Luno II crude oil - properties and weathering at sea - related to oil spill response

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SINTEF Materials and Chemistry Oil Spills Research

2014-05-13

A26115- Unrestricted

Report

Luno II crude oil – properties and weathering at sea

Related to oil spill response Author(s)

Kaja Cecilie Hellstrøm Marius Johnsen

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(,)SINTEF

SINTEF Materialer og kjemi SINTEF Materials and Chemistry Address:

Postboks 4760 Sluppen N0-7465 Trondheim NORWAY

Telephone:+47 73593000 Telefax:+47 73597043 lnfo.mk@sintef.no www.sintef.no/mk Enterprise /VAT No:

NO 948007029 MVA

KEYWORDS:

Weathering of oil Dispersibility

Meso-scale experiment Emulsion Properties

Report

Luno li crude oil - properties and weathering at sea

Related to oil spill response

VERSION

1.0

AUTHOR(S)

Kaja Cecilie Hellstrøm Marius Johnsen

CUENT(S)

Lundin Norway AS

PROJECTNO.

102005636

ABSTRACT

Abstract heading

DATE

2014-05-13

CLIENT'S REF.

Geir-Olav Fjeldheim

NUMBER OF PAGES/APPENDICES:

90 lncluding Appendices

A study of the weathering properties of Luno li has been performed using both small and meso-scale laboratory testing at two temperatures, 5^°C and 13^°C. The obtained data was used as input in the SINTEF Oil Weathering Model (OWM) to predict the fate and behaviour of Luno li in a spill situation at sea. The weathering properties are discussed in relation to oil spill response; mechanical recovery and chemical dispersion.

PREPARED BY

Kaja Cecilie Hellstrøm

CHECKED BY

Kristin Rist Sørheim

APPROVED BY

Ivar Singsaas

REPORT NO.

A26115

ISBN

978-82-14-05738-6

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Document history

VERSION DATE VERSION DESCRIPTION

1.0 2014-03-11 Draft version

1.0 2014-05-11 Final version

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1 Executive summary

When weathered on the sea surface, both oil and condensates will undergo changes that affect oil spill countermeasures in various ways, as a function of time and weather conditions. This summary gives a brief overview of the main changes to Luno II crude oil when weathered on the sea surface, and compares the changes to previously studied oils.

Luno II is a medium heavy paraffinic crude oil with a density of 0.851 g/ml, a medium asphaltene content of 0.5 wt. % and a low wax content of 2.7 wt. %. High initial evaporative loss will result in a relative increase of asphaltene and wax content, if the oil is spilled at sea. This relative increase of heavy end components will alter the chemical properties of the oil. Luno II rapidly forms stable water-in-oil (w/o) emulsions with relatively high viscosities in both summer and winter conditions. Luno II is predicted to have a long lifetime at sea except in very high sea states (wind =15 m/s), where the evaporative loss and natural dispersion combined will remove the oil from the sea surface within five days based on the mass balances.

As oil is spilled on the sea surface, the temperature of the oil will be cooled to the ambient water temperature within a short period of time. The fire hazard will be at its greatest as long as the flash point of the oil is below the sea temperature. For Luno II crude oil the flash point will be above the sea temperature within one hour in low wind (2m/s) in winter temperature, and faster in summer temperature and with higher wind speeds due to faster evaporation of lightest compounds. Some vessels engaged in oil recovery operations may not be classified to carry liquids with flash point lower than 60°C. Luno II will reach this limit in low wind conditions (2 m/s) after 12 hours at winter temperature and within six hours in summer temperature.

Luno II forms stable emulsions at both summer and winter temperatures. The maximum water contents of the emulsions are generally higher at 13°C compared to 5°C; maximum water content is 56 vol. % at 5°C compared to 71 vol. % at 13°C. The crude oil exhibits rather high emulsion viscosities, and the viscosities increase considerably with increasing water content.

As Luno II rather rapidly forms highly viscous emulsion, boom leakage will only be a problem for the first 12-14 hours in very calm conditions (2 m/s wind speed), when the emulsion viscosities are below 1000 mPas. However, as Luno II forms emulsions with high viscosities (20000 mPas) e.g. after 12 hours of weathering at 10 m/s wind speed, the oil is expected to have reduced flowability towards weir skimmers. The use of "high visc." skimmers could therefore be recommended.

