Floating wind turbines are an interesting future source for offshore power generation as an alternative to gas-fired turbines. But the concept of windpowered water injection has never been tested before. A new DNV GL joint industry project plans to harness windpower to inject water into mature fields and enhance oil recovery. DNV GL has proposed a new concept called WIN WIN (WINd powered Water INjection) that will use floating wind turbines proven offshore technology to power water injection at offshore fields.
The Norwegian classification company invited companies this May to join its Joint Industry Project (JIP) to carry out an in-depth study of the concept. The technology integrates compressor and water treatment equipment into the substructure of a floating wind turbine,which is connected to a subsea well. For the first time, wind power would be used to inject water through a riser into the reservoir to help lift additional oil.
“We have received a fantastic response from the industry,” says Johan Sandberg, DNV GL Energy’s service line leader for offshore renewables and project sponsor for the initiative.”
The advantages of powering by windare many. Conventional water flooding offshore entails many systems that aretechnically complex, energy intensive andspace consuming. By moving the process to a wind turbine, WIN WIN would free up deck space, shorten the length of the power cable from the power source to the injection manifold, and reduce fuel costsand emissions from running gas turbines.If successful, the payback could be significant. Initial studies have shown the concept could reduce the cost of water injection and avoid costly topside modifications, all while reducing greenhouse gas emissions. The wind turbines are considered to be cost effective as platform-powered water injection even at short distances to the platform, mostly due to the high costs associated with refitting a platform with new gas turbines and water injection equipment, hiring heavy-lift vessels, and shutting down production for installation.
The base case for DNV GL’s pilot project is a 6 MW wind turbine that would power both an injection pump and a desalination system inside the foundation. At its simplest level, WIN WIN could pump raw seawater into the wells. Raw seawater has been injected successfully into fields before, such as the Tyrihans in the Norwegian Sea. But only a small part of existing fields tolerate raw seawater, says Sandberg. The ultimate goal is to incorporate treated water injection (e.g.low salinity water from a reverse osmosis process) into the riser that could target a much wider market.
The project is “very pioneering,”according to Sandberg. This would be the first time a stand-alone system would solely power a water injection system by wind. In the future, WIN WIN could even be used to power platforms that have a shortage of associated gas to fuel their turbines. A similar approach has been used to partly power the Beatrice platform in Scotland withoffshore wind turbines, albeit there it is also supplemented with a cable to shore.
“What we are doing here is more groundbreaking,” says Sandberg. “The WIN WIN project is about autonomous systems for water injection, and the other is about power toplatforms. There are many depletingfields with limited supplies of associated gas where they have to import gas or diesel from far away.”
The concept could be taken even one step further and incorporated into anautonomous subsea water injection system, like the one developed by Seabox. The Stavanger-basedcompany has created a subsea watertreatment system called SWIT (SubseaWater Intake and Treatment) that forthe first time purifies seawater at theseabed. Currently all water is treated onthe platform topsides.
“We have been in contact withDNV regarding WIN WIN,” saysTorbjørnHegdal, Seabox businessdevelopment manager. “There isa good match there and a very interesting application.”
Subsea Missing Link
Seabox’ proprietary technology works by disinfecting and removing particles via its electrochlorinator and HRG (hydroxyl radical generator) cells tuckedinto an 8 x 8 x 7 metre yellow box on the seafloor. The purified water can then beused for water flooding to improve oil recovery. Combined with membranes atthe seabed, SWIT can produce sulfate free water when scaling is an issue and low salinity water for enhanced oilrecovery through reverse osmosis to target initially non-movable oil in the reservoir.
“Currently only Heidrun (field offshoreNorway) removes sulfates, but many of the new fields will need to remove sulfates because of scaling problems”says Hegdal.
The company has just started a new JIP under the Norwegian Research Council’s DEMO 2000 program that will close the remaining technology gaps with SWIT combined with membranes. The goal isto deliver a fully integrated and qualified subsea low salinity facility that removes sulfate and salts from seawater at the seabed. A number of major internationaloil companies are participating in the JIP, set for completion mid-2015.
The SWIT technology is already fully qualified from previous DEMO 2000 projects and is currently being considered for use primarily in the North Sea and Gulf of Mexico markets. It is also considered the missing linkfor Statoil’s Subsea Factory concept,which moves all of the production processes from the platform topsides to the seabed.
SWIT’s advantage is that it can reduce energy costs by 20% and give full flexibility in planning the number of wells.The system would eliminate having to treat the water on the platform topsides– where there is limited space — and flow the water down again into the well. Shorter wells and no high-pressure pipelines reduce capital and operating costs to get water to the injection zone.
“Flexibility is the big value driver,”says Hegdal. “This puts the reservoir engineer in the driver’s seat.”
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