All Electrical Subsea System -Flexibility is Key to Enable Low Emission and Cost Efficient Field Developments

Abstract

Abstract Subsea Adjustable Speed Drives (ASD) have in recent years been qualified to TRL4. String testing with a subsea multiphase compressor brought the technology to TRL5. In subsea fields (e.g. new developments, upgrades to increase recovery, or brown field refurbishments), the electrical systems often have several main electrical consumers driving both fixed frequency and variable frequency motor loads. This paper summarizes a number of studies showing how the qualified electrical subsea power technology can be utilized – generally with simple engineering adjustments – to handle a wide variety of demands and field conditions. The electrical system is thereby greatly simplified, especially compared to classical long step out solutions. A first project evaluation presentedin this work, centers on the topic of combining a larger adjustable speed injection pump with a smaller fixed speed pump without the need for a subsea switchgear, or even worse two step-out cables. Another project case, examined to use a step-out cable to feed the adjustable speed pump, and use the same cable to power the pipeline heating system, during the phases the pump is turned-off. One of the projects later explored cost effective solutions to drive two smaller pumps instead, where the cost of two full size drive units would not be attractive. Finally, a project study examined how the qualified subsea switchgear and adjustable speed drive could be used where all or some of the power for the compression function would come from local floating wind turbines. In all these described cases engineering solutions are proposed that avoid the development of new technology. The flexible subsea power technology can be supplied from CO2 neutral power sources either locally generated or transmitted from shore. The use of subsea electrical power technology located on the seafloor enables a superior energy efficient production. Combined with flexibility to support a number of use cases it becomes a very powerful sustainable alternative.