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2011 INTERNATIONAL OIL SPILL CONFERENCE
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Weathering, Emulsification, and Chemical Dispersibility of Mississippi Canyon 252
Crude Oil: Field and Laboratory Studies
February 10, 2011
Randy Belore, randy@slross.com,
Ken Trudel, ken@slross.com,
Jake Morrison, jake@slross.com,
SL Ross Environmental Research Ltd.
200-717 Belfast Rd.
Ottawa, ON, Canada, K1G 0Z4
ABSTRACT
Field observations at the Mississippi Canyon 252 spill suggested that the MC252
crude oil, though very light and non-viscous when fresh, formed viscous emulsion upon
weathering. The weathering and emulsification rates of this oil were critical in
determining a) the fate and impact of the spill and b) the potential effectiveness of oil
spill countermeasures (e.g, chemical dispersants). In order to understand these processes
for MC252 oil the following studies were completed.
MC252 crude oil, collected from the Discoverer Enterprise marine riser collection
system on May 22 was weathered in the laboratory under standard conditions. Changes in
spill-related oil properties of this oil and its propensity to form emulsion were measured
at various stages during weathering.
In order to assess the potential effectiveness of oil dispersants on MC252 emulsion, 15
separate patches of MC252 oil and emulsion were sampled near the spill site from July
10 to 19, and their properties were measured. Physical properties (oil temperature,
viscosity, slick thickness, water content) of the emulsions were measured; their chemical
dispersibility was determined using a simple field test; and the visual appearance of the
surface slicks were documented photographically. The emulsions sampled showed a wide
range of properties from relatively fresh, brown/black non-viscous oil to orange/beige,
highly viscous, “peanut butter” emulsion. A number of these emulsion patches were
tracked and sampled over periods of up to 48 hours, in order to follow changes in
emulsion properties over time. This was made possible by marking the slicks with
Metocean iSphere Oil Spill Tracking Buoys.
The results of these studies are presented and the implications for understanding the fate
of spilled MC252 oil and the potential effectiveness of dispersants on emulsions are
discussed.
INTRODUCTION
The results of the laboratory analysis of fresh MC252 crude oil and a field
sampling and analysis program are reported in this paper. The laboratory analysis
completed is a standard procedure that SL Ross has completed on numerous crude oils to
assist in understanding the fate and behavior of oils when released in a marine
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environment. The objective of the field program was to gather additional information on
the various states of emulsified MC252 oil and to track the progression of the
emulsification of the oil by sampling and analyzing patches of oil over periods of up to
three days.
Three separate missions were undertaken during the field program. The first
focused on finding and characterizing as many different types MC252 oils and emulsions
as possible. This effort was completed between July 10 and 12. The second mission
tracked and measured the properties of two patches of emulsion. One patch was sampled
from afternoon through the evening of July 14 but could not be found the following
morning and was presumed to have naturally diffused and dispersed from the surface.
The second patch was monitored for 11.5 hours between 8:30 and 19:00 hrs on July 15.
In the third mission a patch of emulsion was monitored over a period of about 48 hours
from 10:45 am on July 17 to 9:00 am on July 19.
In all of the missions the emulsions were characterized by measuring their
viscosities at ambient temperature, their amenability to chemical dispersion, their water
content and by photographing the water drops in the emulsions.
METHODS
MC 252 Oil Laboratory Weathering and Analysis
Oil collected from the Discoverer Enterprise marine riser on May 22, 2010 was
subjected to a standard artificial weathering and analysis procedure conducted at SL
Ross. In this procedure the oil is divided into three aliquots. Two aliquots are weathered
in a wind tunnel: one for two days and one for two weeks. Depending on the conditions at
a spill site, this is typically equivalent to a few hours and a few days at sea. The fresh oil
is subjected to a modified ASTM distillation to obtain two oil-specific constants for
evaporation prediction purposes. The distillation information is used in conjunction with
the wind tunnel data to predict weathering rates for oil spills at sea. The fresh and
evaporated oils are subjected to the analyses outlined in Table 1. Test temperatures are
chosen to represent typical values for the region for those tests that are temperature-
sensitive, such as density and viscosity. In this application properties were measured at
15 and 35°C to bracket the environmental conditions that could be encountered in the
Gulf of Mexico.
