Weathering, Emulsification and Chemical Dispersibility of ......Weathering, Emulsification, and Chemical Dispersibility of Mississippi Canyon 252 Crude Oil: Field and Laboratory Studies

2011 INTERNATIONAL OIL SPILL CONFERENCE

1 2011-247

Weathering, Emulsification, and Chemical Dispersibility of Mississippi Canyon 252

Crude Oil: Field and Laboratory Studies

February 10, 2011

Randy Belore, [email protected],

Ken Trudel, [email protected],

Jake Morrison, [email protected],

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

mailto:[email protected]




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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)


6 11/07/2010

16:40

na na na na na

7 11/07/2010

17:10

31.4 3 to 5 7850

(5120)


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)


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,



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



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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



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Figure 6. Progression of Emulsion During Mission #3. (left photos show surface oil appearance,



Sample ID 17-3. Red-Black Emulsion. 21 Hours after First Sample

Morning July 19


Sample ID 17-5. Red-Black Emulsion. 32 Hours after First

Sample

Morning July 19


Sample ID 17-6. Brown-Red Emulsion. 46 Hours after First Sample

Morning July 19



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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.


19 2011-247

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.

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Weathering, Emulsification and Chemical Dispersibility of ......Weathering, Emulsification, and Chemical Dispersibility of Mississippi Canyon 252 Crude Oil: Field and Laboratory Studies