In general Luno II has a potential for use of chemical dispersant. The oil is expected to be easily dispersed with viscosities lower than 3000 mPas, and has reduced chemical dispersibility up to viscosities of 25000 mPas. For optimal results the dispersants should be applied as quickly as possible; in strong wind (15m/s) the emulsion reaches the viscosity limit for dispersibility within six hours. Once the oil is expected to have reduced chemical dispersibility, additional energy or a higher dispersant dosage (DOR= dosage to oil ratio) should be applied. Repeated application of dispersant may also increase the effectiveness, especially in calmer sea states. Additional energy can be provided using firefighting (Fi-Fi) systems, thrusters or MOB boats after dispersant application in order to enhance dispersant effectiveness.

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2 Introduction

New oil types (from heavy crude oil to light crude oils and condensates) are continuously coming into production worldwide. Due to large variations in different crude oils’ physical and chemical properties, their behaviour and fate may vary greatly if spilled at sea. The “Braer” accident at the Shetlands (1993) and the

“Sea Empress” accident in Wales (1996) have demonstrated how different the fate and behaviour of the oils can be when spilled on the sea surface. For that reason, having good knowledge about the expected behaviour of oil at sea in case of an accidental spill is highly valuable.

Recent dispersibility studies of the oil spilled after the Deepwater Horizon incident in the Gulf of Mexico (2010) clearly showed how dispersant application efficiency may change as the oil is weathered and emulsified on the sea surface over a longer period. This may form important support for refining operative strategies in terms of where, when and how dispersants could be effectively applied during a response operation.

According to the Norwegian Environment Agency and the Petroleum Safety Authority Norway (Ptil) regulations for petroleum activities (Aktivitetsforskriften §59), the characterization of oils with respect to their weathering properties and fate in the marine environment should be performed for all oils coming into production.

Figure 2-1: Location of Luno II oil field in the North Sea. (Sources:

http://www.lundin-petroleum.com/eng/exploration_programme.php,

http://www.npd.no/global/norsk/1-aktuelt/boretillatelser/b2013/16-4-6-s_ny.pdf)

Luno II is an oilfield located in the North Sea approximately 15 km south of Edvard Grieg and 200 km west of Stavanger. The reservoir is found in sandstone, 280 meters thick, from the Jurassic to Triassic epochs and is located at 1950 meters below sea surface.

On Lundin Norway's request, a full weathering study of Luno II crude oil at summer and winter temperature has been conducted. The study included small-scale laboratory testing and meso-scale flume tests at two temperatures, 5°C and 13°C. The obtained data were used in order to predict Luno II's fate and behaviour when spilled at sea, under different weather conditions. The results and predictions are discussed with regard to oil spill response operations.

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3 Experimental results

3.1 Small-scale laboratory testing results

The small-scale weathering results of Luno II are compared with similar data of other Norwegian oils, listed in Table 3-1. The oils are primarily selected based on their variety in properties and behaviour and in agreement with Lundin Norway.

Table 3-1: Oils compared to Luno II data in the report

Oil Previous name SINTEF ID Ref Rapportnr.

Edvard Grieg Luno 2010-0327 Sørheim, 2011 A18427

Ivar Aasen Draupne 2011-0001 Sørheim og Leirvik, 2011 A21165 Johan Sverdrup Avaldsnes 2011-0444 Sørheim, 2012 A22484

Grane 1997-0253 Strøm og Daling, 1997 STF66 F98038

Statfjord A 2000-0036 Moldestad et al., 2001 STF66 F00138 The Luno II crude oil used in this study was given SINTEF ID 2013-0580.

3.1.1 Chemical composition and physical properties

The chemical composition of Luno II and other crude oils are shown in Figure 3-1 and Figure 3-2 as GC/FID chromatograms. Appendix D shows the result of the chemical characterization of the fresh oil on GC/MS.

Gas chromatographic flame ionization detector (GC/FID) characterization

The chemical composition of Luno II, as characterized by gas chromatography (GC/FID), is shown in Figure 3-1. The same figure also present the gas chromatographic characterization of the corresponding residues (150°C+, 200°C+, and 250°C+), and verify the artificial evaporation of the oil by use of distillation (topping) in the laboratory.

The gas chromatograms show the n-alkenes as systematic narrow peaks and the peaks to the left in the chromatogram represent the components with the lowest boiling point. As can be seen in Figure 3-1, these components are gradually removed with higher distillation temperature. More complex components, such as resins and naphthenes, are not as easily separated as n-alkanes and form a broad and poorly defined bump below more pronounced peaks. The bump is often described as "Unresolved Complex Mixture", or UCM.

Heavier compounds such as asphaltenes (> nC40) are not possible to analyse with this technique.