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Table 1: Test procedures for oil analysis
Property Test Temperature(s) Equipment Procedure
Evaporation Ambient Wind Tunnel
Distillation Apparatus
ASTM D86
Density 15 and 35 °C Anton Paar Densitometer ASTM D4052
Viscosity 15 and 35 °C Brookfield DV III+ Digital
Rheometer c/w Cone and Plate Brookfield M/98
211
Interfacial Tension Room temperature CSC DuNouy Ring Tensiometer
ASTM D971
Pour Point N/A ASTM Test Jars and Thermometers
ASTM D97
Flash Point N/A Pensky-Martens Closed Cup Flash
Tester
ASTM D93
Emulsification
Tendency/Stability 15 and 35 °C
Rotating Flask Apparatus
(Mackay and
Zagorski 1982,
Hokstad and Daling
1993)
Field Program Test Methods
Surface Oil Sampling
Oil was taken from the surface using a small 1 gallon plastic bucket as a skimmer
attached to an extendable painter‟s pole. The oil and water collected was immediately
poured into a large-mouthed separatory funnel to remove any collected water. The oil
was transferred to the glass collection jars directly from the separatory funnel. For thin
slicks several dips and decants were necessary to collect an adequate sample volume.
Emulsion Viscosity
Emulsion viscosity was measured in the field using a Brookfield LVDV-E
viscometer operating at a number of spindle rotation speeds, from 1 to 100 rpm.
Emulsions were measured immediately after sampling at the temperature at which they
were collected. Viscosities were determined using the “infinite sea” approach;
measurements were made in a vessel with a very large diameter. The emulsions were also
transported to the laboratory where their viscosity were measured using a Brookfield
DVIII cone and plate viscometer operating at the temperature at which the emulsion was
collected. All viscosities have been reported at ambient temperature.
Oil Thickness
The thicknesses of the oil and emulsion patches that were sampled were estimated
visually. This was assisted by placing a 10cm x 10cm piece of sorbent pad tethered to a
cord into the oil and then removing it to reveal the nature of the surface oiling. The
amount of oil absorbed to the pad and/or the water surface exposed when the sorbent was
removed aided in visually determining the thickness of the oil patch.
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Oil Density
The oil densities were measured using an Anton Paar DMA35 portable density
meter. Emulsions were broken using heat by placing them in the sun for an extended
period and the parent oil densities were then measured.
Emulsion Water Content
The water contents of the emulsions were determined by breaking the emulsions
and measuring the resulting water and oil heights in the broken samples.
Emulsion Water Drop Size Microphotography
A small dab of each emulsion was smeared onto a microscope slide and
photographed through a microscope. The eyepiece of the microscope was fitted with an
optical scale that was visible in all photographs. One division on the scale imprinted on
each photograph corresponds to 9.8 microns. The resulting emulsion photographs provide
a qualitative record of the state of each emulsion for comparison. The relative number of
water drops, overall quantity of water, the relative sizes of water drops and how tightly
they are packed can be visually estimated from the microphotographs.
Dispersibility Testing
Dispersibility of emulsions was assessed using a simple comparative field test
(Figure 1). Approximately 500 ml of clean seawater was placed in each of two, one-litre,
wide-mouth clear glass bottles. Twenty ml of test oil/emulsion was added to each. One
ml of dispersant, Corexit 9500, was then added, drop-wise onto the oil in one of the
bottles using a 1 ml syringe and was allowed to stand for one minute. The contents of the
bottles were then mixed by inverting the two bottles, simultaneously five times at a rate
of one inversion per second and were then allowed to stand for one minute. Dispersion
effectiveness was then evaluated visually and was graded as highly dispersible,
dispersible or undispersible. All testing was completed at ambient sea temperature of
approximately 31 degrees C.
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Observation of Emulsion Sheening in Clean Water
One potential mechanism for the loss of thick oil and emulsion from the water‟s
surface is the bleeding of oil from the thick patch into a thin oil sheen adjacent to the
thick oil and the subsequent evaporation and dispersion of the oil from the sheen. The
thin sheen is much more easily evaporated and dispersed than the thick emulsion slicks or
pieces. If the „sheening‟ process occurs then there is an accelerated loss of oil from the
water‟s surface. In low energy situations, oil sheens can cover a broad area around the
thick oil or emulsion patches and will not be dispersed very readily due to the low sea
states. Once sea states increase the sheen will disperse and then be replaced by more
sheen from the thick patches. This process eventually erodes away the thick patches of
emulsion. To test whether this process would likely occur with the emulsified MC252
oils small samples of the emulsions (about 1 to 3 ml each) were observed on clean water
away from the immediate vicinity of the spill site. The behavior of the emulsion bits was
observed and video taped. Similar tests were conducted where some of the heavier
emulsion bits were treated with Corexit 9500 dispersant, placed on the clean water
surface, observed and video taped.
a . b
c d
.
