Tapping small fields and coming up with economic early production system solutions offers engineers an interesting challenge. Elaine Maslin reports.
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Amplus’ VPU. Image from Amplus. |
There are some 210 “small pools” on the UK Continental Shelf, containing less than 15 MMboe each, but more than 1.5 billion boe in total.
The challenge remains to produce technologies that can economically produce these pools, which largely remain undeveloped due to their distance from existing infrastructure, reservoir complexity or lack of commerciality.
And engineers continue to offer ideas, from innovative subsea power production and controls systems (OE: December 2015), to small scale production facilities. OE looked at a number of unmanned production buoy type facility concept back in May 2014 and then again in January 2015.
During Subsea Expo, in Aberdeen this February, Crondall Energy, a floating production-focused engineering consultancy, and small-scale, dynamically positioned (DP) floating production vessel designer Amplus Energy Services put forward their concepts.
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*includes process skids and disconnectable turret system |
Amplus
Amplus’ concept is its versatile production unit (VPU), based on a DP vessel, which could be used as an early production system or a marginal field development option.
DP FPSOs are not unheard of, points out Amplus co-founder and Managing Director Ian Herd, during Subsea Expo. The Seillean was a DP FPSO used in the UK North Sea in the 1980s, developed by BP as a single well oil production (SWOPS) facility, before redeploying to Brazil in the late 1990s. The Helix Producer was a converted ice class train ferry, with DP, which was used to redevelop the hurricane damaged Phoenix (formerly Typhoon) field in 2010. ConocoPhillips also used the Munin FPSO, with DP, on the Xijiang field before it moved to the Huizhou field for CACT, Herd says.
“The advantage is that there’s no mooring,” Herd says. “We can turn up, and all the client needs to do is wet store the risers. We pick up the risers ourselves with a disconnectable turret and start production. On a conventional FPSO you need tugs for the moorings, survey vessels, heavy lift vessels, subsea construction vessels for the risers, etc. We do away with about 90% of that.” Doing away with mooring requirements reduces about US$25 million costs, he estimates.
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Crondall’s design, cross-section. Image from Crondall. |
For marginal fields, it could be used as an early production system to get cash flow started, or a late life field solution, Herd says. “We thought the main interest would be for small pools, small reserves in the North Sea, but actually we are getting more and more enquiries for early production in places like Angola and Ghana, to give the operator more reservoir knowledge before they decide on a permanent facility.”
The VPU concept is modular, so that it can be easily adapted to each field, and based on a previous hull design for the Orelia concept, with 30,000 b/d production capacity, potential for gas compression, produced water treatment with discharge to sea and produced gas or crude to be used for fuel. The process equipment would be from NOV, and the turret from FES.
Onboard power would be about 24MW, to handle anything like electrical submersible pumps, etc., and a stock tank heating system for handling waxy or heavy crudes. According to Amplus’ modeling of its design, the vessel could remain on station through hurricane force sea conditions and still only use about 35% of its installed power.
“If the client ever wants extra equipment onboard, we can disconnect in four hours, head back to port, add the equipment, then head out again, reconnect via the moon pool using an ROV in three hours and be on production again,” Herd says. “In an emergency, it could disconnect in 30 seconds.”
Two versions of the VPU, VPU112 and VPU200, have been set out (see table). To get one built would take two years, Herd says. There are three yards in Norway, Germany and the Netherlands that have already been identified with availability. The firm is in discussions about the design with three clients at the moment, Herd said in February.
Late 2015, Amplus struck a deal to work with Technip to offer the VPU solution, with Technip offering its project management, engineering and subsea products and Amplus supplying the vessel. As part of the partnership, Technip is looking to develop risers and umbilicals suited to this type of deployment – i.e. lower cost than might be used on a longer term field development, Herd says.
Crondall Energy
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The versatile production unit (VPU). Image from Amplus. |
Meanwhile, Winchester, UK-based Crondall Energy has designed a compact, remotely operated, multi-field, floating production system. The idea is a low cost development solution to fill the gap between subsea tiebacks and full facility floaters, said Ramon Kunkeler, project manager, Crondall, at Subsea Expo.
The design is based on a single column hull structure and integrated, buoyant “deck box,” with a ballast system using water and a high-density ballast. It would have compact process, separation, compression technologies, and use where possible low maintenance materials, such as fiber reinforced plastic. This would be mainly for piping, for instance for the fire water system, replacing steel components, which reduces the need for coating and maintenance, as well as reducing weight, Kunkeler says.
One system has been designed, for a specific application and environment, with 25,000 b/d capacity with a small amount of associated gas. The process deck has a 42m diameter. The total installed height of the floater is 58m with a 28m diameter column. The total installed weight is approximately 15,000-ton with sufficient capacity to increase the payload allowing more process equipment.
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Crondall’s concept. Image from Crondall. |
But, it could be scalable, making it smaller or larger depending on production capacity requirements, level of associated gas, the environment it would be in, etc., Kunkeler says.
The mooring system would use existing turret mooring technology with diverless installation, similar to existing disconnectable turrets. Production rates would be for ~10-25,000 b/d fields with 20 MMboe, possibly 30 MMboe.
Kunkeler sees the estimated $250 million, redeployable concept (not including risers and wells) as a 3-5 year development option for small fields. “It’s easy to build and install and to redeploy. It can be a standalone solution filling the gap between subsea tiebacks and full floaters. It’s flexible and scaleable and with low cost design driver,” he says.
The aim has been to make it easy to fabricate, at any yard globally, which means the hull is compact with a low draft at under 5m. The deck then floats and can be positioned just using tugs, removing the need for heavy lift vessels. “It is low opex as it’s a NUI (normally unmanned installation),” Kunkeler says, “with high functionality, process intensification, operational efficiency, and minimal motions,” because of the hull shape, maximizing process uptime.
However, to keep the size down, it doesn’t have any storage, which means production will need to be offloaded to a leased FSO or pipeline.
The idea is for it to be used on small, standalone oil or gas developments, in varying environments and where water depth doesn’t permit fixed facilities, or in support of longer range complex tiebacks, Kunkeler says. This could be from small low gas oil ratio fields, where the gas is used for power generation, or small gas fields, where there is an export route, to longer subsea tiebacks to support power and controls or chemical injection.
The only problem is, despite the efforts to reduce costs, at $30/bbl, it’s still not that viable.
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