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STUDY TITLE: Physical and Chemical Analyses of Crude and Refined Oils: Laboratory and Mesoscale 

Oil Weathering

REPORT TITLE: Physical and Chemical Analyses of Crude and Refined Oils: Laboratory and 

Mesoscale Oil Weathering

CONTRACT NUMBER: M14PC00012

SPONSORING OCS REGION: Alaska

APPLICABLE PLANNING AREA: Beaufort Sea, Chukchi Sea, Cook Inlet

FISCAL YEARS OF PROJECT FUNDING: FY 2014-2016

COMPLETION DATE OF REPORT: 

COSTS BY FY: FY 2014: $ 580,511

CUMULATIVE PROJECT COST: $ 580,511

PROJECT MANAGER: A. H. Walker

AFFILIATION: SEA Consulting Group

ADDRESS: 325 Mason Ave., Cape Charles, VA 23310

PRINCIPAL INVESTIGATOR(S)*: K.R. Sørheim

AFFILIATION: SINTEF Materials and Chemistry

ADDRESS: Postboks 4760 Sluppen, 7465 Trondheim, NORWAY 

KEY WORDS: Alaska North Slope; Alaska OCS (Outer Continental Shelf); crude oils; refined oils; Wide 

Range Gasoil (WRG); Marine Gasoil (MGO; Automotive Diesel Oil (ADO); characterization; weathering; 

emulsion; dispersant; Oil Weathering Model (OWM).

BACKGROUND: The Bureau of Ocean Energy Management (BOEM) addressed this specific project to 

expand and update the oil data set in the oil-weathering model (OWM) by analyzing oil weathering in the 

laboratory. The BOEM Alaska OCS Region uses the Oil Weathering Model (OWM) tool to provide a 

quantitative set of spill weathering parameters for use in NEPA assessments. Weathering of spilled oil and 

persistence of its individual components vary depending on the specific characteristics of the oil. Currently, 

the analysts in the Alaska OCS Region use information about oil weathering to make estimates regarding 

the mass balance of an oil spill through time. The new data is also relevant and important for oil spill 

preparedness and response on the Alaska OCS regulated by the US agency Bureau of Safety and 

Environmental Enforcement (BSEE).

OBJECTIVES: (1) To obtain weathering characteristics of crude oils representative of the Alaska OCS 

(Outer Continental Shelf) and typical refined products transported in offshore waters; 

(2) To expand libraries of oil compositions of existing weathering models such as the SINTEF Oil 

Weathering Model (OWM) and the Automated Data Inquiry for Oil Spills (ADIOS) model from the National 

Oceanic and Atmospheric Administration (NOAA). 

DESCRIPTION:

SINTEF Materials and Chemistry was asked by SEA Consulting Group to conduct weathering studies

including physical and chemical analysis of six oils. The oils included:

 Three crude oils supplied from the Alaska North Slope: Alpine and Kuparuk (ConocoPhillips Alaska, 

Inc.) and Northstar (Hilcorp Alaska, LCC),
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 Two light refined products of ADO (Automotive Diesel Oil, also called Ultra-Low Sulphur Diesel 

(ULSD) and MGO (Marine Diesel Oil) supplied from the Esso Slagen refinery in Norway, and a 

Wide Range Gasoil (WRG) supplied from the Statoil Mongstad refinery, Norway.

The study of the six oils included both bench-scale and meso-scale flume laboratory testing conducted at 

a temperature of 10 °C, reflecting relevant sea temperature in Alaska OCS waters. The standardized benchscale testing included topping/distillation of the oils into 150, 200 and 250C+ residues to determine the 

percentage of evaporative loss and remaining residual after topping. The fresh oil and its corresponding

residues were characterized for physical and chemical properties as density, pour point, flash point, 

interfacial tension, viscosity, wax and asphaltenes, and distribution of hydrocarbons on gas 

chromatography (GC/FID). The emulsification studies on the residues were conducted by use of rotating 

cylinders (24 hours of rotating time) to determine the kinetics of water uptake, preparing 50 and 75 volume

