Level measurement and control strategies for subsea separators

Level monitoring instrumentation is an essential part of hydrocarbon processing facilities, and has, together with separator technology, been widely addressed over the last decade. Key is- sues are production capacity, product enhancement, and well-flow control. The reliability and accuracy of the level instrumentation, and its ability to monitor all the interface layers of the separator, includ- ing the thickness of the foam and the oil-water emulsion, are par- ticularly important when considering the level instrumentation as the main sensing element in the automatic control of the separator ves- sel. Lately, industry focus has been placed on optimal automatic control to improve the quality of the production output, and to mini- mize the use of expensive and environmentally undesirable separa- tion enhancing chemicals. Recent developments in hydrocarbon production include subsea separation stations, where the con- straints placed on the reliability and accuracy of the level instrumen- tation are especially demanding. This paper presents level interface monitoring developments based on electrical, ultrasonic, thermal, and nucleonic physical principles for three-phase hydrocarbon separators, and introduces the notion of tomometry, meaning multi- point cross-sectional metering aiming to acquire information on the cross-sectional flow-component distribution in the process vessel intended for control purposes. © 2001 SPIE and IS&T.