GB1562755A - Process for desalting crude petroleum - Google Patents

Description

(54) PROCESS FOR DESALTING CRUDE PETROLEUM (71) We, THE BRITISH PETRO LEUM COMPANY LIMITED, of Britannic House, Moor Lane, London, EC2Y 9BU, a British Company, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to a method of desalting and dehydrating crude petroleum.

In the production of crude petroleum, salt water can be co-produced with the crude petroleum and is separated from the crude petroleum. The amount of salt water produced relative to the crude petroleum varies with the age of the well and the nature of the oil- bearing structure. The co-produced salt water is separated from the crude petroleum to give a salt content of the crude petroleum of less than a given specification value e.g. 25 pounds per thousand barrels of sodium chloride equivalent.

We have surprisingly found that if crude petroleum containing salt water and gas is washed with water of lower salinity than the salt water already present, and then the mixture with increased water content is passed to a separator where water, crude petroleum and gas are separated, then a more efficient de-salting operation can take place than if the crude petroleum was washed after gas separation.

According to the invention there is provided a method for reducing the salt content of a crude petroleum present in a salt water/crude petroleum/gas mixture, which method comprises washing the salt water/crude petroleum/ gas mixture at a pressure above atmospheric with wash water of lower salinity than the water present in the salt water/crude petroleum/gas mixture, and then separating out at least some of the gas and some of the water from the crude petroleum.

By gas is meant any substance or compound which is in the gas phase at atmospheric pressure and the temperature of the separation. Normally the gases present in association with, or dissolved in, crude petroleum are methane, ethane, propane and butanes.

The washing of the salt water/crude petroleum/gas mixture can take place using any conventional washing technique. However as the mixture to be washed is under pressure then the wash water has to be added under pressure e.g. by means of a pump.

The separation of the water from the crude petroleum and gas preferably takes place in a three phase separator with simultaneous separation of gas, water and petroleum. The separator is preferably a high pressure separator, and the crude petroleum is then fed to a lower pressure gas separator to separate more gas and optionally more water. There can be a series of gas separators the last of which reduces to atmospheric pressure.

If the original salt water content of the crude petroleum is high e.g. about 30% by weight or higher, preferably some preliminary separation of salt water is carried out before addition of wash water, e.g. in a cartridge type coalescer. In off-shore locations some water separation and optionally some gas separation can take place at the well head, or other suitable off-shore site and the water wash can take place on-shore.

Preferably sufficient wash water is added so that the salinity of the water is below a specified value e.g. below 25 pounds per thousand barrels.

The amount of wash water required to give a final salt content and water content in the de-hydrated crude petroleum can depend on the salinity of the co-produced water, the volume of the co-produced water, and the salinity of the wash water.

For example where it is desired to achieve a final salt specification of S pounds per thousand barrels (ptb) and a water level after de-hydration of 0.05% vol (500 ppm) then 25S 25S y (b- )=x ( -a) 44 44 where y= ,Ó volume on crude petroleum of co duced water b= % salinity of co-produced water (NaCl weight equivalent) x= % volume on crude petroleum of wash water a=% salinity of wash water (NaCI weight equivalent).

In a typical case S = 25 ptb a=3.4 b=25 and approximately an equal volume of wash water to the volume of co-produced water is required to be added.

Demulsification additives are sometimes added to crude petroleum/salt water mixtures to reduce the amount of water in the crude oil and anti-corrosion additives are also normally added to protect the pipeline and other equipment. These additives can be added before simultaneously with, or after, the addition of the wash water.

A schematic flow diagram of a method according to the invention is shown in the accompanying drawing.

In the drawing a supply of salt water contaminated crude petroleum flows along pipe 1 and wash water from supply 2 flows through pump 3 into the salt water contaminated crude petroleum. Demulsifier and anticorrosion additives are added via metering pump 4. The mixture then passes to high pressure gas separator 5 where gas separates and is removed via outlet 6, water separates and is removed via outlet 7 and the crude petroleum passes out through outlet 8.

The crude petroleum still contaminated with salt water and containing dissolved gas passes to low pressure separator 9, where gas separates and is removed via outlet 10, salt water separates and is removed via outlet 11 and the crude petroleum stream free of dissolved gas and with salt content which is below the limit required is passed to storage facilities e.g.

Horton spheroids.

WHAT WE CLAIM IS: 1. A method for reducing the salt content of a crude petroleum present in a salt water/ crude petroleum/gas mixture, which method comprises washing the salt water/crude petroleum/gas mixture at a pressure above atmospheric with wash water of lower salinity than the water present in the salt water/crude petroleum/gas mixture and then separating out at least some of the gas and some of the water from the crude petroleum.

2. A method according to Claim 1 wherein some preliminary separation of salt water is carried out before addition of wash water.

3. A method according to Claim 2 wherein the preliminary separation is carried out in a cartridge-type coalescer.

4. A method according to any of the preceding claims wherein the separation of the water from the crude petroleum and gas takes place in stages at successively lower pressures.

5. A method according to any of the preceding claims wherein sufficient wash water is added so that the salinity of the water associated with the petroleum is reduced below 25 lb per 1000 barrels.

6. A method as hereinbefore described with reference to the drawing accompanying the Provisional Specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. In a typical case S = 25 ptb a=3.4 b=25 and approximately an equal volume of wash water to the volume of co-produced water is required to be added. Demulsification additives are sometimes added to crude petroleum/salt water mixtures to reduce the amount of water in the crude oil and anti-corrosion additives are also normally added to protect the pipeline and other equipment. These additives can be added before simultaneously with, or after, the addition of the wash water. A schematic flow diagram of a method according to the invention is shown in the accompanying drawing. In the drawing a supply of salt water contaminated crude petroleum flows along pipe 1 and wash water from supply 2 flows through pump 3 into the salt water contaminated crude petroleum. Demulsifier and anticorrosion additives are added via metering pump 4. The mixture then passes to high pressure gas separator 5 where gas separates and is removed via outlet 6, water separates and is removed via outlet 7 and the crude petroleum passes out through outlet 8. The crude petroleum still contaminated with salt water and containing dissolved gas passes to low pressure separator 9, where gas separates and is removed via outlet 10, salt water separates and is removed via outlet 11 and the crude petroleum stream free of dissolved gas and with salt content which is below the limit required is passed to storage facilities e.g. Horton spheroids. WHAT WE CLAIM IS:

1. A method for reducing the salt content of a crude petroleum present in a salt water/ crude petroleum/gas mixture, which method comprises washing the salt water/crude petroleum/gas mixture at a pressure above atmospheric with wash water of lower salinity than the water present in the salt water/crude petroleum/gas mixture and then separating out at least some of the gas and some of the water from the crude petroleum.

2. A method according to Claim 1 wherein some preliminary separation of salt water is carried out before addition of wash water.

3. A method according to Claim 2 wherein the preliminary separation is carried out in a cartridge-type coalescer.

4. A method according to any of the preceding claims wherein the separation of the water from the crude petroleum and gas takes place in stages at successively lower pressures.

5. A method according to any of the preceding claims wherein sufficient wash water is added so that the salinity of the water associated with the petroleum is reduced below 25 lb per 1000 barrels.

6. A method as hereinbefore described with reference to the drawing accompanying the Provisional Specification.