours
3
6
9
12
1
Days
Based on pour point measurements of weathered, water-free oil residues.
*
Property: FLASH POINT FOR WATER-FREE OIL
Oil Type: FR0Y:LILLEFRIGD 75:25
~escrigtion: Blend of Fr0y:LilleFrigg (75:25) transport
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 1
Halftime in thickness reduction (hrs):
Pred. date: May. 10
1-
Speed (m/s): 15
--- Wind
Wind Speed (m/s) 10
- - - -. Wind
Speed (m/s) 5
Wind Speed (m/s) 2
No fire hazard
mFire hazard in tankage (<G0
:
OC)
Fire hazard at sea surface (below sea temper.
:
:
- W - - - -
1.0
Winter Conditions (5 OC)
Hours
Days
Summer Conditions (15 OC)
200
150
h
U
0
U
,J
100
d
.l4
0
PI
5rd
50
FI
Crc
0
-50
0.25
0.5
1
2
Hours
3
6
9
12
1
Days
Based on flash point measurements of weathered, water-free oil residues.
2
3
4
5
Property: VISCOSITY FOR WATER-FREE OIL
Oil Type: FR0Y:LILLEFRIGG 75:25
Description: Blend of Frsy:LilleFrigg (75:25) transport
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 1
Halftime in thickness reduction (hrs):
Pred. date: May. 10
Speed
--- Wind
Wind Speed
----. Wind Speed
- - - - - - Wind Speed
(m/s):
(m/s):
(m/s):
(m/s) :
1.0
15
10
5
2
Winter Conditions (5 OC)
1000-
I
-
I
I
Based on lab weathering data
-
-4 --.
h
V
W
-
4---CC---or.----
l00-
-
-
h
-
U
0
.rl
U1
-
3
-
0
.- ------ _..--
1
0.25
0.5
1
2
3
@H*.-,----
-
6
9
12
1
2
3
4
5
2
3
4
5
Days
Hours
S u m e r Conditions (15 OC)
1000-
-
I
I
I
Based on lab weathering data
h
h
C,
3
-
-
1
0.25
0.5
1
2
Hours
3
6
9
12
1
Days
Based on viscosity measurements carried out at a shear rate of 100 reciprocal seconds.
Property: DENSITY OF EMULSION
Oil Type: FR0Y:LILLEFRIDG 75:25
Description: Blend of ~ r e y : ~ i l l e ~ r i g(75:25)
g
transport
Data Source: IKU Petroleum Research (1996)
Copyright 1996
Oil film thickness:
Initial (mm): 20
Terminal (mm): 1
Halftime in thickness reduction (hrs):
Pred. date: May. 10
--- - - - a
- - - - m -
Wind
Wind
Wind
Wind
Speed
Speed
Speed
Speed
1
(m/s): 15
(m/s): 10
(rn/s): 5
(m/s): 2
1.0
7
1-1
Oil stays on surface (c1025 gm/l)
Oil sinks (>l025 gm/l)
Winter Conditions (5 OC)
0
-/
875
4
-850iL---------
/
/
fl
e
/
#
I---
825
0.25
0
W
_-----
# - - - C
I
0.5
1
2
Hours
3
6
9
12
1
Days
2
3
4
5
SUMMARY OF THE WEATHERING PROPERTIES OF FR0Y CRUDE
AT SEA
These conclusion are based on the laboratory investigations described in Section 4 and on the modelling
predictions from Section 5. Generally are the weathering values given for a temperature of 13OC and 5 mls wind.
A.
Chemical properties
Frgy is a paraffinic crude with a high vax content (5.1 wt.% in the fresh crude).
High saturate content (approx. 47 wt. % in the 250°C+ residue).
Relatively high aromatic hydrocarbons content (approx. 43 wt. 5% in the 250°C+-residue).
Low resin content (approx. 8 wt. 8)in the 2M°C+ residue.
Low asphaltene content (0.2 wt. %) in the fresh crude oil.