Figure 1 . Field dispersant effectiveness test.
a. Water and emulsion added to two glass jars.
b. Dispersant added to the emulsion slick dropwise.
c. Two jars inverted slowly five times and allowed to sett le .
d. Effectiveness assessed after one minute of settling.
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Oil Slick Tracking
Surface oil slicks were tracked visually during the day and using iSphere satellite
tracked buoys manufactured by MetOcean (see Figure 2) over night. The iSphere buoys
were configured to provide their positions by longitude/latitude every 15 minutes. This
allowed them to be found in the morning after tracking the oil through the night when
visual monitoring of the slicks was not possible.
Figure 2. iSphere Surface Oil Tracking Buoy
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RESULTS
Laboratory Weathering and Oil Analysis
The results of the laboratory weathering and property analysis are summarized in
Table 2. The key findings of this analysis with respect to oil spill behavior and spill
response are summarized below:
1. The fresh MC252 oil is very light and non-viscous (0.825 g/cm3, API °37.2 and
1.4 cP at 35 °C).
2. Even when evaporated to a volumetric loss of 45% the oil remains relatively non-
viscous (23 cP at 35 °C)
3. The oil was not susceptible to emulsion formation with up to 45% loss of its light
ends. (after two weeks in the wind tunnel).
4. The oil formed stable emulsions only after 55%1 loss by volume.
5. The oil‟s pour point is quite low (6 °C) even when extensively weathered.
1Since emulsified MC252 was common during this spill event additional weathering past the standard
2 week maximum was added to the test procedure to identify the evaporative loss at which
emulsification could be expected to occur. At approximately 55% volumetric loss the MC252 oil was
shown to form emulsions in the laboratory test. Photo oxidation in the actual spill setting may result in
emulsification occurring at somewhat less volume loss.
Comparison of Lab Analysis to „Fresh Oil‟ Field Sample Properties
A sample of un-emulsified MC252 oil that was believed to be relatively fresh
(based on visual inspection) was taken from the water surface by the study team at a
location 28 48.072N 088 32.924W in a patch of black oil with some trace of emulsion on
May 17, 2010. This location was approximately 10 miles from the well site. This oil had
a density of 915 kg/m3 at 26.5 °C. This is a similar density to the most heavily evaporated
oil from the wind tunnel tests (899 kg/m3 at 35 °C). The increase in density of the field
sample will have been due to the weathering of the oil both as it rose through the water
column and once it reached the surface. Based on the wind-tunnel weathering and oil
density measurements, the surface sample that was considered “relatively fresh” would
have lost about 55% of its original volume by the time it was sampled. The lack of
significant emulsification of this oil sample (as determined through microscopic
examination) is consistent with the laboratory weathering predictions that emulsification
of the oil is unlikely to occur until a significant loss of the lighter ends of the crude oil.
The history of the sampled oil is not known so its time on the surface prior to sampling
and exposure to winds and waves is unknown.
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Table 2. Oil Analysis Summary Spill-related properties BP MC252 ENT-052210-178 API ° = 37.2
Evaporation (Volume %) 0 34.50 44.66
Density (g/cm3)
15 °C 0.839 0.882 0.897
35 °C 0.825 0.868 0.883
Dynamic Viscosity (mPa.s) at approx 460 s-1
15 °C 4.1 43 85
35 °C 1.4 10 23
Kinematic Viscosity (mm2/s)
15 °C 4.8 49 95
35 °C 1.7 12 26
Interfacial Tension (dyne/cm)
Oil/ Air 23.5 26.8 30.1
Oil/ Seawater 23.3 22.6 22.5
Pour Point (°C)
<-9 6 6
Flash Point (°C)
<-8 54 100
Emulsion Formation-Tendency and Stability @ 22.5 °C
Tendency Unlikely Unlikely Unlikely
Stability Unstable Unstable Unstable
Water Content 0% 0% 0%
Emulsion Formation-Tendency and Stability @ 34 °C
Tendency Unlikely Unlikely Unlikely
Stability Unstable Unstable Unstable
Water Content 0% 0% 0%
ASTM Modified Distillation
Liquid Vapour
Evaporation Temperature Temperature
(% volume) (°C) (°C)
IBP 84 39.8
5 111.6 77.4
10 124.4 91.7
15 137 102.4
20 151.2 115.8
25 168.8 116
30 188.2 126.4
35 208 150
40 227 129.7
45 248 142.5
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Field Mission #1
The first field mission was conducted on July 10 through July12, 2010. The goal
of this trip was to find and characterize as many patches of MC252 emulsion with
varying appearance as possible. The team was also instructed to look for and document
surface anomalies that could be oil in various states of weathering or other material that
could be mistaken for oil. Table 3 below provides a brief description of the sample
locations. Table 4 provides emulsion property data collected at each site.