The GC/FID characterization indicates that Luno II is a paraffinic crude oil reflecting a medium amount of wax/paraffinic compounds in the range of nC20-nC30 (Figure 3-1). Also the other crude oils in comparison, except Grane, exhibit hydrocarbon profiles with typically paraffinic features, as shown in Figure 3-2.

Gas chromatography (GC/FID) is an important tool for oil characterisation and for oil spill identification as an initial step. Common screening parameters used for identification, as well as for the degree of biodegradation, are the nC17/Pristane and nC18/Phytane ratios. These parameters for Luno II and other Norwegian oils are given in Table 3-2Error! Reference source not found..

Table 3-2: nC17/Pristane and nC18/Phytane ratios for Luno II fresh oil compared to other oils Oil nC17/Pristane nC18/Phytane

Luno II 1.0 1.8

Edvard Grieg 1.8 1.6

Ivar Aasen 2.2 2.8

Johan Sverdrup 1.8 1.9

Grane 1.3 N.C.

Statfjord A 1.7 2.3

N.C.: Not Calculated

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Figure 3-1: GC/FID chromatograms of the fresh and evaporated residues of Luno II crude oil Luno II Fresh oil

Luno II 150°C+

Luno II 200°C+

Luno II 250°C+

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Luno II (2013-0580)

Edvard Grieg (2010-0327)

Ivar Aasen (2011-0001)

Johan Sverdrup (2011-0444)

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Figure 3-2: GC/FID chromatograms for fresh residues of other relevant crude oils Asphaltene and wax content

The chemical properties of asphaltene and wax contents are given in Table 3-3. Luno II expresses low wax content comparable to Johan Sverdrup, and an intermediate content of asphaltenes compared to the chosen oils. Compared to other Norwegian crude oils, Luno II exhibits medium asphaltene content and low wax content.

min

5 10 15 20 25 30 35 40

counts

0 10000 20000 30000 40000 50000

FID1 A, (I:\HPCHEM\1\DATA\661196\STATFJ01.D)

nC-9 nC-11 nC-13 nC-15 nC-17 nC-18 nC-20 nC-25 nC-30

5 10 15 20 25 30 35 min

counts

4000 6000 8000 10000 12000 14000 16000 18000

FID1 A, (661073\GRANE001.D)

nC-11 nC-13 nC-15 nC-17 nC-18 nC-20 nC-25 nC-30+Pristane Phytane

Grane (1997-0253) Statfjord A (2000-0036)

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Table 3-3: Asphaltene (“hard”) and wax content for different crude oils and evaporated fractions Oil Residue Asphaltenes

"hard"

(wt. %)

Wax (wt. %)

Luno II

Fresh 0.5 2.7

150°C+ 0.6 3.4

200°C+ 0.7 3.9

250°C+ 0.8 4.4

Edvard Grieg

Fresh 0.2 3.9

150°C+ 0.2 4.8

200°C+ 0.3 5.4

250°C+ 0.3 6.0

Ivar Aasen

Fresh 0.1 4.0

150°C+ 0.1 4.7

200°C+ 0.2 5.3

250°C+ 0.2 6.2

Johan Sverdrup

Fresh 1.8 2.9

150°C+ 1.9 3.2

200°C+ 2.1 3.4

250°C+ 2.2 3.7

Grane

Fresh 1.4 3.5

150°C+ 1.4 3.9

200°C+ 1.4 4.3

250°C+ 1.5 4.8

Statfjord A

Fresh 0.1 4.3

150°C+ 0.1 5.5

200°C+ 0.1 6.4

250°C+ 0.1 8.3

Physical properties of fresh and weathered residues

Physical properties of Luno II and the other crude oils are listed in Table 3-4. Luno II has a slightly higher evaporative loss compared to Edvard Grieg, Ivar Aasen and Statfjord A, and the highest among the presented oils. The density of fresh Luno II is similar to Edvard Grieg while the 250°C+ residue of Luno II has a density similar to the 250°C+ residue of Johan Sverdrup.

Luno II flash points are in general lower compared to the other oils, likely due to higher content of the most volatile components. The pour points of Luno II are comparable to those of Ivar Aasen. The viscosities of the water free residues of Luno II are in the same range as Edvard Grieg, Johan Sverdrup and Statfjord A.

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Table 3-4: Physical parameters of Luno II in comparison with other Norwegian crude oils Oil type Residue Evap. (vol. %) Residue

(wt. %) Density (g/ml)

Flash point (°C)

Pour point (°C)

Visc.

(mPas) 5˚C (10 s^-1)

Visc.

