Gannet E: The World’s Longest Subsea ESP
Mar 06, 2011
J.S. MacFarlane,
Shell UK Exploration and Production, SPE 38534
This paper was prepared for presentation at the 1997 Offshore Europe Conference held in Aberdeen Scotland, 9-12 September 1997. What follows is a 300 word abstract.
Abstract
Gannet E is a 20 API crude reservoir located 14km away from the Gannet A platform. Reservoir properties make artificial lift essential to produce the fluids back to the platform. During conceptual design an ESP was selected as the chosen option due to uncertainties surrounding reservoir and fluid characteristics. Subsea ESP’s are in operation elsewhere in the world (Petrobras Carapeba and Amoco Lihua) but these are in close proximity to the processing platform. The 14 km distance of the Gannet E field from the Gannet platform introduces some major technical challenges into this subsea ESP installation. ESP reliably has been poor in the past, and when combined with a subsea installation, this can become a major Opex burden. To avoid this, the Gannet E project established a project goal of achieving a two-year run life from the first pump.
ESP System Design
The first major system element is the power transmission system. The topsides variable speed drive unit needs to be matched electrically both to the transmission system, that is the subsea and downhole cable, including connectors, and to the ESP motor. High speed electronic switching devices, such as are found in static variable speed drives, will cause high frequency harmonics in their switching waveforms. If the power system is not properly designed, these can cause high voltage transients and possible voltage doubling in the cable, and high frequency torque components at the motor. The voltage effects can give rise to cable insulation breakdown as a function of time, and the torque effects can excite torsional vibrations in the long (40m) and torsionally flexible shafts of the motor/pump combination. In the case of the Gannet E the option chosen was to select a drive with known low harmonic content. This is the “Perfect Harmony” drive manufactured by ASIRobicon in Pittsburgh. Theoretical analysis, supported by field trials, has demonstrated the very low harmonic content of this drive/cable/motor combination. The field trials , using redundant downhole cable, have been carried out at 5,10 and 15 km cable length by Reda Pumps in Inverurie.
Projects