Table 3. Sample Location Descriptions
Sample ID Date:dd/mm/yy
Time: hr:min Description of Sample
1 10/07/2010
15:15
Surface material that looked like stringers of „tea-leaf‟ water-in-oil
emulsion. Close microscopic examination of the collected product revealed
the presence of primarily organic matter with no oil present (this confirmed
by extraction with xylene solvent).
2 10/07/2010
19:00
An anomaly that could be similar to the „dark clouds‟ that have been
reported. Water samples were taken in both the dark and light water. The
water temperatures were measured and the dark water was found to be
about a degree colder than the lighter colored water. Everyone viewing the
anomaly agreed that this was a case of clear, cold, water up welling into a
zone of turbid water
3 11/07/2010
11:00
The third stop was an investigation of small pieces of red emulsion about
3mm thick surrounded by sheen.
4 11/07/2010
15:00
Very viscous tan colored emulsion (warm peanut butter consistency). This
was an isolated single patch of emulsion about 3 m in diameter and 3 to 5
cm thick.
5 11/07/2010
16:00
Reddish-brown emulsion in ribbons 2 to 3 m wide.
6 11/07/2010
16:40
Water sample taken in a convergence zone. Large quantities of particulates
and debris in water on one side of zone, blue water on other. Mix of
seaweed and emulsion on surface along the convergence line.
7 11/07/2010
17:10
Red emulsion with swirls of black oil.
8 11/07/2010
19:00
Black, relatively fresh oil.
9 12/07/2010
08:20
Red emulsion with some black oil swirls, large patch, 20-30m diameter.
10 12/07/2010
11:15
Red emulsion.
11 12/07/2010
12:02
Black oil with some brown streaking. Very thick (1 to 2 inches), large
patch. Size of football field or greater. Oil was hot on surface was black,
but more brown underneath. Likely due to emulsion breaking on the very
hot surface layer.
12 12/07/2010
14:30
Surface (upper 1 m) water sample in a convergence zone setting with a
significant quantity of floc. Living mysids were identified in the sample
with the microscope.
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Table 4. Preliminary Data Collected During Field Mission #1
The photos in Figure 3 provide a visual summary of the major oil/emulsion types
sampled during the first mission ranging from nearly fresh oil at location 8 to the very heavily
emulsified oil sampled at location 4. The emulsion micro-photographs provide a qualitative
succession of water drop size characteristics for the progressively more viscous emulsions. With
the exception of the most viscous emulsion the oils were deemed dispersible in the field
effectiveness test.
Sample ID Date:dd/mm/yy
Time: hr:min
Oil
Temp
(C)
Thickness
(mm)
Viscosity
(cP @10s-1)
at ambient
temp.
