Profiler 'sees' through tank walls

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February 2002 Analytical Instrumentation & Environmental Monitoring

A version of the Tracerco Profiler had already proved its accuracy and reliability on-shore in refinery vessels for a combined total of 20 years when the technology was applied to separator measurement and control.

The instrument comprises sealed titanium dip-pipes installed within the separator through a single 6" or 4" flange. A narrow dip-pipe holds a vertical array of low energy radiation emitters. A typical system will have two parallel dip-pipes, each holding a detector of up to 48 Geiger Muller tubes. Combined, they can give a 96-point measuring system with a minimum vertical pitch of 28 mm.

Each emitter transmits radiation through the fluid within the separator to be picked up by the detector. Oil, water, sand, foam and emulsion have different densities, they will attenuate the signal passing through them by different amounts. The density registered by each tube is transmitted to a signal processing unit housed in the dome, above the dip-pipes.

Figure 1

The information is converted into serial data and sent via fibre-optic cable to the plant computer. On the screen the fluid density at each 28 mm channel is depicted in realtime. For the first time ever one can see a complete profile of the distribution of fluids within the separator:

* The interface between water and oil or oil and gas.

* The quality of the separation.

* The extent of foam build up.

* The total liquid position.

* The level of sand build-up.

Figure 2

The BP Forties field

In 1999, the Tracerco Profiler newly installed on a BP production platform in the Forties field detected a considerable build-up of sand within a separator. The operators were unaware of the sand and had attributed poor production rates to reservoir conditions. The thin oil phase made control difficult and good separation hard to achieve without water carry-over.

To remove the sand, the operators began to jet wash the separator. The overall effect was to reduce environmental risk, optimise assets and save on chemicals in the separator.

With the aid of readings from the Profiler, the operators monitored the effectiveness of chemicals added to control foaming and emulsion. Wastage was reduced. The separator was brought under perfect control. With residence time up to target levels, rates of production were optimised. The risk of carry-over was eliminated.

Whilst this was taking effect, a band of emulsion between the oil and water phase and foam on top of the water was observed.

Since installation two years ago, BP has carried out no maintenance on the system. The Tracerco Profiler is suitable for use on floating production facilities.

Tracerco Africa

(011) 706 2592

[email protected]

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Analytical Instrumentation & Environmental Monitoring

Profiler 'sees' through tank walls

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