The first subsea gas compression system went online to enhance recovery from the Åsgard Field in the Norwegian Sea, Statoil ASA said Sept. 17.

Aker Solutions delivered the unique subsea compressors. Statoil in December 2010 awarded Aker a contract for the system, which consists of two 13,400-horsepower modules with identical sets of compressors, pumps, scrubbers and coolers fitted together in an 1,800-metric ton steel frame.

Placing the compressor on the seabed near the wellheads, rather than on a platform, improves recovery rates and reduces capital and operating costs. Subsea compression also leaves a smaller environmental footprint and is safer to operate than a conventional offshore platform, Aker said.

Compression will increase field production by some 306 million barrels of oil equivalent during the field’s productive life, Statoil added. It estimated ultimate recovery from Åsgard’s Midgard reservoir will increase from 67% to 87%, and from 59% to 84% from the related Mikkel reservoir, extending economic production to 2032.

The field, near the Arctic Circle, is among the northernmost offshore operations in the world in a region noted for stormy weather. Named for the capital of the gods in Norse mythology, Åsgard produces light crude oil, gas condensate and natural gas. It ranks among the largest developments on the northern Norwegian continental shelf, with 52 wells drilled through 16 seabed templates. Production started in 1999.

As a field gets older, natural reservoir pressure drops. In order to recover more oil and gas, compression is required. The closer to the well compression takes place, the more oil and gas can be recovered, Statoil said. Traditionally, compressors are installed on platforms or onshore, but Åsgard is more than 120 miles from shore and in some 970 feet of stormy water.

The compression project started in 2005 and a plan for development and operation was approved in 2012. An estimated 11 million man-hours have been spent from the start until completion, Statoil said. More than 40 new technologies have been developed and employed after prior testing and verification. Some of work took place at Statoil’s Kårstø, Norway, laboratory, the firm said. Overall, the compression project cost $2.3 billion.

Almost 50% of Statoil’s production is recovered through some 500 subsea wells. Statoil’s subsea expertise is essential to successful production efficiency improvement and increased oil recovery efforts, the firm said. It also has a major onshore presence in the Eagle Ford and Bakken unconventional plays.

“Subsea gas compression is the technology for the future, taking us a big step closer to our ambition of realizing a subsea processing plant,” said Margareth Øvrum, Statoil executive vice president for technology, drilling and projects.

When fully developed, subsea compression would allow current topside operations to be moved to the seafloor, allowing oil and gas to be recovered that would not otherwise be profitable.

Statoil Petroleum AS is the field operator with a 34.57% interest. Project partners and their interests are Petoro AS, 35.69%; Eni Norge AS 14.82%; Total E&P Norge AS 7.68%; and ExxonMobil Exploration and Production Norway AS. 7.24%

Offshore