Power Grid in Sea Reaches for New Depths
23 July 2012
Offshore operators racing to extract more oil from under deep waters have a vision of one day running wells remotely from land, reducing the need for multibillion dollar offshore production platforms.
That will take lots of electric power, though, and while the companies don’t have technology to generate electricity underwater, they are developing new ways to get it there from shore or from generators on the ocean’s surface.
Siemens is working on subsea transmission equipment that could deliver 100 megawatts at a distance of more than 70 miles from a generation facility – a dramatic increase from the 3 to 4 megawatts maximum transmitted now through cables from platform generators to the deep-water wells below.
"A subsea power grid lets you power up all your appliances to manage your field, and will allow you to do so for multiple wells,” said Adil Toubia, CEO of the Oil & Gas Division of Siemens Energy.
While underwater electric cables have been around since the 1800s, the technology to plug and unplug equipment underwater, known as "wet connections,” is still evolving.
Hits market in 2014
Siemens hopes to bring its technology to the commercial market by 2014. It includes a seafloor grid of switches, control gear, and transformers along with equipment to process the hydrocarbons.
The big challenge is making it all work in the deep sea.
"It is a hostile environment – corrosive, dynamic and high pressured,” said Michael Webber, a professor of mechanical engineering at the University of Texas at Austin. "Any equipment on the seafloor will have to be able to survive those conditions, along with marine life chewing on it or mussels growing on it.”
It also must be repairable. "At 5,000 feet, it’s hard to send a mechanic down,” said Brad Beitler, vice president of technology for FMC Technologies. "You have to be able to pull the plug on it at that depth and disconnect it. All the things you put on the seabed have to be retrievable back to the surface.”
Companies are moving forward with underwater grids despite these challenges, motivated both by the steep costs of building and staffing offshore platforms and the high price oil brings once it’s produced.
Chevron subsea specialist Rick Kopps said having more power available on the seafloor could extend the life and productivity of wells by allowing the use of more powerful pumps and other equipment.
Could double output
Additional subsea power also could allow operators to move compressors, separators and other production equipment from surface platforms to the sea floor nearer the wells.
"Oil recovery from the next generation of deep-water wells is about 10 percent with current technology,” said Neil Holder, vice president of technology and head of subsea operations for Aker Solutions, a Norwegian subsea technology company. "With a subsea grid powering new compression and separation technology, you could double that to about 20 percent.”
Aker Solutions, which has its U.S. headquarters in Houston, is running a test project with Statoil on the west coast of Norway, to determine how an underwater grid could be used to power a deep-water natural gas compression system.
The system includes batteries, charged through transformers, to provide an uninterrupted electrical supply for an orderly shutdown in the case of a power failure onshore.
Siemens is banking on the major operators investing in subsea power grids as a way to make deep-water drilling more efficient.
"How quickly subsea power grids get deployed is a question of investment and how quickly oil companies want to spend on infrastructure versus what they have,” Toubia said.