This article highlights that major offshore oil and gas projects may help North America reduce its dependence on the oil cartel. When members of the Organization of Petroleum Exporting Countries (OPEC) cut their production by 4 million barrels per day from March 1999 to March 2000, they tripled oil prices, from $11 to $33 per barrel. The combination of higher gasoline, diesel, and heating oil prices led President Clinton and Congress to pressure the OPEC countries to increase their production. Spar technology has been used for 25 years for loading buoys and storage vessels. The spar is a floating system, basically a cylinder on end that maintains its position with mooring lines sunk into the seabed. Many offshore oilfields are beyond the reach of underwater pipelines. This is an opportunity seized by SOFEC Inc. in Houston. Since 1972, the company, a subsidiary of the FMC Corp., has designed equipment to support floating production storage and offloading systems. These systems consist of a floating platform, basically a moored ship-shaped vessel, equipped to accept oil and gas from a drilling system on the sea bed.
When members of the Organization of Petroleum Exporting Countries cut their production by 4 million barrels per day from March 1999 to March 2000, they tripled oil prices, from $11 to $33 per barrel. The combination of higher gasoline, diesel, and heating oil prices led President Clinton and Congress to pressure the OPEC countries to increase their production.
Although nine OPEC countries agreed to boost production by 1.45 million barrels per day in late March, the public should not expect any relief soon, according to Energy Secretary Bill Richardson. He said that fuel prices would increase and probably would not peak until summer begins, even if the oil-producing countries increase their output.
Many people in government and industry believe that increased production of North American oil and gas is the most feasible alternative to dependence on foreign oil and its vagaries in price. “We have more than enough oil and gas resources in the Gulf of Mexico and off the East Coast of North America that can be developed to put our economy on a stronger footing, rather than waiting on the decision of foreign governments,” said Ken Leonard, senior manager upstream at the American Petroleum Institute in Washington. The API is a trade organization encompassing all phases of oil and gas exploration, production, processing, transportation, and marketing.
Increased North American natural gas production would help the United States shake its OPEC dependency. “Utilities are shifting to natural gas-fired power plants, particularly to power newly built, suburban housing, and this would reduce the need for heating oil,” said Leonard.
However, stepping up North American production is easier said than done, because large tracts of fuel-laden acreage have been put off-limits by environmental restrictions. “For example, there are an estimated 137 trillion cubic feet of natural gas in the Rocky Mountains, but only about 29 trillion cubic feet are available for exploration,” noted Leonard.
The API representative sees offshore production in North American waters as a bright spot, despite environmental limitations. “There are plenty of reserves in the Gulf of Mexico, and off eastern Canada, that are much less risky to explore, in a business sense, than the large reserves off western Africa, where political instability on the mainland increases risk.”
Leonard said the technology to develop offshore fields is readily available. This is borne out by three projects being developed at the opposite ends of North America: Chevron Corp.’s Genesis spar, located 150 miles south of New Orleans; the Sable Island Offshore Energy Project, off Nova Scotia; and the Terra Nova Floating Production Project, near St. John’s, Newfoundland. All incorporate some of the latest offshore engineering designs, and can serve as blueprints for future efforts.
The Genesis oil field is 150 miles south of New Orleans in the Gulf of Mexico, across Green Canyon blocks 160, 161, and 205. The field lies in the Viosca Knoll Carbonate Trend and contains known reserves of 160 million barrels of crude oil.
Developing the Genesis field began with a discovery well Chevron drilled in 1988 that foretold of the area’s vast petroleum wealth. Further drilling over the next few years confirmed the presence of oil and gas reserves, but the deepwater recovery technology of the day was considered too costly, risky, and complex to exploit the field.
By 1993, Chevron had assembled a multidisciplinary team to determine whether new production facility designs—the spar and the floating production system— could be applied to the Genesis field. Chevron conducted feasibility studies of both concepts in 1994 and by May 1995, chose the spar concept to meet the design, budget, and time considerations.
Chevron formed the Genesis Development Project as a joint venture with Exxon Co. and PetroFina Delaware Inc., Chevron owns 56.67 percent of the Genesis project, Exxon 38.38 percent, and PetroFina 4.95 percent. The cost of building the Genesis production spar and drilling its wells is projected at $750 million.
Building an Island
Spar technology has been used for 25 years for loading buoys and storage vessels. The spar is a floating system, basically a cylinder on end, that maintains its position with mooring lines sunk into the seabed. The spar is equipped with a deep draft hull whose center of buoyancy is above the center of gravity, making it more stable than other types of floating platforms. The spar’s operating crew moves it within the mooring lines to work each well.
Spars International Inc. of Houston installed the first offshore spar platform in the Gulf of Mexico in 1,930 feet of water in 1996 for Oryx and CNG Producing. This installation was used solely for completing the wells, cleaning out debris from drilling, and packing the wells, prior to extracting the oil.
