The world’s first compact electrostatic coalescer has been given a clean bill of health after nearly two years in operation on the Glitne field operated by Statoil in the North Sea.
The full-scale CEC pilot at Glitne (arrowed) dwarfed by its conventional predecessor to the left.
Effective separation of contaminated formation water from oil is immensely demanding, particularly because the amount of water - usually in the form of emulsions - increases rapidly as reservoirs are depleted.
Separation has traditionally taken place in gravity separators and bulky electrostatic coalescers laced with a cocktail of demulsifying chemicals.
However, growing demands for cost-effective field development and rising environmental concerns have led to the development of a new generation of light, compact and environmentally acceptable devices.
In the mid-1990s, Statoil patented the idea behind a compact electrostatic coalescer (CEC) and concluded a licence agreement with Kvaerner Process Systems (KPS).
This covers further development and commercialisation of the device in association with the University of Southampton in the UK.
A joint industry project was later established, initially by Statoil and BP and later with Statoil, Chevron and Norsk Hydro, to assess and facilitate scale-up issues for platform use.
Basically, the CEC enhances separation by applying a high voltage alternating electric field to an emulsion. This coalesces and aggregates the entrained water droplets so that they readily settle out in a downstream separator.
Coalescence occurs quickly under turbulent flow conditions and minimises the need for emulsion-breaking chemicals.
It also leaves the oil with less than 0.3% water content, which is somewhat below the normal refinery requirement because of its salinity.
The world’s first CEC installation was on Glitne in late 2001. Several years later, this remains in perfect working order after keeping the water-in-oil content well below 0.3% while reducing the need for chemical additives.
This result is encouraging for wider implementation and operational longevity.
The CEC prototype was nominated for the ONS Innovation Award in 2002, and is widely recognised today as being state-of-the-art.