Safe and continuous metering of the water level in horizontal downhole separators is essential to control the separation process and the water injection pump. A new level metering system, in which both the meter and the electronics are placed downhole, is being development by the Industrial Instrumentation Department at Christian Michelsen Research (CMR). The system is based on small, compact, ultrasound sensors.
CMR has been allocated a Demo 2000 project to develop a test prototype of the downhole level meter, jointly with Norsk Hydro and Kværner Oilfield Products. Last autumn (TU14/99) Teknisk Ukeblad described a new concept for downhole separation of water in horizontal wells, where the separated water is re-injected into the formation with the aid of a downhole pump. The oil is produced to the surface. The concept has been developed by Norsk Hydro and Kværner Oilfield Products.
“The prototype level system will be tested this summer in a horizontal test separator at Norsk Hydro’s research centre at Porsgrunn,” says the programme manager for process metering at CMR, Ronny Albrechtsen. “A full-scale version will be built when the test results are available in the autumn.”
The level metering system is specially designed to be able to meter the water level in downhole separation of water. The sensors are designed to withstand pressures of up to 700 bar and temperatures up to 150 degrees Celsius. One or more sensors are used as both transmitters and receivers.
The system sends ultrasound pulses through the fluid phase and registers the echoes that are reflected from the oil-water transition. On the basis of the registered measurements, the water level is determined with the aid of an advanced signal processing system.
Due to the limited space down in the well, the metering system is designed as compactly as possible. The sensors are placed near the fluid outlet in the separator.
There are many advantages in separating water from the oil down in the well instead of using separators on the production platform: it is simpler to perform the separation down in the well before emulsions are formed, and the need for separation equipment and water treatment on the platform is reduced, since the water is not transported to the surface.
There are also environmental gains, in the form of reduced discharges of polluted water and less use of anti-corrosives and additives in the production tubes.
Demo 2000 is a programme for project-oriented technology development in the petroleum sector. The programme is designed to contribute to long-term competitiveness and profitable development of the resources on the Norwegian shelf, and to bring new industrial products to the global offshore market.