B. Physical properties with increased weathering
Relatively high evaporative loss (25 - 35% evaporated after 1 day at sea, and 35-45 after 5 days).
The fresh crude has a very high pour point even compared to other paraffinic crudes like e.g.
Veslefrikk and Statfjord. Due to weathering the pour point will increase and e.g. the spreading of the
oil at sea, the effectiveness of mechanical recovery and the effectiveness of dispersants use will be
reduced.
Low density (0.836 kgA) for the fresh crude due to high content of volatiles and saturated components.
C.
Water-in41 emnlsiation properties
Very rapid water uptake, similar to other paraffinic crudes like e.g. Veslefrikk.
High maximum water uptake (approx. 70%). This w/o-emulsion has a volume about 2-3 times that of
the oil volume at the surface.
Low initial emulsion ?ability (within approx. 24 hours) when the oil is spilt at sea, but the stability
increases with increasing evaporation degree.
The wh-emulsions recovered by mechanical recovery systems are easily broken by demulsifier
(Alcopol 0 60%).
D.
Effectiveness of dispersant treatment
Fmy has a relatively high chemical dispersability with the dispersants tested (Corexit 9500 and Dasic
NS).
"Time window" for offshore dispersant treatment similar to other paraEinic crudes Iike e.g. Veslefrikk
and Statfjord. (e.g at 5 mls wind in the summer use of dispersant is expected the be an effective
combat action at least until the oil has weathered for approx. 12 hours). However, at winter conditions
the high pour point may be the limiting factor for effective dispersability of the Frey crude.
The upper viscosity limit for dispersant treatment is ca. 6000 cP (shear rate
10 S-').
Relatively high degree of natural dispersion (approx. 20 and 60 % dispersed after 24 hours at 10 and
15 mls wind, respectively).
E.
Mechanical recovery
The w/o-emulsion reaches a viscosity of 1000 cP suitable for enhanced mechanical recovery after
about 1 hour in I5 m/s wind and after 3 hours in 5 rnls wind,
SUMMARY OF THE WEATHERING PROPERTIES OF LILLEFRIGG
CONDENSATE AT SEA
7.
These conclusion are based on a reduced laboratory study the laboratory based on the 2W°C+residue and on the
modelling predictions from Section 5. Generally are the weathering values given for a temperature of 13OC and 5
d s wind.
A.
Chemtcal properties
LilleFrigg is a relatively heavy condensate with a larger content of heavier components than other
North Sea condenstates.
a
Compared to the Frgy crude is the condensate relatively light (0.785 kgA) with a low viscosity (2 cP at
shear 100 S-'.
a
Both the vax and asphaltene content is slightly lower than the Fby crude.
B. Physical properties with increased weatbering
The high amount of heavy components gives the LilleFrigg condensate a different evaporative loss
than o h r North Sea condensates. Afier 6 hours at sea is almost 90 8 of the two Nort Sea
condensates Sleipner and Midgard evaporated while only 35 % has evaporated from the LilleFrigg
condensate.
C Water-in-oil emulsification properties
a
a
Rapid water uptake, similar to other paraffinic petroleum products like e.g. the Frgy and Veslefrikk
crudes
High maximum water uptake (approx. 70%), but forms very unstable emulsion with low viscosity and
a foamy appearance. The emulsions formed breakes completely during settling or tktment with
demulsifier.
m
-1
*.2
'
k
D.
Y
Effectiveness of dispersant treatment
a
a
a
a
a
D
E.
Due to the low viscosity on the emulsion formed has the LilleFrigg condensate a very high natural
dispersability.
The high degree of natural dispersion tagether with evaporative loss could remove the oil slick Rom
the sea surface within approximate 12 hours at 10 mls wind.
Dispersants should only be used under low sea states when the natural dispersion is low.
This condensate has a very high chemical dispersability with the dispersants tested (Corexit 9500).