% and maximum water-in-oil emulsions, and determine stability of emulsions and measurements of 

emulsion viscosities. In addition, the oils were weathered in the meso-scale flume basin for 2-3 days and 

surface samples and water samples were taken during the experiments. The surface samples included 

measurement of viscosities, quantifying the amount of water in the oil and determining evaporative loss, 

and quantifying dispersed oil in the water samples. Dispersant effectiveness testing was beyond this study’s 

scope, however, SINTEF added Corexit 9500 to the emulsified oils at the end of the testing to obtain a 

visual assessment of potential dispersibility in their weathered state. The experimental data obtained in the 

laboratory testing were further customized and tabulated as input parameters to numerical Oil Weathering 

Models in order to obtain reliable and robust weathering predictions of oil spill scenarios. 

SIGNIFICANT CONCLUSIONS:

Overall, the weathering studies including physical and chemical analysis of the six oils (three crude oils and 

three refined products) gave consistent data as a basis for input to two specified oil weathering models, 

e.g., SINTEF’s OWM and NOAA’s ADIOS. The weathering experiments in the meso-scale flume basin 

should be regarded as supplementary to the bench-scale testing. Together, data from both testing scales 

offer valuable operational information about the possible fate and effects of dispersant use. Laboratory data 

generated both in the bench-scale and meso-scale experiments was evaluated and prepared for input to 

the oil weathering models. However, modelling of oil weathering and assessment of the output predictions 

of physical oil weathering properties were not a part of this project.

STUDY RESULTS:

When weathered on the sea surface, oils undergo changes that affect behavior and oil spill 

countermeasures in various ways, as a function of time and environmental conditions. The formation of 

water-in-oil emulsion and the physical properties of oil can change significantly with increasing of viscosities

that also increase the volume of the spilled oil. The six oils from this study were analyzed for their weathering 

properties including physical and chemical characterization in a standardized bench-scale methodology. In 

addition, the weathering of the oils was also studied in the meso-scale flume basin as supplementary to the 

bench-scale testing for all oils. The obtained laboratory data of the six oils were customized and tabulated 

as input data for the SINTEF OWM and ADIOS oil weathering models which are used to predict weathering 

properties of oils at sea. 

Properties of crude oils from Alaska North Slope:

Alpine is a paraffinic crude oil with a density of 0.832 g/mL (corresponds to API° 38.4). The fresh 

unweathered oil has a very low pour point (<-36 °C), but increases rapidly with the evaporative loss. The 

oil has a medium to low wax content of 2.1 wt. %, and has asphaltene content of 0.46 wt. %. The laboratory 

study showed that the oil forms stable water-in-oil (w/o) emulsions when weathered. In order to effectively 

dehydrate the emulsion when using emulsion breaker (Alcopol O 60 %), a minimum dosage of 2000 ppm 

should be applied. After three days of weathering in the flume basin (meso-scale experiments), Corexit 

9500 (in-situ application) was added to the emulsion to finalize the testing. The oil/emulsion showed a 

significant potential for dispersant use as a response option. However, effectiveness testing and 

determining the specific time-window, or window of opportunity, for dispersant use was not part of this 

project.

Kuparuk is categorized as a high-density 0.917 g/mL (API° 22.7) asphaltenic (4.7 wt. %) crude oil with a 

relatively low wax content of 1.3 wt. %. Kuparuk has a low pour point and solidification on the sea surface 
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is not anticipated since solidification typically arises with pour points 10-15 °C above the sea temperature. 

The crude oil formed stable w/o-emulsions particularly for the 200 and 250°C+ residues with high 

viscosities. In general, the emulsions require a high dosage of emulsion breaker (Alcopol O 60 % at 2000 

ppm) in cases where emulsion breaker might be added as part of a mechanical recovery operation to settle 

out water and decrease the storage volume needed. After three days of weathering in the meso-scale flume 

basin, Corexit 9500 (in-situ application) with a cumulative dosage Dispersant-to-Oil (DOR) ratio of 1:50 was 

added to the oil/emulsion. The findings indicate that a higher dosage (DOR > 1:50) is recommended to be 

applied to a slick in an oil spill situation for higher effect, since the efficiency of adding dispersant (DOR 

1:50) was not optimal. However, the window of opportunity for use of dispersant as a function of 

effectiveness and viscosities, and dosage testing for optimal DOR, was not determined in this study.