(mPas) 13˚C (10 s^-1)

IFT (mN/m)

Luno II

Fresh 0 100 0.851 - -27 22 11 18

150°C+ 25 79 0.898 32 6 474 99 18

200°C+ 36 69 0.915 69 12 2689 569 21

250°C+ 45 61 0.931 108 18 10572 3165 20

Edvard Grieg

Fresh 0 100 0.850 - 6 138 30 -

150°C+ 22 82 0.883 46 15 955 207 -

200°C+ 32 72 0.897 85 21 5310 1150 -

250°C+ 40 64 0.908 112 27 9800 2350 -

Ivar Aasen

Fresh 0 100 0.838 - -6 65 9 17

150°C+ 18 85 0.861 42 9 210 34 18

200°C+ 29 75 0.872 75 15 950 170 18

250°C+ 39 65 0.883 113 21 3810 770 -

Johan Sverdrup

Fresh 0 100 0.891 - 3 309 61 19

150°C+ 12 91 0.915 45 9 1243 281 19

200°C+ 18 85 0.924 76 6 2530 632 19

250°C+ 26 78 0.935 110 12 9449 2044 21

Grane

Fresh 0 100 0.942 26 -24 1330 638 -

150°C+ 3 98 0.948 70 -18 1980 962 -

200°C+ 5 96 0.950 92 -15 2830 1084 -

250°C+ 13 89 0.960 139 -6 5970 3229 -

Statfjord A Fresh 0 100 0.827 - 0 - 43 -

150°C+ 22 79 0.868 - 12 - 832 -

200°C+ 34 68 0.883 - 21 - 1697 -

250°C+ 42 52 0.896 - 27 - 2894 -

-: No data available

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3.1.2 Emulsifying properties of Luno II

The emulsifying properties of Luno II were studied by use of the rotating cylinders (Hokstad et al., 1993).

Figure 3-3 and Figure 3-4 show examples of emulsions in the rotating cylinders at 13 °C and 5 °C, respectively. Luno II formed stable brownish emulsions at both temperatures and for all residues. The emulsions formed from 150°C+ and 200°C+ residues at 13 °C had a mousse-like appearance and consistency, and this was also true for the emulsions from the 150°C+ residue at 5 °C. The emulsions made from the heavier residues did not obtain this mousse consistency but formed a stable emulsion layer, as seen in the lower picture in Figure 3-3.

Figure 3-3: Emulsions formed after 24 hours at summer temperature (13 °C)

Four flasks on the left: Emulsions formed at 13 °C from the 150°C+

residue after 24 hours of rotation Two flasks on the right: Emulsions formed at 13 °C from the 200°C+

residue after 24 hours of rotation

Two flasks on the left: Emulsions formed at 13 °C from the 200°C+

residue after 24 hours of rotation Four flasks on the right: Emulsions formed at 13 °C from the 250°C+

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Figure 3-4: Emulsions formed after 24 hours at winter temperature (5 °C)

Water uptake and maximum water content

The parameters for kinetics (rate of water uptake) and maximum water uptake were studied by use of the rotation cylinders. The water contents in the water-in-oil emulsions as a function of time are shown in Table 3-5 and Table 3-6. The constant T1/2, which is derived from the tabulated data, is defined as the time (hours) required to incorporate half the maximum water quantity, and is used as input to the Oil Weathering Model (OWM). The water uptake is slower at 5 °C than at 13 °C, as is expressed by the higher T1/2 values for 5 °C.

The maximum water uptake is overall higher at 13 °C, between 70-85 vol. %. At 5 °C maximum water uptake reached 56 vol. % for the 250°C+ residue.

Four flasks on the left: Emulsions formed at 5 °C from the 150°C+

residue after 24 hours of rotation Two flasks on the right: Emulsions formed at 5 °C from the 200°C+

Two flasks on the left: Emulsions formed at 5 °C from the 200°C+ residue after 24 hours of rotation

Four flasks on the right: Emulsions formed at 5 °C from the 250°C+ residue after 24 hours of rotation

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Table 3-5: Water uptake of the evaporated residues of Luno II crude oil in rotating flasks at 13 °C Mixing time 150^oC +

(Vol. % water) 200^oC +

(Vol. % water) 250^oC + (Vol. % water)

Start 0 0 0

5 min 36 25 10

10 min 48 33 10

15 min 56 40 10

30 min 68 50 24

1 hour 75 59 40

2 hours 91 68 54

4 hours 87 76 63

6 hours 84 81 66

24 hours 83 80 71

T 1/2 0.14 0.29 0.93

Table 3-6: Water uptake of the evaporated residues of Luno II crude oil in rotating flasks at 5 °C Mixing time 150^oC +

(Vol. % water) 200^oC +

(Vol. % water) 250^oC + (Vol. % water)