"Time window" for offshore dispersant treatment will be very long (several days) due to low viscosity
and stability of the emulsion formed.
Natural dispersion may, under winter conditions, be reduced due to the relatively high pour point of
the condensate.
Mechanical recovery
a
Due to removal of the oil spill from the sea surface by evaporative loss and natural dispersion is
mechanical recovery operations expected to have limited value on this condensate.
a
At low sea states, where the natural dispersion rate is low, will the condensate form emulsions with
very low viscosities (1000 cP after 3-5 days). Mechanical recovery equipment will have a reduced
effectiveness on this low viscosity emulsion due to high leakage from the booms.
8.
SUMMARY OF THE WEATHERING PROPERTIES OF THE FR0Y
LILLEFRIGG BLEND (7525) AT SEA
These conclusion are based on a reduced laboratory study on the 200"C+ residue of this blend and on the
modelling predictions from Section 5. Generally are the weathering values given for a temperature of 13°C and 5
m/s wind. Since the Fray crude makes the majority of this blend, and the LilleFrigg condensate have a similar
content of wax and asphaltene, it shows weathering properties rather similar to the pure Fray crude.
A.
Chemical properties
The blend shows a behaviour like paraftinic crudes with a very high wax content (6.7 wt.% in 200°C+
residue).
Relatively low asphaltene content (0.27 wt. %) in the 2WC+ residue.
B. Physical properties with increased weathering
Relatively high evaporative loss (25 - 35% evaporated after 1 day at sea, and 30-45 after 5 days).
The blend has a very high pour point even compared to other paraffinic crudes like e.g. Veslefrikk and
Statfjord. Due to weathering the pour point will increase e.g. the effectiveness of mechanical recovery
and of dispersants use will be reduced.
Low density (0.823 k@l) for the &sh blend due to high content of volatiles and saturated components.
Very rapid water uptake, similar to other paraffinic crudes like e.g. Frgy and Veslefiikk.
High maximum water uptake (approx. 7M). This wlo-emulsion has a volume about 2-3 times that of
the oil volume at the surface.
Low initial emulsion stability (within approx. 24 hours) when the oil is spilt at sea, but the stability
increases with increasing evaporation degree.
The wlo-emulsions recovered by mechanical recovery systems are easily broken by demulsifier
(Alcopol 0 60%).
D.
Effectiveness of dispersant treatment
?his blend has a relatively high chemical dispersability with the dispersants tested (Corexit 9500).
"Time window" for offshore dispersant treatment similar to o h r paraffinic crudes like e.g. Fmy
crude, Veslefrikk and StatfJord. (0.5 to 3 days depending upon the weather conditions). However, at
winter conditions the high pour point may be the limiting factor for effective dispersability of this
blend after 1 to 4 hours at sea.
The upper viscosity limit for dispersant treatment is expected to be like the Fray crude; ca. 6000 cP
(shear rate 10s-1).
Relatively high degree of natural dispersion (approx. 35 and 65 % dispersed after 24 hours at 10 an 15
m/s wind respectively).
E.
Mechanical recovery
The wlo-emulsion reaches a viscosity of 1000 cP suitable for enhanced mechanical recovery efficiency
after about 3 hour in 15 m/s wind and after 6 hours in 5 m/s wind.
9.
REFERENCES
AAMO O.M., REED M,, DALING P.S., JOHANSEN O., 1993: A laboratory-based weathering
model: PC version for coupling to transport models. Proceedings of the 16. AMOP seminar,
Environment Canada.
BOCARD, C., CASTAING, G., GATELLIER, C. 1984: Chemical oil dispersion in trials at sea in
laboratory tests: the key role of dilution processes. In: Oil Spill Chemical Dispersants:
Research, Experience and Recommendations, STP 840, Tom E. Allen, Ed., American Society
for Testing and Materials, Philadelphia, pp. 125- 142.
BRANDVIK P.J., DALING P.S. and AARESKJOLD K., 1990: "Chemical dispersability testing
of fresh and weathered oils - an extended study with eight oil types" IKU-report no.
