“The characteristics of an individual grade of crude oil are defined in an analysis called an assay …” ¹⁾

• properties of a crude oil important to a refinery ²⁾
• expected yields of various finished products ³⁾
• density, sulfur content, acidity, viscosity ⁴⁾
• reservoir, oilfield, location ⁵⁾

Crude assay programs can be subdivided into various formats, one format being Whole Crude property measurements/inspections and the other being a full assay including distillations and inspection data. ⁶⁾

Also as a crude oil field ages property data will change. ⁷⁾

black, brown, straw coloured ⁸⁾

The ratio of different hydrocarbon molecules and other substances such as sulfur determines the color of crude, according to Foued Badrouchi, a doctoral student in the department of petroleum engineering at the University of North Dakota. ¹⁾

The oil's relative density, known as specific gravity, also affects the color, he said.

Lighter, or less-dense, crude tends to be more greenish-brown, another member wrote.

Bakken crude is a green color.

This crude from West Texas has a low specific gravity, said Ramiro Martinez, another group member, who shared the photo. That's why the liquid is almost translucent.

This crude is much lighter, which is why it looks nearly transparent.

“Light crude oil contains a large amount of liquid natural gas,” Badrouchi said. Liquid natural gas is essentially natural gas — namely, methane — that's been cooled down or pressurized into a liquid form.

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sulfur, nitrogen, water, metals, sediment ⁹⁾

⚠️ crude loaded in cold climate occupy larger volume in warmer climate / becomes less dense¹¹⁾

metric density (kg/m3) measured @ 15°C (60°F - most common T @ which crude density is measured) & 1 atm¹²⁾

measure density of oil in relation to the density of water¹³⁾

• API; hydrometer / Archimedes principle (amount of water displaced)¹⁴⁾
• Specific gravity (relative density; density of oil divided by density of water; g/cm3)¹⁵⁾

• water @60F and 1atm has s.g. = 1¹⁶⁾
• C3 has API > 100¹⁷⁾
• water has API = 10¹⁸⁾
• refining higher API crude oils will more easily generate a larger proportion of gasoline and other high value products (very little heavy products such as residual fuel oil and bitumen)¹⁹⁾

heavier; 38.3° API²⁰⁾

Hydrogen sulfide gas—H2S, for short—has a terrible propensity to evaporate from crude, knock out your olfactory capabilities, and slowly suffocate you to death.

If you inhale hydrogen sulfide in a concentration of 1,000 ppm (0.1 percent by volume) for only a few seconds, you will be dead.“

processed in the US
refineries have to remove sulfur form finished products using expensive hydrotreater units no hydrotreater / no crude above a certain sulfur content that can be used

• mercaptans (thiols; special treatment; distinct rotten egg odor; removed with sweetener unit; small amounts used as safety additive to normally odourless natural gas so that gas leaks can be easily detected)
• hydrogen sulfide
• thiophenes

waste product of biodegradation of crude by bacteria in reservoir; bacteria metabolize lighter oil molecules more easily; acidic crudes consist of remaining heavy HC molecules (for bacteria more challenging to digest) highly acidic crude is cheaper; acid must be neutralised; corrodes steel pipes acid content in crude measure by Total Acid Number (TAN) / Neutralisation number (mg of KOH needed to neutralise a gram of crude);

• most refineries TAN < 0.5
• TAN > 0.7 highly acidic crude (Chad's Doba, Angolan Hungo Stram, Angolan deepwater Kuito; North Sea Alba field)
• blend high TAN crude with lower TAN crudes

how easily a liquid resists flowing

water-like to near-solid

Water 🚰 1 - 5 cps

Blood 🩸 10 cps

Crude oil that has a high proportion of paraffin — a type of hydrocarbon — is thick and waxy, especially at low temperatures. This is an example of a heavier crude with a much higher relative density or higher specific gravity.

“All the crude out there is completely saturated with wax to the point that all the tanks are insulated and the oil has to be kept hot to transport,” he wrote on Facebook. “We aren't allowed to load it unless it's between 140-180 degrees Fahrenheit.”

• highly viscous material (e.g. honey) = large molecules (tangle as they pass each other)
• heavy crude = larger HC molecules = highly viscous
• changes with temperature ()

measured @ 40°C & 100°C (because density changes with temperature) viscous crude heated or blended (e.g. with kerosene) to flow through a pipeline

Poise … absolute/dynamic viscosity (no other force involved in the measure) of crude in reservoir

kinematic viscosity … outside reservoir conditions

Crude Oil Viscosity vs. Gravity²⁾

Je höher die Viskosität einer Flüssigkeit, desto dickflüssiger (z.B. Honig=hochviskos; Wasser=niedrigviskos)

Fluids with low viscosity have a low resistance and shear easily and the molecules flow quickly; high viscosity fluids move sluggishly and resist deformation.

Initial Boiling Point (IBP) The temperature at which the first drop of distillate appears after commencement of distillation in the standard ASTM laboratory apparatus. Final Boiling Point (FBP) The maximum temperature observed on the distillation thermometer when a standard ASTM distillation is carried out.

# Inspection

Care is needed in some geographic locations, in the sampling from the crude container, especially in hot climates. In this case, the container may need to be cooled prior to the measurement in order to insure that light ends are not lost. Conversely, in colder climates containers need to be brought up gradually to room temperatures.

# API Gravity

ASTM D287/1298

hydrometer method

insure that the crude aliquot taken is representative. API is measured along with the temperature of the crude that is then converted to an API at 60 °F

# Sulfur content

normally in the range of 0.1-5.0-wt %

measured utilizing an x-Ray technique such as the following two methods ASTM D4294 or D5291 using a technique known as X-Ray Fluorescence (analysis to be completed in about 3-5 minutes)

sulfur contents greater than 5.0 % are measured by methods such as D1552, a combustion technique

extremely low levels an Ultraviolet fluorescence technique is employed (ASTM D5453).

# Pour point

the temperature normally 3 degrees above the point a sample no longer moves when inverted

of particular importance for crudes that are transported through pipelines from source to load ports.

ASTM D5853 (crudes that have pour points greater than -36 °C)

ASTM D97 (crudes that have pour points lower than -36 °C)

# Whole Crude Simulated Distillation

done on 5 metre fused silica columns having thin film thickness allowing the analysis to be completed within an hour

true boiling point curve can be determined by plotting % off (cumulative yield) versus temperature.

https://ts.totalenergies.com/business-customers/crude-assays/
https://corporate.exxonmobil.com/crude-oils/crude-trading/assays-available-for-download
https://www.equinor.com/energy/crude-oil-assays
https://www.bp.com/en/global/bp-trading-and-shipping/documents-and-downloads/technical-downloads/crudes-assays.html
https://www.ineos.com/businesses/ineos-fps/business/forties-blend-quality/forties-blend/