Norway’s Statoil has been the offshore industry’s biggest proponent of the concept for transferring the processing of oil and gas from platform topsides to the seabed for both brownfield and greenfield projects.

Once merely a vision, the concept of “subsea factories” is now close to reality as the various building blocks required for an all-encompassing system are being deployed on various fields around the world.

The need for a subsea factory solution has become increasingly obvious as the industry moves farther away from land into deeper waters and colder environments such as the Arctic. The ability to carry out subsea processing tasks such as single and multiphase hydrocarbon boosting (pumping), gas compression, separation (gas/liquid and liquid/liquid with produced water reinjection), and raw seawater injection brings with it plenty of challenges.

According to Statoil’s executive vice president of technology, Margareth Ovrum, the company is looking to apply the subsea factory concept, or elements of it, around the world, including the Gulf of Mexico, Brazil, Tanzania, and the Arctic. It also does not apply only to greenfield projects, as Statoil’s focus on improving reservoir recovery rates from its assets both offshore Norway and further afield means it intends to apply it equally to brownfield developments.

Ovrum, speaking in a press briefing at OTC on May 8, said, “I believe the subsea factory is the most interesting project in the oil and gas industry today.”

A key part of the seabed factory solution is subsea compression. In simple terms, the closer compression can be placed to a well, the more gas can be extracted.

Statoil is on schedule to apply it first on its Åsgard field offshore Norway, with the operator expecting seabed compression on the field to get underway in 2015 using the giant 1,800-tonne compression module, although on a smaller scale its Gullfaks South subsea compression project also could start up in 2015.

The Åsgard module is due to be installed 200 km(122 miles) offshore, and Ovrum pointed out that it is expected to enable the extraction of up to 280 MMboe of extra oil and gas from the field, where reservoir pressure is currently falling.
“Why do we need a subsea factory?” she said. “We are going longer, deeper, colder, in harsher environments. It will be impossible in some areas to build platforms, and subsea facilities could be the key to the success in these areas.”

Jannicke Nilsson, senior vice president, technology at Statoil, added that in the short term the company is focused on using subsea processing to help with increased oil recovery, while in the medium term it is looking to utilize the full subsea factory concept to produce oil and gas back to a host facility. That could involve greenfield developments transporting hydrocarbons back to infrastructure that may be up to 600 km (487 miles) away (for gas), 200 km (for oil), and 50 km (30 miles) for heavy oil.

In the longer term, Nilsson added, Statoil is looking to have subsea factory solutions that are able to act as production hubs, with total independence from surface facilities, and transport processed market-quality oil and gas directly to shore.

Key technology issues still being tackled include the large power requirements for long-distance subsea projects. “We need the power to be distributed and with high reliability,” said Ovrum. She added that other requirements include being able to remove much more of the liquids, like water, from the gas and needing to develop more technologies to clean and treat the water for reinjection. “We also need to work further on how to monitor the system,” she said.

Turning her attention to the Gulf of Mexico, Ovrum noted that the subsea factory solution could have several spin-off effects there. These could enable the doubling of the percentage of average oil recovery from its Paleogene fields, she claimed. Artificial lift solutions such as downhole pumps and subsea booster pumps were highlighted as key parts of the solution, with Statoil looking to apply them possibly by 2018 on the Logan field in the GoM, subject to further appraisal of that reservoir.

Other benefits of a subsea factory, said Ovrum, apart from increasing hydrocarbon recovery and productivity, include health and safety benefits such as reduced fire and explosion risks, chemical consumption, manned offshore operations, environmental “footprint,” and improved energy efficiency.

Contact the author, Mark Thomas, at mthomas@hartenergy.com.