B.P. Introduces Low-Salt Water to Enhance Oil Extraction, as part of Shetlands oil-boom.

As part of an anticipated massive oil boom in the Sheltlands, along with a revamping of the Sullam Voe terminal (confirmed just last week), B.P. intends to use a desalination plant to reduce the salt content of seawater so that it can more effectively flush oil from the surfaces of the rock reservoirs that contain it. http://www.bp.com/extendedsectiongenericarticle.do?categoryId=9044064&contentId=7077181 If the process can increase the amount of oil recovered by another 4%, from a current average of 35%, this will mean a substantial increase in output across the industry. Applied to the Clair Ridge field, which is in the North Sea off the western Sheltand islands, it is thought that, over the lifetime of the well, 640 million barrels of crude oil might be recovered using untreated sea water, but that 42 million barrels, over and above this, could be made available using the low-salt water. The cost of the desalination plant is $120 million, which will add $3 to the cost of a barrel of oil.

Crude oil contains a wide range of molecules, many of which are charged or polar. In the B.P. research laboratories at Sunbury on Thames, in the south of England, it has been discovered that the oil molecules form chemical bridges with doubly charged cations, such as Ca²⁺ and Mg²⁺ that are present on the surfaces of clay particles in sandstone. At the normal salt concentrations in seawater (3,500 ppm), the oil molecules are compressed close to the mineral surface, so preventing access by free cations that are necessary to displace the Ca²⁺ and Mg²⁺ cations and thus free the oil from the surface. As the salt concentration is reduced, the thickness of the thin film of water between the oil molecules and the surface increases, through an effect known as “expansion of the electrical double layer”, and permits access of free cations from the seawater. This releases the oil molecules from the rock surface.

For the method to work, two criteria must pertain: (1) the total salinity of the water must be low enough to relax the electrical double layer compression, and (2) the dipositive cation concentration needs to be lower than that of the reservoir water. Together, these factors allow most of the oil to be released that is bound to the reservoir surface by this mechanism. B.P. uses water flooding to recover 60% of its oil, and it is predicted that the low-salt (LoSal®) method might increase production over the company’s holdings by 700 million barrels.

This latest development is part of a predicted new oil boom in the Shetland Sullom Voe oil terminal, for which £300 million ($480 million) worth of investment is expected.The manager of the terminal  confirmed only last week that the following projects were going ahead:
● a complete refurbishment of the plant and pipework.
● introduction of a major gas-cleaning plant.
● construction of a temporary two-storey office building at Sella Ness.
● final work on the Project Aurora gas plant.
● overhaul, by its owners, Fortum, of the power station.
● overhaul of 16 giant oil storage tanks.

While only 9.2 million tonnes of oil were produced by the terminal last year, over its lifetime it has handled one-third of the British offshore oil production. The Clair Ridge development (where the desalinised water is to be employed) is expected to be a major producer, with two new platforms. Oil will be brought through the existing pipe to Sullom Voe from the end of 2016, which could continue for another 25 years, still being in operation in the 2040s.