02.0786112190.
DALING, P.S. and ALMAS, I.K., 1988: Description of laboratory methods in part 1 of the
DIWO-project. IKU-report no. 02.078612188. IKU, Trondheim, Norway.
DALING, P.S., BRANDVIK, P.J., MACKAY, D., JOHANSEN, 0. 1990: Characterisation of
crude oils for environmental purposes. Paper at the 13th AMOP seminar, Edmonton, Canada,
1990. DIWO-report no. 8. IKU Report 02.0786.00108190. 22 p. Open.
DALING, P.S., BRANDVIK, P.J., MACKAY, D., JOHANSEN, 0. 1990: Characterisation of
crude oils for environmental purposes. Paper at the 13th AMOP seminar, Edmonton, Canada,
1990. DIWO-report no. 8. IKU Report 02.0786.00108190. 22 p. Open.
ENVIRONMENTAL PROTECTION AGENCY (EPA), 1982: Manual of practice - Chemical
Agents in Oil Spill Controll, EPA-report no. 60018-82-010, Washington DC, 1982.
HOKSTAD, J.N., DALING, P:S, LEWIS, A and KRISTIANSEN, T.S., 1993: Methodology For
Testing Wlo-emulsions And Demulsifiers. Description Of Laboratory Procedures.
ITOPF, 1986: Fate of Marine Oil Spills. Technical information paper no. 11186. The
International Tankers Owners Pollution Federation Ltd., London, England.
JOHANSEN, 0. 1991: Numerical modelling of physical properties of weathered North Sea crude
oils. DIWO-report no. 15. IKU-report 02.0786.00115191. Open.
MACKAY, D., BUIST, I., MASCARENHAS, R., PATERSON, S., 1980: "Oil Spill Processes
and Models". Report EE-8, Environment Canada, Ottawa, Ontario.
MACKAY, D., SZETO, F. 1980: Effectiveness of oil spill dispersants - development of a
laboratory method and results for selected commercial products. Institute of Environmental
Studies, University of Toronto, Publ. no. EE-16.
MACKAY, D. and ZAGORSKY, W., 1982: "Studies of W10 Emulsions". Report EE-34:
Environment Canada, Ottawa, Ontario.
NORDVIK, A.B., DALING, P., ENGELHARDT, F.R. 1992: Problems in the interpretation of
spill response technology studies. In: Proceedings of the 15 AMOP Technical Seminar, June
10- 12, Edmonton, Alberta, Canada, pp.211-217.
SINGSAAS, I., DALING, P.S., and JENSEN, H. 1993: Meso-scale laboratory weathering of
oils. IKU Report 22.2042.00104193,IKU, Trondheim, Norway, 81 p.
SPEIGHT, J.G. 1980: The chemistry and technology of petroleum. Corporate Research
Laboratories. Exxon Research and Engineering Company Linden, New Jersey, 8 1-88.
APPENDIX A
Physico-chemical resurlts
a
U
I
. m.
4
4 4
. .
0 W
4
W
. .
q m
P N
N
I m m
1
4 - m m o
. . . . .
I
I
1
mwr-mm
1
l
I
-+
U
X
c.
+ + + .
I:UUU.C
N m 0 o o
.
Q w o o o
!+memo
a
hh-INNN
W
El
4
0
U
!
I
1
l
I
I
I
I
m
-
I
I
1
1
I
1
I
1
I
0
m
W
I
I
1
1
l 1
W
A
a
H
I
1
I
I
I
I
I
I
I
V1
V1
N I
U
p.
V 1 l l l l l
V1
W
A
a
m
a
0
1
rW
I
l
I
I
1
I
1
I
I 1
I
. . . . .
I
l
. .
O 4
mm
4
0 P
..
. .
l a m
m m
wr-
I r - m
l
4 4 r l N N
O N O - w r - m 4 4
I
I
l
-+
I
-+
U
m
W
N
0
0
U
..
