The Perdido team faced a tough decision. A conventional topsides design required a series of modules that would have to be fabricated onshore, then lifted onto the spar and integrated offshore, but what if the team could constrain the design enough that it could be built and lifted in one piece?
|“One of the remarkable things about the Perdido development is that the companies that have worked on this project have turned in record safety performances,” says Robert Paterson, vice president Upsteam Major Projects, Americas.|
They already knew that Perdido would be a wet tree DVA spar, and were convinced that a single-lift topsides would be safer to build and less expensive than a modular system. The trick was giving the smaller topsides all the capability it needed to produce the field.
|Kurt Shallenberger, Topsides lead|
That was unique. The more familiar way for engineers to work is to let the facility they’re designing grow to the size it needs to be. Early weight studies suggested that Perdido’s topsides needed to be several modules. Technical benchmarking studies showed that BP’s design for Horn Mountain had the best function-to-weight performance of any spar built so far, so with the assistance of BP, Chevron and Alliance Engineering, the Perdido design team evaluated Horn Mountain’s design and operating performance.
“That led us to the lightweight Perdido concept,” Shallenberger says. “We selected Alliance as the engineering contractor because of its previous experience with Horn Mountain.”
Built for safety
Health, Safety and Environmental (HSE) needs drove the design of Perdido’s topsides. One of noticeable features is the 2.5-bar blast wall that separates the crew quarters from the drilling and processing equipment, but Perdido also has the most aggressive fire suppression and gas monitoring systems of any offshore platform. It is a reflection of how the industry in general is maturing in terms of fire and explosion protection. Planning runs the gamut from how to prevent a release and ignition, to how to mitigate the impact if you do have a fire or explosion, and how best to evacuate the platform.
“Industry has learned a lot, particularly since the 1988 Piper Alpha fire in the North Sea,” Shallenberger says. “If there is a gas release, for example, we now have sophisticated models to help us understand where the gas will go. Perdido has more gas detection than any other platform, probably by a factor of five. If we were to detect gas, we can quickly depressure the whole facility and divert the gas to our flare system.”
The Perdido design team did extensive modeling of the onboard firefighting capability. Perdido’s twin 5,000 gpm firewater pumps and automatic foam system is the most extensive fire protection layout of any Shell platform in the Gulf of Mexico. One revolutionary feature is that the system is automatic. Rather than having a water deluge system and a supplemental foam system, both manually triggered, Perdido’s automatic fire suppression system covers the entire platform, including the heliport.
“Computer modeling also helped us determine, if there were an explosion, what kind of overpressure to expect at various points throughout the facility,” Shallenberger says. “Blast walls shield not only the crew quarters, but also the safety equipment, work areas and evacuation routes. There are no production offices in the process areas, and the Incident Command Center is adjacent to the control room for real-time feedback. We spent a lot of time in the screening process to make sure that in this compact space, our people are well protected.”
Integrating the subsea systems
Perdido’s subsea system, which includes separation and boosting, direct vertical access wells and tiebacks to satellite wells, is a first of its kind.
“Integrating those systems was one of the most complex things we’ve done on this project,” Shallenberger says. “From a topsides perspective, we are looking at recovering oil and gas from a collection of low-energy reservoirs.”
|Randall Hance, structural verification engineer, was on the spar site team in Finland.|
The low energy reservoirs demand low boarding pressures to be able to flow at reasonable rates. Gas flows to the surface against 460 psi, while oil is pumped from the seafloor against 160 psi at the surface. Elsewhere in the Gulf of Mexico, deepwater wells flow on their own. On another platform, production might come it at 1,600 psi, which is normally enough to move fluids through the export lines to sales. Since Perdido is so far from the nearest sales line and the reservoirs are low pressure to begin with, the export pressure from the spar is 3,200 psi.
“It takes a lot of horsepower to make that happen,” Shallenberger says. “It helps that the liquids and gas are separated on the seabed. On the topsides we separate the oil and water. The gas and oil are exported via two export pipelines, and the produced water is cleaned and discharged overboard. We also have a waterflood, but for that we use seawater.”
Steel and equipment for the Perdido topsides came from around the world. What designers called the box – the structure that was designed to fit the lifting capabilities of the Thailf SSCV – was built at the Kiewit yard in Ingleside, Texas, just across the bay from Corpus Christi. Ingleside is the same facility that completed the spar in 2008. The crew quarters were built at Delta Engineering on the Houston Ship Channel.
Working through storms
Katrina, the most expensive hurricane in U.S. history, made landfall in southeast Louisiana on August 29, 2005. Much of the Perdido team, then in the early stages of design and engineering, was displaced for six months. It was the first big storm to disrupt the project, but not the last.
“When Katrina wrecked the city and Shell’s offices in New Orleans, we moved the Perdido team to Houston,” Shallenberger says. “We began the front-end engineering and design (FEED) process while we were displaced. That was a big issue for our folks, traveling back and forth, fixing our homes on the weekends and coming back to Houston during the week.”
|The design of the topsides depended on the capacity of the heavy lift vessel that would be used to place it on the spar in a single lift. Heerema’s Thailf, named after a servant of Thor in Norse mythology, is the largest semi-submersible crane vessel in the world. Depending on the configuration of the load and angle of the lift, Thialf’s dual cranes can handle up to 14,200 metric tons.|
Three years later, when Hurricane Ike made a midnight surge into Galveston Bay and up the Houston Ship Channel, it passed right over the Delta Engineering (now Delcor USA) fabrication yard and Perdido’s almost-finished crew quarters. By early morning, much of Galveston was under water, 90 percent of Houston was without power and 100 miles of Texas beaches were gone.