(cone&plate)
Parent Oil
Density
(g/cc)
@27C
Water
Content
(%)
Dispersibility
with
Corexit 9500
1 10/07/2010
15:15
32 1 na na na na: organics
2 10/07/2010
19:00
31.2
32.3
na na na na na
3 11/07/2010
11:00
32.1 3
(blobs)
1680
(1550)
0.934 31 dispersible
4 11/07/2010
15:00
31.1 30 to 50 >20,000
(>1,966,000)
0.973 34 not
dispersible
5 11/07/2010
16:00
31.1 3 to 5 <18,500
(7500)
0.948 53 dispersible
6 11/07/2010
16:40
na na na na na
7 11/07/2010
17:10
31.4 3 to 5 7850
(5120)
0.939 60 dispersible
8 11/07/2010
19:00
30.5 2 126
(72)
0.907 12 highly
dispersible
9 12/07/2010
08:20
31.3 5 to 15 1750
(7580)
0.944 40 dispersible
10 12/07/2010
11:15
32.1 2 to 3 1600
(7342)
0.939 55 highly
dispersible
11 12/07/2010
12:02
48.1 20 to 50 160
(760)
0.937 39 highly
dispersible
12 12/07/2010
14:30
30.2 na na na na na
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Figure 3. Progression of MC252 Emulsions (left photos show surface oil appearance, centre
photos show microphotographs of the oil: each scale division is 9.8 microns, right photos show
field dispersibility test results)
Sample ID 8. Black Fresh Oil (12% water content, 126 cP) Highly Dispersible
Sample ID 9. Red Emulsion with Black Swirls (40% water content, 1750 cP) Highly
Dispersible
Sample ID 7. Red Emulsion with Black Swirls (60% water content, 7850 cP)
Dispersible
Sample ID 4. Tan Emulsion (40% Water Content,
>20,000 cP) Not Dispersible
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Field Mission #2
The efforts in mission #2 were directed towards tracking patches of emulsified MC252
oil and monitoring their property change over time. The patch of emulsion found at location 14
was sampled in early afternoon and evening and then tracked overnight, but could not be found
in the vicinity of the tracking buoys the next morning so it was assumed to have dispersed or
diffused to an undetectable level. Another sizeable slick of relatively fresh oil/emulsion was
found with the help of the spotter aircraft at location 16 and this was tracked from late morning
until the evening on July 15th. Table 5 provides a brief description of the oil encountered at each
sample location. Table 6 provides data collected at each site.
Table 5. Descriptions of Oil / Emulsion at Each Sample Location
Sample
ID
Date:dd/mm/yy
Time: hr:min Description of Sample
Location 14 was the first oil that was sampled over an extended time frame.
14 14/07/2010
13:00 to 14:20
Red and black oil. Fairly fresh un-emulsified oil as seen in
the emulsion microphotographs. Thin and patchy oil
difficult to sample.
14-1 14/07/2010
18:00
Oil starting to take on a less red and more red-brown in the
thicker areas. Oil streamers were still visible and buoys
seemed to be tracking between two major streamer 'lines'.
15/07/2010
07:00 to 08:30
Could not find oil the following day in the vicinity of the
tracking buoys. The oil appeared to disperse / diffuse to
undetectable overnight.
Location 16 was the second oil patch that was sampled over an extended time frame.
16 15/07/2010
11:25
Brown oil with black streaks, 2 to 3mm thick. A streamer
about 3 to 5 m wide and a few hundred m long.
16-1 15/07/2010
15:45
2nd sampling of oil streamers being tracked. Oil appearance
similar to sample location 16.
16-2 15/07/2010
19:00
Still some black streaks but mostly red/orange emulsion at
the time of this last sampling.
The photos in Figures 4 and 5 provide visual summaries of the progression of the
emulsions over time for the two patches that were tracked over the extended periods. There was
a definite increase in viscosity and water content over the fours hours that the oil was tracked at
location 14. The starting emulsion in this case had a relatively low water content and viscosity so
was likely in its early stages of emulsification when first sampled.
There was a slight increase in the parent oil density and viscosity of the emulsion at
location 16 over the full 8-hour tracking period.
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Table 6. Data Collected During Field Mission #2
Sample
ID
Date:dd/mm/yy
Time: hr:min
Temp.
(C)
Thickness
(mm)
Viscosity (cP @~10s-1)
at ambient
temp.