Start 0 0 0

5 min 31 13 24

10 min 45 14 21

15 min 50 16 21

30 min 61 25 23

1 hour 69 43 2

2 hours 75 56 25

4 hours 84 65 43

6 hours 83 69 47

24 hours 82 75 56

T 1/2 0.18 0.88 2.00

Stability and efficiency of emulsion breaker

The stability of the emulsions from the weathered residues of Luno II crude oil was tested by quantifying the amount of water released from the emulsion during 24 hours of settling after 24 hours of rotation. In addition, the efficiency of emulsion breaker (Alcopol O 60 %) was evaluated. The results are given in

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Table 3-7 for both 5 °C and 13 °C.

Luno II forms stable emulsions at both winter and summer temperatures. The application of emulsion breaker resulted in only partial dehydrations of the emulsions. The higher concentration (2000 ppm) of emulsion breaker was in general more effective than the lower concentration (500 ppm), at both temperatures.

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Table 3-7: Stability of Luno II emulsions (no emulsion breaker) and efficiency of emulsion breaker at 5

°C and 13 °C

Residue Emulsion breaker Water-in-oil emulsion (vol. %) at 5 °C Water-in-oil emulsion (vol. %) at 13 °C Reference 24 hours * Stability

ratio** Reference 24 hours * Stability ratio**

150ºC+ none 82 81 0.99 83 83 1.00

200ºC+ none 75 76 1.00 80 80 1.00

250ºC+ none 56 57 1.00 71 71 0.98

150ºC+ Alc. O 60 % 500 ppm 82 75 0.67 83 74 0.60

200ºC+ Alc. O 60 % 500 ppm 75 69 0.74 80 70 0.61

250ºC+ Alc. O 60 % 500 ppm 56 57 1.00 71 62 0.65

150ºC+ Alc. O 60 % 2000 ppm 82 54 0.26 83 46 0.18

200ºC+ Alc. O 60 % 2000 ppm 75 35 0.18 80 42 0.19

250ºC+ Alc. O 60 % 2000 ppm 56 45 0.66 71 67 0.82

ppm: parts per million

*: w/o emulsion after 24 hours rotation and 24 hours settling

** Stability ratio of 0 implies a totally unstable emulsion after 24 hours settling; all the water is settled out during 24 hours settling. Stability ratio of 1 implies a totally stable emulsion.

Viscosity of water free residues and emulsified residues Table 3-8 and

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Table 3-9 give the viscosities of oil residue fractions with different water concentration (water free, 50 vol.

%, 75 vol. % and max. water) at 5 °C and 13 °C, respectively. As a non-Newtonian fluid, the viscosities of Luno II oil and emulsions are dependent on the shear rate; the viscosities are higher at a lower share rate (10 s^-1) compared to higher shear rate (100 s^-1). This decrease in viscosity with increasing shear rate is likely caused by breaking up the wax lattice structure with increased mechanical force.

Table 3-8: Viscosity of Luno II water free residues and emulsified residues at 5 °C Residue Water

content (vol. %)

Viscosity (mPas) 10 s^-1 100 s^-1

Fresh 0 22 20

150°C+ 0 474 269

200°C+ 0 2689 1052

250°C+ 0 10572 3173

150°C+ 50 1235 785

200°C+ 50 5289 2282

250°C+ 50 21369 3309

150°C+ 75 5259 1711

200°C+ 75 21944 3995

250°C+ 75 -* -*

150°C+ 82 36215 3994

200°C+ 75 20165 4029

250°C+ 55** 25459 2388

*: The 250°C+ residue did not obtain 75 vol. % water-in-oil emulsion at 5 °C, max. water uptake was 55 vol.

% .

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Table 3-9: Viscosity of Luno II water free residues and emulsified residues at 13 °C Residue Water

content (vol. %)

Viscosity (mPas) 10 s^-1 100 s^-1

Fresh 0 11 11

150°C+ 0 99 76

200°C+ 0 569 361

250°C+ 0 3165 1392

150°C+ 50 529 415

200°C+ 50 1904 1074

250°C+ 50 9615 3152

150°C+ 75 2105 574

200°C+ 75 6227 1637

250°C+ 75 - -

150°C+ 83 20155 2648

200°C+ 80 23888 4094

250°C+ 71 24632 4208

*: The 250°C+ residue did not obtain 75 vol. % water-in-oil emulsion at 13 °C, max. water uptake was 71 vol. %

3.1.3 Chemical dispersibility

The dispersibility testing included:

• Screening of five different dispersants to find the best and relevant dispersant for the Luno II oil.