W
X
I:
a
+ + + .
0 0
.
3 L - m 0 m 0
O h r l N N N
; l m o o o
;
l L00
h C U U U C
Y
4
V)
U
a
3
n
0
0
m
N
0
X
I
:
a
I4
W
A
X
0
+ + .
ahrlNNN
.
A
I X U U V C
r Go 0 0
Q w o o o
a !4momo
0
C
+ + .
.
h h 4 N N N
N G o 0 0
~ C ! O O O
g L - m 0 m 0
I.CUUUL2
a
W
A
A
H
A
H
0
0
0
I
I
1
I
I
0
I
I
1
U
0
0
m
X
0
a
C
H
+ + .
a
a
.
WCUUUX
A m 0 0 0
A m o o 0
H ! 4 m o m o
A L 4 N N N
....
4mWW
mmwrI
..
r-m
I l l r l 4
4 4
I 1 1 4 m
S I W T E F PROUP
@ omo
m m
W
U C
m U
EoO
0
U
m
H W
nli m
h
.am
U
K 2 W
CJu E
b
2 0
m U
U-I a
m m m
m
O V U
m
.d
U
u m 7 ,
u 4
X C 0
n
U
U
.d
m
Par U
c c
0 0
U
L1
.A
u
K
0
m m c
QJ
m L1
U K
.r(
W
.d d
m
a
K C
x
U C U
Z1m m
0 4 5
TaOle A2: I'llysicnl r~rrriablesfor 6 North Sea oils.
Oil
tn?e
Boiling tsmp.
liquid (OC)
FR0Y CRUDE:
Fresh
LILLEFRIGG CONDENSATE:
Fresh
150°C+
2OO0C+
250°C+
2 0 . h. ph.ox ( 2 5 0 ° C + )
255
FR0Y-LILLEFRIGG BLEND (50:50):
Fresh
PR0Y-LILLEFRIGG BLEND (75:25):
Fresh
15O0C+
2oo0c+
250°C+
2 0 . h. ph.ox ( 2 5 0 ° C + )
251
-
GULLFAKS CRUDE:
Fresh
150°C+
2OO0C+
250°C+
2 0 . h. ph.ox ( 2 5 0 ° C + )
190
245
295
-
Vol.%
Topped
Wt.%
Residue
~snsity
(15.S°C)
Pour
point (OC)
1)
Viscosity
(cP, 13OC)
.
Interf
tens. (mN/m)
Flash p.
(OC)
@ OErl
SINTEF PROUP
0.82
Fersk
1WC+
2OO0C+
Ph. ox.
250°C+
Oil residue
Figure A I
Density of the fresh crudes and residues. Temperature 15.5"C.
high virovty due
to pour point problems
500
400
..."
300
200
----Q
*---------
100
Fersk
150"C+
2WC+
250"C+
Ph. ox.
Oil residue
Figure A2
Viscosity measwed at shear rate 100 ssl of the fresh crltdes arid the \ ~ j o t e r f r ~ e
residues.
OEY
SINTEF OROUP
-
Fmy
LilleFrigg
-.o-Fr~y-LilleFngg5050
Fmy-LilleFfigg7525
- - 0 - - Gullfaks
Veslefrikk
Fersk
15O0C+
2WC+
250°C+
'
Ph. ox.
Oil residue
Figure A3
Pour point of the fresh crudes and the residues.
1
1
Fersk
I
150aC+
I
2WC+
Oil residue
Figure A4
Flash point of the fresh crudes and the residites.
l
25O0C+
I
Ph. ox.
ll
-
LilleFrigg
-.*-. FmyCilleFrigg 50:50
-..m. .-Fmy-LilleFrigg75:25
--0--
Fersk
150°C+
2WC+
250°C+
Gullfaks
Ph. ox.
Oil residue
War content of the fresh crudes and the residues.
Figure A5
0.0
-I
-.+-.
