Transferring the task of the initial processing of oil and gas from platform topsides to the seabed for both brownfield and greenfield projects has been one of the offshore industry’s greatest technological challenges. Once merely a vision, the concept of subsea factories – a phrase coined by Statoil, one of the biggest proponents of subsea processing solutions – is close to reality. Today, the various components required for an all-encompassing system are deployed with increasing confidence in long-term performance and reliability.

The need to have subsea processing options – essentially the ability to manipulate the wellstream between the wellhead and host facility – at their disposal is vital for oil and gas operators, especially those at the forefront of pioneering ultra-deepwater projects or remote and harsh environment developments such as the Arctic Circle.

There are currently four main types of subsea processing applications:

  • Single/multiphase hydrocarbon boosting (pumping);
  • Gas compression;
  • Separation systems (gas/liquid and liquid/liquid with produced water reinjection); and
  • Raw seawater injection. The main prerequisites and enablers for the above applications are:
  • Long-distance/high-voltage power;
  • Advanced process monitoring and control; and
  • Cost-efficient installation, maintenance, and retrieval.

Higher recovery rates

With the generally accepted thinking that wet tree developments with boosters can deliver between 5% and 20% higher recovery rates compared to dry tree developments, the commercial benefits can be very persuasive.

This applies to both new and existing projects, with companies like Statoil making it a key part of future plans to improve reservoir recovery rates from both brownfield and greenfield developments. Much of the company’s focus lately has been on seabed gas compression, the most recent subsea processing technology, which has not yet been implemented in any field worldwide. In simple terms, the closer that compression can be placed to a well, the more gas can be extracted.

Traditional topsides compressors have a low tolerance for liquid, resulting in two approaches to subsea compression:

  • Separating the gas so that a “traditional” compressor can be used; and
  • Building a liquid-tolerant or multiphase compressor.

The operator is planning to break first ground by using subsea gas compression for some of its domestic flagship North Sea projects such as ?sgard (expected to be the first to get underway in 2015), Gullfaks South (also possibly started in 2015), and Ormen Lange (to be started at a later stage in its producing life). The company also has at least 10 other projects that it is considering for the same potential application.

But subsea processing covers a much wider remit than just gas compression and for some areas is considered an enabling technology for new projects without which fields cannot be profitably developed.

New ways of applying subsea processing

New technology development continuously opens the door to new ways of applying subsea processing, according to Simon Davies, project manager of Technology at Statoil (which receives more than 50% of its production from subsea production systems via 500 operated subsea wells).

In the future there is likely to be even tighter integration of subsea processing building blocks used as part of a complete field development concept.

The industry’s vision of a subsea factory may drive the application of more sophisticated gas processing on the seabed (gas sweetening and gas dehydration). Reinjection of produced water for pressure support rather than disposal will bring more stringent requirements for produced water quality (effective subsea produced water treatment and monitoring).

Longer and more remote step-outs also are raising interest in developing local, potentially renewable power generation concepts, Davies said.

Pumping and compression technology will continue to evolve, he continued, while separation systems will also become more sophisticated, incorporating compact separation technologies and electrostatic coalescers. More compact wet gas compression units also will emerge to enable the development of small and medium-sized fields.

Fast-growing market

This is why a number of companies have been carefully positioning themselves to capture as much of this growing market as they can.

Toward year-end 2012, FMC Technologies’ Chairman and CEO John Gremp in the company’s 3Q 2012 results presentation said that bidding and tendering activity for subsea processing projects was set to shoot up over the course of 2013 and 2014. As many as eight projects were in the offing for this year, he said, with at least that number lined up for the following 12 months.

Rival contractor Cameron also said in November that it was linking up with Schlumberger to create the OneSubsea joint venture (JV). The JV’s stated aim to manufacture and develop products, systems, and services for the subsea market also enables it to specifically target the expanding subsea processing market.

Cameron will hold a 60% stake in the JV, with Schlumberger holding the remainder. The latter’s reservoir, well completions, subsea processing, and integration platform expertise will be a major boost to the services Cameron will be able to offer as manager of the JV for the forecasted 16 seabed processing projects over the next two years.

The overall trends indicate that the number of subsea processing projects going forward will continue to rise sharply. A recent Bernstein Research report showed global deepwater production has risen from less than 500,000 b/d 15 years ago to about 5.5 MMb/d in 2012. Another 4 MMb/d of deepwater production could be flowing by 2020.

Future trends

Around 200 deepwater subsea fields are expected to come onstream over the next four years, with more than 11,000 subsea wells forecasted to be in operation worldwide by the end of this decade. As subsea processing technologies continue to advance, the likely trends and focus areas are expected to revolve around the following:

  • Technology replication – reusing knowledge, designs, and qualified technology;
  • Continued qualification toward deeper waters, longer step-outs, and heavier or colder crudes;
  • Promotion of standardization of components, procedures, and qualification specifications; and
  • Greater processing efficiency (flow assurance). Bearing in mind that these processing advances also will be equally applicable to mature shallow-water areas, their increasing application worldwide is inevitable.

Acknowledgment

Excerpts have been included in this article from SPE paper 20619.