• Dosage testing of the best/relevant dispersant.

• Systematic dispersant study with the best dispersant at the optimal dosage rate (DOR - Dispersant to Oil Ratio), to determine the time window for effective dispersant use on the Luno II oil in a spill scenario.

Screening and dosage study of dispersants

A screening study was performed using the low energy test (IFP) to investigate the effectiveness of different dispersants and the optimal dose rate (DOR = Dispersant to Oil Rate, by weight).

The dosage testing was conducted at 13 °C with the 200°C+ residue emulsified with 50 vol. % water, and different DORs of 1:25, 1:50, 1:100, and 1:200. Results from the screening study are given in Table 3-10, while results from the dose rate testing are given in

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Table 3-11. The dose rate testing was conducted using both the low energy test (IFP) and the high energy test (MNS).

Table 3-10: Screening test of dispersants on Luno II crude oil at 13 °C using the MNS & IFP tests Dispersant

(DOR 1:25)

IFP MNS

Efficiency dispersant

200°C+ /50 vol. % Efficiency dispersant 200°C+ /50 vol. %

Corexit 9500 82 100

Dasic NS 66 100

Finasol OSR 62 54 -

Gamlen OD 4000 51 -

Superdispersant 33 -

- Not tested:

The viscosity for screening testing was 1904 mPas (10s^-1) at 13 °C for the 200^oC+ 50 vol. % emulsion.

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Table 3-11: Dosage rate testing of Dasic NS on Luno II crude oil at 13 °C Dispersant

(dosage rate)

Efficiency of dispersant on 200°C+/50 vol. % emulsion

IFP

Efficiency of dispersant on 200°C+/50 vol. % emulsion

MNS

Viscosity (mPas) 10 s^-1, 13°C

Dasic NS (1:25) 66 100 1904

Dasic NS (1:50) 45 100 1911

Dasic NS (1:100) 22 100 1911

Dasic NS (1:200) 8 94 1911

The results of the screening test showed that Corexit 9500 was the most effective dispersant in the low energy IFP-test. However, Dasic NS was chosen for further testing since this dispersant had promising effectiveness and is currently in use in Norway. Consequently, the dosage test and continued dispersibility testing were performed with Dasic NS.

As can be seen in

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Table 3-11, the dosage rate test showed varied dispersibility effectiveness. The IFP-test is a low energy (non- breaking waves) test, while the MNS-test represents a high energy system (breaking waves). The additional energy in the MNS-test provides a higher degree of natural dispersion, thus explaining the higher effectiveness.

The dosage of 1:25 was the most effective as observed for the IFP-test, while the lower dosages gave decreasing effectiveness.

Window of opportunity for use of dispersant on Luno II crude oil

Dasic NS is the dispersant agent currently in the NOFO stock, and is considered to be the operational target agent when applying dispersant on a marine oil spill. A dosage rate of 1:25 (4 wt. %) is the standard procedure used to establish the time window for dispersant application.

Results from the systematic dispersibility study at 5 °C and 13 °C are given in Table 3-12 and Table 3-13, respectively.

Table 3-12: Efficiency of Dasic NS on weathered oil / emulsions of Luno II at 5 °C Residue Water content

(vol. %) Viscosity (mPas)

10 s^-1 Viscosity (mPas)

100 s^-1 IFP MNS

Efficiency (%) Efficiency (%)

150°C+ 0 474 269 77 100

200°C+ 0 2689 1052 13 100

250°C+ 0 10572 3173 0 32

150°C+ 50 1235 785 66 100

200°C+ 50 5289 2282 4 100

250°C+ 50 21369 3309 2 -

150°C+ 75 5259 1711 32 71

200°C+ 75 21944 3995 3 52

250°C+ 75 - - - -

150°C+ 82 36215 3994 4 51

200°C+ 75 20165 4029 2 5

250°C+ 55 25459 2388 1 1

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Table 3-13: Efficiency of Dasic NS on weathered oil / emulsions of Luno II at 13 °C Residue Water content

(vol. %) Viscosity (mPas)

10 s^-1 Viscosity (mPas)

100 s^-1 IFP MNS

Efficiency (%) Efficiency (%)

150°C+ 0 99 76 80 100

200°C+ 0 569 361 62 100

250°C+ 0 3165 1392 10 100

150°C+ 50 529 415 80 100

200°C+ 50 1904 1074 66 100

250°C+ 50 9615 3152 6 61

150°C+ 75 2105 574 74 75

200°C+ 75 6227 1637 30 47

250°C+ 75 - - - -

150°C+ 83 20155 2648 23 21

200°C+ 80 23888 4094 8 7

250°C+ 71 24632 4208 3 5

The criteria for estimation of dispersibility effectiveness are listed in Table 3-14 along with the estimated viscosity limits for use of dispersants on Luno II emulsions. The viscosity limits are estimated from Figure 3-5.

