Schematic illustration of zonal packers, the valve system and the location of single phase fibre optic flow meters in the Veslefrikk injection well A-11B.
Fibreoptic flow meters contain an array of extremely sensitive dynamic pressure sensors, which are interrogated using a surface-installed fibreoptic system.
Turbulent pipe flow generates coherent vortices which last long enough for their characteristic fluctuating pressures to be measured by wall-mounted fibreoptic pressure sensors.
Subsequent or real-time analysis of broadband signals coming from the pressure sensors provides accurate and consistent measurements of the bulk flow velocity or the individual flow rates of multiple phases.
Three single-phase flow meters combined with four hydraulically operated sliding sleeves were installed in June 2004 in the A-11B injection well on the Veslefrikk field operated by StatoilHydro in the North Sea.
Weatherford and WellDynamics supplied the meters and sliding sleeves respectively.
The well in question is special because it is subject to a reservoir recovery process known as water-alternating-gas (WAG) and contains a Diacs system which permits flow into several isolated reservoir zones to be controlled from the surface.
Both water and gas have periodically been injected through the well at daily rates of up to 7,800 cubic metres of water and 2.2 million scm of gas.
The flow meters help to control the desired amounts of water entering four middle Jurassic intervals, which are designed to improve oil recovery.
Some initial instabilities caused by acoustic noise from the downhole valves were dealt with by improving signal filtering in the software.
Since these modifications were performed, the downhole flow meters have provided reliable and on-line zone rates during both water and gas injection.
