Basic sediment and water (BS&W) is both a technical specification of certain impurities in

crude oil Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring u ...

and the method for measuring it. When extracted from an

oil reservoir A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in Porosity, porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by t ...

, the crude oil will contain some amount of water and

suspended solids Suspended solids refers to small solid particles which remain in suspension in water as a colloid or due to motion of the water. Suspended solids can be removed by sedimentation if their size or density is comparatively large, or by filtration ...

from the reservoir formation. The particulate matter is known as sediment or mud. The water content can vary greatly from field to field. It may be present in large quantities for older fields, or if oil extraction is enhanced using water injection technology. The bulk of the water and sediment is usually separated at the field to minimize the quantity that needs to be transported further. The residual content of these unwanted impurities is measured as BS&W.

Oil refineries An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefied pet ...

may either buy crude to a certain BS&W specification or may alternatively have initial crude oil dehydration and desalting process units that reduce the BS&W to acceptable limits, or a combination thereof. There are several ways to reduce the amount of water and sediment in crude oil. Gravity settling over several days allows water and solids settle out. Heating crude oil reduces its viscosity aiding further separation of these components. Certain chemicals added to crude oil can act to aid separation. Surfactants help water to separate from the oil. Paraffin thinners allow heavier fractions in the oil to flow more easily. Demulsifiers breakdown the oil/water emulsions that may have formed and thereby help to separate different elements of the crude oil.

Testing

ASTM ASTM International, formerly known as American Society for Testing and Materials, is a standards organization that develops and publishes voluntary consensus technical international standards for a wide range of materials, products, systems and s ...

method D4007 or

API An application programming interface (API) is a connection between computers or between computer programs. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how to build ...

Manual of Petroleum Measurement Standards chapter 10.4 are commonly used to measure BS&W. These methods both consist of mixing equal volumes of solvent and crude oil then centrifuging in order to separate any solids, free water, or suspended particles. More precise methods beyond BS&W are available to independently measure water or solids present in a sample of crude oil.

BS&W and Free Water in practice

All unrefined crude oil has some water entrained within it. During transportation by ship, separation occurs naturally and water collects at the base of the tank below the oil, this is known as free water (FW). Sales contracts for crude oil will typically specify the BS&W and FW to ensure the cargo meets quality standards. In one case in 2020 the quality documents required a BS&W of 0.2% and did not provide for any free water. Upon loading a Very Large Crude Carrier (VLCC) in Porto do Acu in Brazil, 4827 barrels of FW was measured. By the time the ship had reached its destination in the Far East, free water had settled and was measured at 8767 barrels. The BS&W parameter was thereby significantly exceeded.

References

Sources

* {{cite web, url= http://www.freshpatents.com/Steam-cracking-of-partially-desalted-hydrocarbon-feedstocks-dt20070104ptan20070004952.php, title= Steam cracking of partially desalted hydrocarbon feedstocks, accessdate= 2009-03-11, author= , date= , publisher= , archive-url= https://web.archive.org/web/20080725103050/http://www.freshpatents.com/Steam-cracking-of-partially-desalted-hydrocarbon-feedstocks-dt20070104ptan20070004952.php, archive-date= 2008-07-25, url-status= dead Industrial processes Chemical process engineering Oil refining