Table 3-14: Estimated viscosity limits for use of dispersant for Luno II emulsion and the criteria for definition of time window

Dispersibility Criteria (wt. %)

Dispersibility limits based on oil viscosites (mPas = cP)*

Chemically dispersible IFP efficiency > 50 % 3000 Not chemically

dispersible MNS efficiency < 5 % 25000

* Estimated limits are based on the dispersibility data from both the low energy IFP-test and the high energy MNS-test

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Figure 3-5: Dispersant effectiveness on Luno II crude oil and its weathered residues at 5 °C and 13 °C

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3.2 Meso-scale laboratory testing results

The meso-scale testing gives valuable operational information about the oil's behaviour under more realistic conditions, and the flume-testing is therefore a supplement to the small-scale testing. The experimental results obtained for Luno II in the meso-scale laboratory test are presented below. Table 3-15 and

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Table 3-16 show the results from the meso-scale experiments at 5°C and 13°C, respectively.

Table 3-15: Results from the meso-scale weathering experiment of Luno II at 5 °C Sample no Time Water content Evaporative loss Viscosity Oil in water

(hours) (vol. %) (wt. %) (mPas), 10 s^-1 ppm*

1 0.5 77 18 243 57

2 1 75 21 539 59

3 2 74 24 2355 63

4 4 75 27 3573 62

5 6 74 29 4705 46

6 12 74 31 6997 31

7 24 75 33 12065 17

8 48 74 35 17655 11

9 72 74 36 21107 7

1^st application of dispersants: 52 g Dasic NS (DOR = 1.1 wt. %)

3 min. disp 1 - - - - 13

10 min. disp 1 - - - - 27

60 min. disp 1

2^nd Application of dispersants: 49 g Dasic NS (DOR= 1.1 wt. %)

3 min. disp 2 - - - 11218 33

10 min. disp 2 - - - - 62

30 min. disp 2 - - - - 63

120 min. disp 2 - - - - 75

240 min. disp 2 - - - - 63

-: no measured data. *:ppm=parts per million

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Table 3-16: Results from the meso-scale weathering experiment of Luno II at 13 °C Sample no Time Water content Evaporative loss Viscosity Oil in water

(hours) (vol. %) (wt. %) (mPas), 10 s^-1 ppm*

1 0.5 68 22 279 76

2 1 74 25 428 86

3 2 75 29 1237 88

4 4 78 31 3204 73

5 6 82 32 5879 37

6 12 83 34 7786 36

7 24 80 36 11504 16

8 48 81 39 19670 9

9 72 79 40 23401 30

1^st application of dispersants: 50 g Dasic NS (DOR = 1.1 wt. %)

3 min. disp 1 - - - - 22

10 min. disp 1 - - - - 19

60 min. disp 1 - - - - -

2^nd Application of dispersants: 50 g Dasic NS (DOR= 1.1 wt. %)

3 min. disp 2 - - - 20648 27

10 min. disp 2 - - - - 26

30 min. disp 2 - - - - 29

120 min. disp 2 - - - - 31

-: no measured data. *:ppm=parts per million

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3.2.1 Evaporation

Figure 3-6 shows the evaporative loss obtained in the meso-scale experiments compared to the values predicted by the SINTEF oil weathering model (OMW). The predictions correspond well with the measured evaporative loss.

Figure 3-6: Predicted evaporative loss for Luno II with the results from the meso-scale experiments at 5

°C and 13 °C

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3.2.2 Water uptake

In Figure 3-7 the water uptake predicted by SINTEF OWM is shown along with the measured water uptake from the flume experiments. As can be seen, the measured maximum water content was somewhat higher in both the experiments compared to the OWM predictions. As the emulsions were not stable with large water droplets during the first hours of weathering, the water content is more unreliable and explains why the flume experiments indicate a more rapid water uptake compared to the OWM predictions.

Figure 3-7: Predicted water uptake for Luno II and the results from the meso-scale experiments at 5 °C and 13 °C

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The measured emulsion viscosities are presented in Figure 3-8 along with the predicted emulsion viscosities from SINTEF OWM. The predicted viscosities corresponded very well with the measured viscosities, at both test temperatures (5 °C and 13 °C).