Fray-LilleFrigg 50:50
--0--
Gullfaks
,
Fersk
150°C+
I
,
I
2WC+
250°C+
Ph. ox.
Oil residue
Figrcre A6
"I-lard" osplialtet~escotlterlr of the fresh crlcdes and the residues.
.
a
.I.~~'-,JIa
Aromallcs
I I
t
250°C+
rs
-
l
20 h. ph. ox.
-
S
i
Polar A
(Res~ns)
-
i
-
J
a ' '
!
~
~
Figure A7
~
1
'
~
~
"
'
!
~
~
~
'
~
~
~
~
,.*c-
Composition
of
the
Fr0y
crude
analyzed
a)
25O0C+-residue (topped)
Photo-oxidised oil (20 hours, 250°C+j.
bj
by
latroscan-TLC/FID.
'
~
~
'
~
Fray crude
1 1 1 1 I I 11;
.F?
Time (n1nure.l
Time (mlnuresl
I441513510-fray.3. I
800
Fray 1504
700:
Tine
lminucesl
1441513510-froy.5. I
700
Fray 250+
600-
Time
(minutes)
1441513510-froy.4, I
700-
Fray 2004
60C-
Time
Figrire A8
lmlnutesl
Gas c/rrotnatogrotns of Froj crlide oil and residries. The rl-CI7, pristatle (Pr.) 11-Cl8
axd phjtntz (I'll.) area of the fr-esh crrcde is e.rpat~ded(UChl t ~ ~ c a t Utlseparated,
ls
Cot~rplexhlatcrinl)
Ilrn
SINTCF OROUP
APPENDIX B
Emulsification (water uptake and stability)
and demulsification results
.-S I N T I C QROUP
Definitions of symbols concerning the emulsification studies:
a)
Formation and properties of wlo-emulsions
tl12Expresses the relative rate of an oil's water-in-oil emulsification ability, i.e. the time
needed for picking up half of the maximum water content (in vol.%).
Volumetric water to oil ratio in the emulsion
WOR
WORmax Maximum volumetric water to oil ratio in the emulsion measured after a rotating time of 24
hours
Stability of wlo-emulsions:
An emulsion is defined to be totally stable if no water is separated out during a 24 hour
settling period (no dehydration). T h e stability is thus expressed through the volumetric
dehydration (D24h, see definitions below) of the emulsion.
b)
Breaking of wlo-emulsions by the use of demulsifiers:
Volumetric water to oil ratio in the emulsion
WOR
WORref Volumetric water to oil ratio in the emulsion after 24 hours rotation
WOR24h Water to oil ratio in the emulsion after 24 hours rotation + 24 hours settling
-
D=
- W0R24h
1
D
Fractional dehydration of emulsion.
D24h
D = 1 means a totally unstable, or broken, emulsion
D = 0 means a totally stable emulsion
Dehydration obtained after treatment with emulsion breaker and a 24 hour settling period
% E M = % water in the emulsion after 24 hours mixing.
Relative rate of water uptake: T h e experimental data from the water uptake of the oils is
adapted to an exponential function (Mackay et al., 1980). This function is used to calculate a halflife time (tll2-value) for the maximum water uptake of the oil, i.e. the time needed for taking up
half of the maximum water content. This half-life time is further used as a parameter measuring the
relative rate of water uptake for the different residues.
Maximum water uptake: The maximum water volume that can be incorporated into an emulsion
made with the oil. It is measured after rotating a mixture of oil and water in the specified apparatus
at 3 0 rpm for 24 hours.
Dehydration: T h e dehydration of an w/o-emulsion is defined as the proportion of water that is
separated out of the emulsion after 24 hours settling, relative to the initial water volume (before
settling).
The efficiency of the wlo-emulsion breaker: This is measured from the dehydration of an wloemulsion treated with emulsion breaker in comparison to an untreated w/o-emulsion. T h e ratio of
w/o-emulsion breaker to parent oil is 2000 ppm.