(cone&plate)
Parent
Oil
Density
(g/cc)
@27C
Water
Content
(%)
Dispersibility
with
Corexit 9500
14 14/7/2010
14:00
32.8 0.5 to 1 130
(950)
0.924 17 highly
14-1 14/7/2010
18:00
33.2 1 to 2 <17,000
(6900)
0.947 44 highly
16 15/7/2010
11:25
30.8 1 to 2 3100
(2400)
0.923 64 highly
16-1 15/7/2010
15:45
32.2 1 to 2 2400
(2300)
0.923 57 highly
16-2 15/7/2010
19:00
31.7 1 to 2 4300
(4560)
0.934 44 highly
Figure 4. Progression of Emulsion at Location 14 (left photos show surface oil appearance,
centre photos show microphotographs of the oil: each scale division is 9.8 microns, right photos
show field dispersibility test results)
Sample ID 14. Red and Black Oil (17% Water Content, 130 cP) Highly Dispersible
Sample ID 14-1. Red and Red-Brown Emulsion: 4 Hours Later
(44% Water Content, >17,000 cP) Highly Dispersible
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Figure 5. Progression of Emulsion at Location 16 (left photos show surface oil appearance,
centre photos show microphotographs of the oil: each scale division is 9.8 microns, right photos
show field dispersibility test results)
Sample ID 16. Red Emulsion Streamers (Water Content 64%, 3100 cP) Highly Dispersible
Sample ID 16-1. Red Emulsion Streamers: 4.5 Hours from First Sample
(Water Content 57%, 2400 cP) Highly Dispersible
Sample ID 16-2. Red-Orange Emulsion Streamers: 8 Hours from First
Sample
(Water Content 44%, 4300 cP) Highly Dispersible
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Field Mission #3
In the third mission a patch of emulsion was identified by the spotter aircraft at N28
50.86, W88 26.91 and was tracked and sampled for approximately 48 hours from the morning of
July 17 to the morning of July 19. Table 7 below provides a brief description of the oil at the
times and locations when this oil was sampled. Table 7 provides data collected at each location.
Over the full period of monitoring this oil there was not an appreciable change in the
characteristics of the emulsion. Figure 6 provides a visual account of the emulsion characteristics
over the tracking period.
Table 7. Sample Location Descriptions
Sample
ID
Date:dd/mm/yy
Time: hr:min Description of Oil when Sample was Taken
17
17/07/2010
10:40
Red-brown emulsion with some black swirls. Oil in form of
more discrete particles in the patches have thinner average
thickness and were more red in appearance. The thicker, more
continuous slicks were more „brown with black swirls‟ in
appearance.
17-1 17/07/2010
14:40
Heavy red to red-brown emulsion patches surrounded by
sheen.
17-2 17/07/2010
19:30
Thick patch of brown emulsion with significant black oil.
17-3 18/07/2010
07:55
Separate patches of emulsion have different thicknesses and
appearance. Thinner more fragmented emulsion is red while
the thicker more continuous oil patches were brown.
17-4
18/07/2010
13:30
Oil in form of brown and red stringers. Similar thicknesses
and coloring as in sample 17-3. Oil fragments in red colored
emulsion are 10 to 25 mm in diameter herded into patches or
slicks of various sizes (few meters to several meters in
diameter).
17-5 18/07/2010
18:30
Emulsion patches were various in appearance. Ranged from
thick brown to thick brown with black and thinner red. Glassy
sea conditions.
17-6 19/07/2010
09:00
Similar appearance to sample 17-5 at the end of the previous
day. Emulsion did not changed in appearance appreciably
overnight.
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Table 8. Data Collected During Field Mission #3
Sample
ID
Date:dd/mm/yy
Time: hr:min
Temp.
(C)
Thickness
(mm)
Viscosity
(cP @~10s-1)
at ambient
temp.
(cone&plate)
Parent
Oil
Density
(g/cc)
@27C
Water
Content
(%)
Dispersibility
with
Corexit 9500
17 17/07/2010
10:45 31.7 2 to 7
7200
(7700) 0.939 51 highly
17-1 17/07/2010
14:40 32.3 3 to 7
9150
(8650) 0.942 61 dispersible
17-2 17/07/2010
19:35 30.6 5 to 10
5400
(5300) 0.939 32 highly
17-3 18/07/2010
7:55 30.8 1 to 5
6600
(6300) 0.939 43 highly
17-4 18/07/2010
13:30 33.7 5 to 10
7700
(8500) 0.948 33 dispersible
17-5 18/07/2010
18:30 31.5 1 to 10
5800
(5200) 0.938 42 highly
17-6 19/07/2010
09:00 31.2 1 to 7
6000
(6300) 0.943 36 highly
Sample ID 17. Red-Black Emulsion (Water Content 51%, 7200 cP) Highly Dispersible
Sample ID 17-2. Black oil with Brown Emulsion. 9 Hours after First
Sample
End of Daylight July 17
(Water Content 32%, 5400 cP) Highly Dispersible
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Figure 6. Progression of Emulsion During Mission #3. (left photos show surface oil appearance,
centre photos show microphotographs of the oil: each scale division is 9.8 microns, right photos
show field dispersibility test results)