“After our experience with Katrina, we were prepared to deal with Ike,” Shallenberger says. “We knew what problems the Delta yard was going to have and we responded right away. Workers were displaced. Most had damage to their homes and families to care for. Since the Delta yard itself was heavily damaged, workers were also concerned about their jobs. We stepped in very quickly to help Delta keep their contract labor employed.”
|Keith Smith, Transportation and Installation lead|
Shell responded with food, water and fuel. Shell’s emergency response team even brought in temporary housing and laundry facilities. That support continued for several weeks, until Delta and the rest of Houston got back on its feet. Fortunately, topsides construction at the Kiewit yard was far enough down the Texas coast that it was not affected by Hurricane Ike, and even the crew quarters survived the storm in relatively good shape.
“Perdido’s living quarters, which were in the yard at the time of the storm, were not heavily damaged,” Shallenberger recalls. “Two days before Ike made landfall, we calculated that if the storm surge came up too high, our quarters building would float off of its supports. We decided to pull the doors off the bottom floor so that if the water did rise, it would get in the lower floor and keep our building from floating. There would be wind and water damage, but we wouldn’t lose the whole thing.”
Perdido’s distance from its air and marine base in Galveston, more than 200 miles to the north, means that most service boats are 18 hours away, and even a helicopter transport takes at least 90 minutes. Shell, and many other operators in the Gulf of Mexico are using relatively large helicopters so they can evacuate and service their platforms efficiently.
These bigger helicopters, like the twin-engine Sikorsky S-92, can carry up to 19 passengers, but they need plenty of room and a sturdy landing space. Perdido’s heliport is large enough for two S-92s. It is built of aluminum, and equipped with advanced safety features to prevent fuel fires on the helipad.
|The topsides design team used extensive 3D modeling and the input from experienced operations staff to plan the location of equipment aboard the spar.|
In case a helicopter goes down nearby, most platforms have small, 6-person Zodiac style boats that can reach survivors quickly. With larger helicopters serving the platform, however, the topsides designers needed something bigger. Perdido now includes a 24-person, enclosed, fast-rescue craft.
Human factors and materials handling
As part of Perdido’s safe design, planners used 3D design tools to make things easier for people to operate, service, repair and move around on the platform. To advise Shell’s own safety specialists, the design team called in operators with extensive offshore experience and outside experts in Human Factors engineering.
“Every week for two to four hours, we would take a portion of the facility and walk through it in 3D,” Shallenberger recalls. “We wanted to understand where things should be: what elevation to put a valve, for example, or where to put a pump and how a person might work on it safely. We made frequent adjustments so that an operator servicing a piece of equipment would not be leaning over at an awkward angle or trying to lift something that was too heavy. We made sure the equipment was as accessible as possible and easy to maintain.”
|At the peak of activity, as many as 270 people per shift worked to complete the final hookup and commissioning of the Perdido spar. |
Photo Courtesy of Hornbeck Offshore Services.
His team studied Materials Handling in the same way. “We looked at all the equipment and determined how often someone might have to work on it. Some things you might not touch for a year, but other items, such as filters, might be replaced twice a month. We wanted those items within easy reach and the replacement parts easy to move. They can’t be too high or too low.”
If something an operator handles regularly weighs more than 50 pounds, for example, the topsides designers included room for a cart, dolly or small portable hoist. They also made sure that the cart or lifting system would have room to move around the platform to reach storage areas or outboard cranes.
Other aspects of Material Handling include structural engineering. If a 35,000-pound generator has to come out of it’s place in the middle of the platform, will the pathway out be strong enough to support it? Can it be moved to the edge of the deck at a point where cranes can reach it? Will overhead pipes and trays be in the way?
Production people were core members of the Human Factors and Material Handling reviews. Sometimes they would bring along the mechanic or production operator who performed a certain operation so they could explain to the designers and engineers just how the operation was done.
“I think we got most of it right,” Shallenberger says. “But it would have been hard without 3D modeling; it’s a critical design tool.”
Transportation and installation
Since the spar had to be towed to site in a horizontal configuration, the deck and quarters had to be integrated offshore. The topsides sailed from Kiewit’s Ingleside yard on March 8, 2009. The topsides lift was completed on March 13, and the living quarters were added three days later. At 9,773 short tons, the single-piece lift of the Perdido topsides was the heaviest ever in the U.S. Gulf of Mexico.
A model for ultra deepwater
The design of any deepwater project depends on the nature of the reservoirs, water depth, number of wells and a host of other factors. While no single platform can serve every need, the Perdido concept certainly adds new tools to the box.
Scott Chitwood, Topsides Structural lead
“This is a very repeatable design,” says Dale Snyder, Perdido project manager. “We have put a high degree of functionality into a smaller package than the industry has seen before. We and our JV partners are looking for ways to replicate that in future developments. I wouldn’t be surprised if the Perdido concept showed up in other places.”