Northstar is a very light paraffinic crude oil with a density of 0.779 g/ml (API° 50), and exhibits low content 

of wax (1.7 wt. %) and asphaltenes (0.03 wt. %). The oil is a low-emulsifying crude oil that forms loose 

emulsions and easily released water with the addition of a concentration of 500 ppm of the emulsion breaker

(Alcopol O 60 %). The oil showed high potential for application of dispersant agent (Corexit 9500) based 

on the results from the meso-scale flume basin. However, no laboratory study was conducted to assess 

the window of opportunity for using chemical dispersant on this oil.

Properties of refined products:

The ADO (Automotive Diesel Oil) has a density of 0.830 g/mL (corresponds to API° 38.8). The ADO oil has 

a very low content of wax and asphaltenes; less than 0.05 wt. %. The diesel oil has a very low pour point 

(<-36 °C) and remained low with evaporative loss. The weathered oil residue did not emulsify during the 

bench-scale emulsifying testing and showed no water uptake. Based on visual inspection during the mesoscale flume experiment a great majority of the oil was naturally dispersed into the water column, and only 

a minor amount of the oil was observed on the surface after three days of weathering (~ 3 % of the total 

released oil into the flume). The remaining oil on the surface became darker with a "slimy" characteristic. 

The dispersant Corexit 9500 (in-situ application) was added and visually showed that the dispersant was

effective. 

The MGO (Marine Gasoil) has a density of 0.849 g/mL (corresponds to API° 35). The MGO oil has a higher 

wax content (1.96 wt. %) compared with the ADO. The asphaltene content of the diesel oil is less than 0.05 

wt. %. The MGO has a low pour point similar to the ADO. The oil did not emulsify (no significant water 

uptake) in the bench-scale laboratory testing. During the meso-scale testing, most of the oil was easily 

naturally dispersed and diluted into the water column during the two days of weathering, and no dispersant 

agent was therefore applied onto the surface in the flume due to insignificant amount of available surface 

oil.

The WRG (Wide Range Gasoil) has a density of 0.892 g/mL (corresponds to API° 27) with a medium 

content of wax (4.8 wt. %) and with low content of asphaltenes (0.05 wt. %). The WRG oil has a low pour 

point (<-24 °C). Due to lack of lighter compounds, less than 250 °C, the fresh oil was assumed to have 

similar weathering properties as for the 250°C+ residue. The oil showed emulsifying properties during the 

bench-scale testing, but the emulsions were very unstable and easily broke up after standing less than an 

hour. Based on the meso-scale flume experiment a larger amount of the oil was naturally dispersed into 

the water column, and only a minor amount of the oil was observed on the surface after two days of 

weathering. However, the dispersant agent Corexit 9500 (in-situ application) was added on the surface 

slick and visually showed high efficiency.

STUDY PRODUCTS:

Sorheim, K.R. 2016. Physical and Chemical Analyses of Crude and Refined Oils: Laboratory and 

Mesoscale Oil Weathering. OCS Study BOEM 2016-062. Prepared by SINTEF Materials and Chemistry 

and SEA Consulting Group for the USDOI, Bureau of Ocean Energy Management, Alaska OCS Region. 

Anchorage, AK. 107 pp.

*P.I.’s affiliation may be different than that listed for Project Manager(s).
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Location of Alpine, Kuparuk and Northstar crude oils Source:

http://www.eia.gov/todayinenergy/detail.cfm?id=21632

Location of Esso Slagen Refinery in the South-East of Norway situated on the west bank of 

the Oslo fjord. Source: news.exxonmobil.com

Location of Statoil Mongstad Refinery at the west coast of Norway. Source: 

http://www.statoil.com/en/ouroperations/terminalsrefining/prodfacilitiesmongstad/pages/energiver

kmongstad.aspx