Sample ID 17-3. Red-Black Emulsion. 21 Hours after First Sample
Morning July 19
(Water Content 43%, 6600 cP) Highly Dispersible
Sample ID 17-5. Red-Black Emulsion. 32 Hours after First
Sample
Morning July 19
(Water Content 42%, 5800 cP) Highly Dispersible
Sample ID 17-6. Brown-Red Emulsion. 46 Hours after First Sample
Morning July 19
(Water Content 36%, 6000 cP) Highly Dispersible
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Behavior of Emulsions on Clean Sea Water
Extensive areas of heavy oil sheens surrounded the large mats and windrows of emulsion
that were encountered. The missions were also completed in relatively calm conditions with little
or no breaking wave action. As a result the patches of emulsion appeared to be very persistent
with only minor changes in appearance over the few days that they were observed. Under
rougher sea conditions the extensive areas of sheen surrounding the emulsion patches would
likely be dispersed thus exposing the emulsion to clean water at its perimeter. Heavier seas
would also break up the emulsion into smaller pieces or bits with a larger perimeter and surface
area. To assess how smaller pieces of emulsion might behave when exposed to areas of clean
water small pieces (a few millilitres each) of four types of the MC252 emulsions were placed on
clean sea-water under calm sea conditions and light winds. The behavior of the emulsions was
observed and video taped. The less viscous emulsions (black-red, red and red-brown) all quickly
generated extensive sheens and within minutes or less were completely converted to surface oil
sheen. The thicker tan (peanut butter like) emulsion sampled at location #4 formed sheens less
vigorously and persisted for longer periods. Dispersant was added at a 1:20 DOR to the
persistent emulsion and small pieces of the treated emulsion were placed on an „oil-free‟ surface.
The emulsions formed sheen more quickly than the cases where no dispersant was applied. The
results of this exercise demonstrate a possible mechanism for the conversion of the persistent
emulsion patches to thin oil sheens and ultimately finely dispersed and evaporated oil.
CONCLUSIONS
The MC 252 oil is a light crude that can lose in excess of 55% of its volume through
evaporation or dissolution prior to it forming stable water-in-oil emulsions.
The majority of the oil and emulsion samples collected in the field had parent oil
densities that would indicate that in excess of 55% of the initial oil volume had been lost through
evaporation or dissolution prior to the sampling.
The emulsions sampled had water contents ranging from 12% (weathered and lightly
emulsified oil) up to 64%. Only two samples had water contents less than 30%.
Emulsion viscosities ranged from a few hundred to tens of thousands of cP. Most of the
red, red-black and red-brown emulsions had viscosities between 2500 and 7500 cP at ambient
temperatures.
Only one isolated small patch of tan, peanut butter like emulsions with very high
viscosity was encountered in the three, 3-day missions.
The water droplet sizes in the emulsions generally reduced in size and increased in
numbers as the oils emulsified, as would be expected.
All but the tan emulsion was dispersible in the field dispersion test.
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When placed in clean water the less viscous emulsions (black-red, red and red-brown) all
quickly generated extensive sheens and within minutes or less were completely converted to
surface oil sheen. The thicker red-tan and tan (peanut butter like) emulsions formed sheens less
vigorously and persisted for longer periods. Dispersant was added to the persistent emulsions and
small pieces of the treated oil were placed on an „oil-free” surface. Both persistent emulsions
formed sheen more quickly when treated with dispersants. This demonstrates that dispersants
may be useful in treating even the most viscous of the emulsions that were encountered under
higher sea states. The results of this exercise demonstrate a possible mechanism for the
conversion of the persistent emulsion patches to thin oil sheens and ultimately finely dispersed
and evaporated oil.
REFERENCES
Hokstad, J. and P. Daling. 1993. Methodology for Testing Water-in-Oil Emulsions and
Demulsifiers. Description of Laboratory Procedures. In Formation and Breaking of Water-in-
Oil Emulsions: Workshop Proceedings Marine Spill Response Corporation, Washington DC,
MSRC Technical Report Series 93-108, pp 239-254
Zagorski, W. and D. Mackay. 1982. Water in oil emulsions: a stability hypothesis, in
Proceedings of the 5th Arctic and Marine Oilspill Program Technical Seminar, Environment
Canada, Ottawa, ON, pp 61-74.