Judy Maksoud, International Editor
Hurricanes Katrina and Rita taught the oil and gas industry some costly lessons. One of those lessons is that structures designed for operation in the Gulf of Mexico have to be able to contend with conditions that far exceed those previously considered “extreme.”
Dealing with extreme conditions is one of the selling points of the new Satellite Services Platform (SSP) vessel recently introduced by OPE Inc.
Tackling the waves
“In hurricane conditions, there are long, large waves,” explains Richard Haun, senior vice president of OPE and the vessel’s designer. “You want the buoyancy to be sufficient to accelerate the mass up out of the trough, but not to accelerate too rapidly. The SSP rides the wave vertically, but the accelerations are very low, so the vessel is extremely stable, and the risers are not being unduly stressed even in extreme conditions.”
An operator using an SSP would never have to move the facility off a field because of a 1,000-year hurricane, Haun says. “You would remove the crew, and you could increase freeboard by removing some of the crude storage using a shuttle tanker days in advance of a storm. As a result, you wouldn’t even get a splash on the deck.”
Gary Quenan, president of OPE, seconds Haun. “Our design has very efficient and very safe motions in normal operating conditions. In an extreme storm, there are more severe motions, but the SSP remains stable.”
Designing the SSP
The secret to the vessel system’s stability is its spherical hull. The SSP’s patented spherical hull design incorporates a round platform shape that presents a consistent “face” to winds and seas regardless of direction. The unique shape of the hull and center column was the starting point for the OPE design and is the feature that sets it apart in terms of appearance as well as performance.
The SSP-320 design can hold 1.25 MMbbl of oil and can produce 80,000 b/d.
“One of the things we wanted to achieve back when we began with a plain piece of paper was to have something analytically simple,” Haun says. “We wanted a simple shape with no square corners.”
The shape is important. When a structure’s shape causes fluid separation and vortices, there is some guesswork required to determine how the structure will act, Haun says. “It is difficult to match the guesswork to how the full-scale structure will perform in a real-world environment. Our strategy was to avoid all of that and not get ourselves into a situation where we did not have a predictable design.”
While the spherical shape is stable and consistent in the predictability of its motions, the center column ballast further improves the structure’s degree of stability.
“The SSP is stable, period - even when it’s empty,” Haun says. “The hull shape itself makes the pitch hydrostatically softer when the SSP is empty. We have a high degree of hydrostatic restoring moment, and that gives the system stability even when the column is up for shallow-water transit.”
The height-adjustable center column extends the extreme stability of the SSP because it adds stability like the keel on a sailboat, Haun explains. Also, the column is ballasted at its base for even greater improvement to the vessel motions.
Testing system performance
OPE recently tested the SSP at Marin’s facilities in the Netherlands. “Marin is one of the finest institutions in the world, and we tested the SSP there for that reason,” Haun says.
Test results demonstrated less than 4° of significant pitch and roll under Katrina-like metocean conditions.
OPE tested the SSP at Marin’s facilities in the Netherlands. Test results demonstrated less than 4º of significant pitch and roll under Katrina-like metocean conditions, OPE says.
In quartering seas and severe storms, a shipshaped vessel, by virtue of its shape, is at the mercy of wind and wave motions that do not negatively impact the SSP.
“When the SSP is empty, the natural pitch period is 30 seconds,” Haun explains. “Once you get to 30 seconds, you’re outside the wave frequency and swell and sitting pretty. It’s perfect,” he says. “To achieve those motions with the vessel empty is a huge achievement.”
OPE says the platform cannot be capsized.
From concept to construction
Though the SSP design is scalable, OPE plans to build a hull that is 320 ft (97.5 m) in diameter and can store approximately 1.25 MMbbl of oil because that size will be the most marketable, Quenan says.
“The market that is most fertile right now is the FPSO market. This design is an excellent solution for an FPSO application because you get more storage volume versus required steel with a spherical shape than you can with any of the competing designs,” Quenan says. “There are 150 FPSOs on the books to be built and deployed over the next five years.” The SSP-320, he says, could easily be used in place of any of them.
Detailed design is under way and should be completed in March 2008, Quenan says, noting that the company is in talks with some shipyards and is making plans for construction. “Most of the preliminary design work has been done; so the ‘design’ we’re talking about is actually a set of construction drawings,” he explains.
Meanwhile, OPE is actively marketing and promoting this design and is in talks with a number of potential customers.
One of the selling points of the SSP-320 is expected to be cost.
Savings on steel will be significant, Quenan says. “Based on construction, the weight of the SSP is about half the weight of a shipshaped production system of comparable storage capacity.”
The difference in steel weight alone could lower overall fabrication costs by tens of millions of dollars, says Haun.
The structural weight of the SSP-320 is 16,000 metric tons (17,637 tons). A comparable storage capacity tanker would weigh 27,000 metric tons (29,762 tons). “We estimate that the SSP will reduce newbuild costs by as much as 50%,” Haun says.
Construction is fairly simple because the segments that make up the hull are identical, and they can be welded along a clean line that can be inspected from either the inside or outside of the hull.
The spherical shape of the vessel’s hull consists of rectangular and trapezoidal pieces, Haun says. “One of the construction benefits is to begin with a flat plate. You put a girder segment and stiffeners on it and weld it out on the flat. When the sections are completed, they can be welded together. It is very, very repetitive, which makes construction simple.”
Newbuild hull construction time is estimated at no more than 18 months.
Installation represents additional savings. Unlike other floaters, the SSP does not require a dry dock to construct, which means it can be built in nearly any port in the world, equipped on shore, and dry or wet towed to the location with the center column either raised out of the water or lowered sufficiently to provide towing stability.
The company says that while its SSP-320 design is ideal for operations in the deepwater Gulf of Mexico, it has application worldwide.
There is no depth limitation to the design, Quenan says. Its water-depth limit is constrained only by current mooring technology.
“The SSP offers the oil and gas industry an exciting opportunity to significantly reduce capital costs and to increase performance in a wide range of applications,” Quenan says. “The bottom line is that this vessel is stable, it’s economical, and it’s safer.”
The SSP is also flexible. It can be built in diameters ranging from 60 ft (18 m) to 420 ft (128 m), and it can perform a broad range of functions.
The SSP can be used as an FPSO or FSO, control buoy, LNG unloading terminal, early production platform, minimal field facility, or as an FPSO with workover or drilling capabilities. The SSP is designed to support oil and gas processing facilities and can accommodate both dry tree and subsea wells.
For production purposes, Haun explains, it is easier to add subsea wells to the SSP than it is to add them to shipshaped FPSOs because the SSP does not require a limiting multi-pass swivel (turret).
It is also easy and inexpensive to redeploy, Haun says, because the platform topsides do not need to be voided. There is no need for deck removal or upending, which are necessary when redeploying a tension leg platform or spar.
Practice makes perfect
Haun, who spent 11 years developing the SSP, believes the design has benefited from the long evolution process that has brought it to its present state. “When you work on something long enough, you have the chance to continually review what you have done,” he says.
“We really don’t have anything else to change. It’s finished, and it works very well.”