Figure 3-8: Predicted emulsion viscosities for Luno II with the results from the meso-scale experiments at 5 °C and 13 °C

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3.2.3 Mass balance

The main elements in the mass balance for a crude oil spilled at sea are:

• evaporative loss

• surface oil

• dispersed oil

Because the initial oil sample and water volume in the flume are reduced throughout the test, the following parameters must be taken into consideration:

• amount of oil sampled

• amount of water sampled

• amount of oil sticking to the flume wall

The amount of oil evaporated, oil on surface, dispersed and sampled oil was calculated, and the oil adsorbed to the flume walls was estimated. Table 3-17 shows values for the mass balance of Luno II during weathering in flume experiments after 24 hours.

Table 3-17: Mass balance for Luno II during the meso-scale laboratory tests at 5 °C and 13 °C (after 24 hours of weathering)

Mass balance (% of initial oil) 5ºC 13ºC

Evaporated 33 36

Oil on water surface 60 56

Dispersed oil 1 1

Sampled amount of oil 2 2

Oil adsorbed to the flume walls 4 5

Figure 3-9: Mass balance of Luno II in the 5 °C meso-scale laboratory test before the application of dispersant

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Figure 3-10: Mass balance of Luno II in the 13 °C meso-scale laboratory test before the application of dispersant

3.2.4 In situ chemical dispersion

After 72 hours of weathering, the chemical dispersant Dasic NS was applied by spraying it twice on the water-in-oil emulsion (in situ application). The dosage ratios are given in Table 3-18.

Table 3-18: Dispersant dosage rates used in Luno II meso-scale experiment (in situ application) Test temperature

(°C) Dasic NS

application (g)

Dispersant to Oil Ratio (DOR), wt. %

Dispersant to Emulsion Ratio (DER), wt. %

5 52 1.1 0.3

5 49 1.1 0.3

13 50 1.1 0.2

As the effect of the first application of dispersant was low, the dispersant was applied twice in each experiment. In both experiments water samples were taken at

• 3 and 10 minutes after the first application

• 3, 10, 30 and 120 minutes after the second application

An additional water sample was taken after 240 minutes in the 5 °C experiment.

3.2.5 Visual observations

When released onto the sea water in the meso-scale flume, the Luno II crude oil rapidly formed unstable emulsions with large water droplets (free water). The emulsions became more stable during the first 24 hours of weathering in the flume. The colour of the emulsion turned from dark brown to a reddish brown colour during the first 24 hours of weathering, and became more light brownish after three days of weathering.

A relatively high amount of oil was available for chemical dispersion, as shown in the mass balance (Table 3-17).The oil dispersed poorly and a sizable slick remained on the surface throughout the whole experiment.

The dispersant (Dasic NS) broke up the slick in to smaller lumps instead of the one continuous sheet of

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emulsion observed during the first 3 days. However, in the 5 °C test these smaller lumps reformed a slick between two hours and four hours after dispersant application. The results indicated that a higher dosage could be applied on the slick in an oils spill situations at both temperatures.

A selection of pictures taken at the various sampling times from both tests, are presented below. The dissimilarities in colour within the same sample times are due to photographing at different angles; the pictures to the left were taken from a near vertical position relative to the flume surface while the pictures to the right were taken at an angle and depict the oil and emulsions lit by the artificial light. Pictures taken after addition of dispersant are all taken at an angle.

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Pictures taken during the 5 °C experiment

Start (Time = 0)

1 hour after oil release

6 hours after oil release

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3 days after oil release

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In situ application of dispersant (Dasic NS), 5 °C

0 minutes after 1^stdispersant application 10 minutes after 1^stdispersant application

0 minutes after 2^nd dispersant application 30 minutes after 2^nd dispersant application

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Pictures taken during the 13 °C experiment:

Start (Time = 0)

1 hour after oil release

6 hours after release

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3 days after oil release

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In situ application of dispersant (Dasic NS), 13 °C

0 minutes after 1^stdispersant application 10 minutes after 1^stdispersant application

120 minutes after 2^nd dispersant application

Luno II crude oil - properties and weathering at sea - related to oil spill response

Report

Luno II crude oil – properties and weathering at sea

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Report

Luno li crude oil - properties and weathering at sea

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Document history

Table of contents

1 Executive summary

2 Introduction

3 Experimental results

3.1 Small-scale laboratory testing results

3.1.1 Chemical composition and physical properties

3.1.2 Emulsifying properties of Luno II

3.1.3 Chemical dispersibility

3.2 Meso-scale laboratory testing results

3.2.1 Evaporation

3.2.2 Water uptake

3.2.3 Mass balance

3.2.4 In situ chemical dispersion

3.2.5 Visual observations