The Genesis platform is the first spar facility large enough to support production as well as drilling, and incorporates new designs in the hull, the interface between the wells and the hull, and the drilling, export, and production risers.
The Genesis project is built around a cylindrical steel spar, measuring 122 feet in diameter and 705 feet in length, designed to support both drilling operations and production facilities. The upper portion of the cylinder consists of watertight compartments that can withstand hydrostatic pressure and keep the spar buoyant. The lower portion of the spar contains tanks that are filled with seawater to provide ballast and stabilize the platform.
Spars International was the general contractor for the Genesis project. This company is a joint venture equally owned by two Houston corporations, J. Ray McDermott Inc. and Aker Maritime Inc. Both companies design and construct offshore platforms. They formed Spars International in August 1995 to promote, contract, and manage spars for offshore deepwater oil and gas exploration. Today, both Aker Maritime and J. Ray McDermott offer the technology separately.
The inherent stability of spar platforms enables their builders to equip them with rigid production risers, which connect the wells on the surface with the seafloor. The spar’s slight motion and protected center well provide an ideal configuration for deepwater drilling. In addition, the spar’s design facilitates the storage of large volumes of oil at low marginal cost and the use of traditional shipyard/offshore construction techniques.
McDermott Engineering built the topside section of the Genesis spar at its facility in Amelia, La. McDermott used 5,150 tons of structural steel, 2,600 tons of production equipment, and 945 tons of interconnecting piping, electrical lines, and instrumentation to construct the topsides of the spar. The finished deck surface covers about 100,000 square feet in three levels apiece of 175 feet square.
The McDermott engineers fabricated the Genesis topsides as two separate units—the production deck and the drilling/utility deck. The latter deck was cut into two pieces, between truss rows 1 and 2, to facilitate its transport from Ingleside, Texas, to the Genesis field.
Similarly, across the Atlantic, Aker Rauma Offshore manufactured the Genesis hull in two halves at its Mantyluoto shipyard in Pori, Finland. The first hull section weighed 10,842 metric tons and was 376 feet long, while the second section weighed 15,861 tons and was 327 feet long. Dockwise N.V of Meer, Belgium, used its Transshelf heavy lift transport carrier to ferry each section to the Aker Gulf Marine shipyard in Corpus Christi, Texas, in two 24-day voyages, in December 1997 and February 1998. After the hull was assembled at the Corpus Christi yard, McDermott Engineering used its Derrick Barge 50 to install Genesis on site.
The installation began with the spar’s 14-point mooring system. Each mooring line consists of 250 feet of 5.25-inch-diameter anchor chain, 3,000 feet of 5.25-inch-diameter wire rope, and 1,150 feet of hull chain.
Each mooring line was driven into the seabed. First, the engineers attached a chain to the mooring piles approximately 60 feet below the pile head, and connected a coated steel rope to the chain. They then assembled the hammers to the piles before lowering them both into the sea. The hammers were equipped with a special lifting head to enlarge their lifting capacity to carry the heavy weight of the piles, 3,590 tons apiece. The piles were 235 feet long with an outside diameter of 8 feet.
A challenge to installing the Genesis mooring lines was the existing network of pipelines and equipment in the area. McDermott prevented any conflicts by laying the connected Genesis chain and mooring wire along predetermined routes. The mooring wires were outfitted for later retrieval.
Each mooring pile/hammer assembly was lowered and penetrated 100 to 110 feet into the seafloor by weight alone. The hammers drove the piles down to 220 feet. It took McDermott an average of less than one day to drive each pile.
Once the mooring system was completed, in August 1998, McDermott brought the Genesis hull into the oilfield. Engineers performed a staged free flooding to send approximately 178,000 tons of water ballast into the enormous hull to upend it.
Tugboats positioned the hull near the center of the mooring pattern. Crews working from a temporary work deck then attached the 14 mooring lines to the chain jacks. Once the chains were drawn into the chain jacks, they were pulled to impart needed tension, and 10,000 tons of permanent seawater ballast provided stability. In addition to the production deck, the topsides of the spar include east and west drilling/utility modules, workers’ quarters containing 110 bunks, and the drilling rig.
Engineers built a 58-square-foot center-well in the hull to house the Genesis spar’s production risers. The center-well can accommodate up to 20 production risers, one drilling riser, and two export pipeline risers. Each riser is approximately 2,650 feet long, spanning the wellheads on the seafloor to the topsides of the platform. The subsea wellheads and export riser bases are spaced 20 feet apart to form a circle 140 feet in diameter.
Integral buoyancy cans on each riser permit it to float independently of the spar’s hull. The risers are equipped with a special keel joint that lets the riser move in tandem with the spar without buckling.
The Genesis Spar’s drilling rig was leased from Nabors Offshore Corp. in Houston. The 20-year-old rig was originally designed to be used with conventional steel jacket, and was modified to meet U.S. Coast Guard firefighting, lifesaving, and spill-prevention regulations for its Genesis spar application.
