Advanced Profile Gauge for Multiphase Systems

Schüller R.B.*, Halleraker M.** and Engebretsen B.***

*Agricultural University of Norway, P.O.Box 5036, 1432 Ås, Norway, reidar.schuller@inf.nlh.no

**Sentech AS, Trollåsveien 4, 1414 Trollåsen, Norway, morten@sentech.no

***Sentech AS, Trollåsveien 4, 1414 Trollåsen, Norway, bjorn@sentech.no

Abstract - A profile gauge, based on the measurement of capacitance of the sur- rounding medium, is presented. 40 sensors (electrodes) are positioned along a rod. Each sensor uses an oscillator working in the lower 20MHz range. The presence of the surrounding fluid causes a change in frequency depending on the dielectric property of the fluid. This change in frequency is transformed to a volume-averaged value of dielectric constant of the surrounding fluid. Contrary to "normal" types of dielectric measurement techniques the advanced profile gauge does not measure the capacitance between electrodes.

The probe has been tested in an atmospheric system at ambient temperature con- taining salt water, condensate from the Sleipner field and air. The advanced profile gauge was fitted to a transparent separator with internal diameter of 380mm. The positions of the interfaces could be visually observed, and observations showed that the separator normally had four distinct regions; gas at the top, a condensate layer, an emulsion layer and at the bottom a water phase.

The results show that the measuring system was able to detect the gas/condensate interface and the condensate/emulsion interface within ±20mm in all the tests. With regard to the emulsion/water interface, this was detected within ±20mm in all but four tests.

The accuracy is within ±10% in all the tests. At high levels, the accuracy is ±5%. The reason for this is that values are predicted within ±20mm whatever the position of the interface.

Keywords: capacitance, oscillator, interface, separator