Shifting compression subsea - part one

There is no doubt that moving activities from topside to subsea will help operators increase efficiency, reduce energy use and improve performance, as well as eliminate many of the safety and both CAPEX and OPEX cost elements associated with manned production platforms. This shift to subsea technology also ties in with the general trend towards E&P in deeper and more challenging waters, where the benefits of subsea operations are even more substantial.

However, while such technologies clearly offer considerable opportunities to de-man and reduce carbon intensity, they also place extreme emphasis on robust engineering, reliability and remote operability.

Reliability: The beating heart of subsea success

Recognising the many advantages available from subsea production as well as the paramount need for robust and ultra-reliable performance, engineering and technology partnerships are emerging with advanced subsea solutions. A joint venture between Aker Solutions and MAN Energy Solutions, for instance, is supplying a modular system based around MAN Energy Solutions’ high-speed compressor technology. Initially developed some 30 years ago, HOFIM^® – High-Speed Oil-Free Integrated Motor-Compressor – machines have been in use by the gas transport and storage industries for decades. Totally sealed and oil-free, the system has steadily developed to extend its proven capabilities across a range of applications, including upstream O&G production and in extreme subsea environments.

By using seven-axes active magnetic bearings and a high-speed motor, a host of components – such as the gearbox, lube oil system, dry gas sealing, their instrumentation and valving – disappear, along with their associated reliability and maintenance concerns. With less things to go wrong there’s an almost inevitable improvement in system availability. The simple, single casing design not only reduces complexity though, the footprint of the compressor system shrinks by 60% and its weight by 30% when compared with conventional compressors. A high-speed variable frequency drive cooled by process gas also adds significant efficiency advantages when operating at part load and confers a low peak starting current. This is a potential concern for operators who need to avoid creating grid disturbances when starting under a heavy load.

With high reliability and very low servicing and maintenance requirements, the compressors - available across a power range of 3 to 18 MWe and discharge pressures of up to 303 bar (4395 psi) - are well suited for remote and unmanned operations, a critical capability for subsea success. And, if maintenance is required, the compressor module can be independently retrieved as the core HOFIM compressor unit is integrated into the overall subsea module architecture with only a few interfaces.

The latest generations of subsea equipment are standardised, simpler, smaller and with lower CAPEX and OPEX. This modular approach also helps to provide predictable quality, repeatable volume, accelerated delivery times, reduced manning and increased safety.

This is the first part of a two-part article. Part two is available to read here: https://www.oilfieldtechnology.com/special-reports/12012021/shifting-compression-subsea--part-two/.

Read the article online at: https://www.oilfieldtechnology.com/special-reports/11012021/shifting-compression-subsea/