SS on Implications of Subsea Processing power Distribution - Subsea Power Systems - a Key Enabler for Subsea Processing
Authors: Midttveit Steinar , Monsen Bjarne , Frydenlund Snorre , Stenevik Karl 
Published: July 2010

The paper provides an overview of and operating experiences with the subsea power supply systems for the Statoil fields utilizing high voltage power; Lufeng (seabed booster pumps), Troll (oil/water separation, water re-injection) and Tordis (separation, boosting, water re-injection). The paper gives a status on performance of the power system for these projects, and an overview of the most important " lessons learned??. The Tyrihans pump power supply system, which represents the world's longest step-out with topside VSDs and highest subsea motor power, is also briefly presented.

Future fields utilizing subsea processing at deeper waters and with longer tie-backs will require further development of power system technology and Statoil is undertaking several qualification programs for such applications. Status of Statoil's main ongoing qualification programs within HV power is given, including R&D and study activities. The overview includes status on all main power supply components such as motors, connectors, VSD, switchgear, transformers and cables/umbilicals within these projects.

The information provided gives a good overview of " state of the art?? of subsea HV power systems and components within Statoil, and can be useful to both manufacturers and end users of subsea power components.

Introduction

Since installation of the world's first subsea electrically driven seabed booster pumps on the Lufeng field in the South China Sea in 1997, the installed power used for subsea processing systems has increased substantially - and is expected to increase further in the years to come. Subsea processing systems include single and multiphase boosting, compression and separation, and power demand is far above what conventional subsea developments require. The majority of systems installed today are boosting applications and app. 35 machines have been installed on the seabed worldwide (not including spares/replacement motors). Accumulated installed shaft power since 1997 will pass 50 MW by 2010 and be close to 70 MW by 2011 (confirmed projects Jan 2010), ref figure 1. Although the activity has varied over the years, the trend towards increased subsea power consumption is very clear. Statoil has played a key role in this development and within 2010 more than 25 % of the installed subsea power and approximately 30 % of all motors will be on Statoil operated fields.

Cost effective and reliable power supply systems is a key element in the success of subsea processing systems. While development and optimization of the processes and machines (multiphase pumps, compressors) has had attention from the industry for decades, real focus on development of subsea power supply systems has only been present for the last 5-10 years.

This paper gives an overview of Statoil experiences with subsea power supply systems and also presents ongoing qualification activities within the area. Only experiences within subsea power for processing applications are included, experiences with control power, instrumentation, process etc. are not included.

Statoil's experiences with subsea processing is described in another paper presented at OTC 2010; paper No 20619; Experience to date and future opportunities for subsea processing in Statoil.