“We also performed substantial structural modifications to adapt the rig to the Genesis spar,” said Thomas Marcotte, a mechanical engineer and facilities engineering advisor at Chevron. “For example, we had to modify the derrick and drill floor of the rig to permit the risers and buoyancy cans to pass through them, because at 96 inches in diameter, the cans are four to five times larger than conventional drilling tools.”
Chevron conducted flow tests after drilling that show a single well in the Genesis field can produce rates up to 8,300 barrels per day. The oil company used a semisubmersible mobile drilling rig to drill 20 development wells to an intermediate depth, ran one string of casing into each well, then cemented it. The Nabors rig finished drilling the wells from the spar.
The wells began producing in January 1999. Chevron expects production to exceed the spar’s design basis rates of 55,000 barrels of oil and 72 million cubic feet of natural gas per day later this year.
“Chevron uses typical oil and gas separation and dehydration techniques on the Genesis spar,” noted Marcotte. This involves sending raw well fluids, usually consisting of a mixture of crude oil, water, and natural gas, to gravity separation vessels and skimming the oil off the top. Water from the separator bottoms is subjected to chemical and heat treatment to remove more water from the oil. “We process the remaining water to reduce oil and grease down to about 10 parts per million, and then dispose of it overboard, in accordance with environmental regulations,” explained Marcotte.
Natural gas accounts for approximately 14 percent of the hydrocarbon mix produced at the Genesis field. The gas is run through towers packed with glycol to dehydrate it to 2 pounds of water vapor per million cubic feet of gas. “We use about eight percent of the gas to fuel the spar’s generators and compressors, and export the remainder for sale.”
After treatment, crude oil is piped through the 14-inch-diameter export line run through the spar’s center-well to export pipelines connected to a tie-in point at South Timbalir Block 301. Similarly, treated gas is pumped through a 10-inch export riser in the center-well to a gathering system operating at Ship Shoal 354.
Cooking With Gas
More than 20 years before the Genesis field was discovered, starting in the mid-1960s, petroleum companies uncovered significant deposits of natural gas in the porous sandstone rocks that lie beneath the Sable Island area, located from 160 to 300 kilometers off the eastern coast of Nova Scotia. Further exploration through the next two decades showed six fields suitable for development. They are named Thebaud, Venture, South Venture, North Triumph, Glenelg, and Alma. The six fields contain about 85 billion cubic meters of recoverable natural gas reserves.
Sable Offshore Energy Inc. was formed in 1997 by Mobil Oil Canada, Shell Canada Ltd., Imperial Oil Resources Ltd., Nova Scotia Resources Ltd., and Mosbach-er Operating Ltd. to develop the Sable Island fields. Faced with tight economic conditions and very complex reservoir structures, Sable adopted an “alliance approach” that integrated the expertise from seven groups which became known as the Facilities Alliance. The Alliance consisted of Agra Monenco/Brown & Root Joint Venture, Elsag Bailey, Allseas Canada Ltd., Kvaerner Oil & Gas Ltd., MM Industra/Brown & Root Joint Venture, BBA, and Saipem UK Ltd.
The overall project includes constructing offshore production platforms to extract natural gas and associated natural gas liquids, such as propane and butane, from the seabed. The platforms will collect these fuels, dehydrate them, and then transport them through an undersea pipeline to a gas plant near Country Harbor in Guysborough County, Nova Scotia.
The gas plant will separate natural gas from the liquids. The gas will be conditioned and delivered to pipelines in eastern Canada and the northeastern United States. The liquids then will be sent, via a gathering pipeline onshore, to the Point Tupper area in Richmond County, Nova Scotia. Further processing at Point Tupper will provide “finished” natural gas fuel for the Canadian and U.S. markets through a new pipeline built through Nova Scotia and New Brunswick to tie into the Maritimes & Northeast pipeline grid.
The Saipem 7000, a heavy-lift transport vessel, shipped all of the offshore equipment from Halifax to the Sable Island fields in three trips made in 1998 and 1999. The drilling vessel was built in Italy by Saipem, a member of the ENI Group, and measures 198 by 87 by 45 meters.
MM Industra and Brown & Root formed a joint venture in Dartmouth, Nova Scotia, to build the North Triumph platform in 1999 and install it in September of that year. The platform is located 35 kilometers south of Sable Island and stands in nearly 76 meters of water. The entire facility is 106.2 meters tall and weighs 1,580 metric tons. To date, two wells have been sunk from North Triumph to produce natural gas. The collected gas is processed by a glycol system to remove some water before sending it along 35 km of 12-inch pipe to the Thebaud Central Processing Platform.
Similarly, the Venture platform, also completed and installed in September 1999 by Kvaerner Oil & Gas of Tee-side, England, drills, collects, and partly dehydrates gas prior to shipping it 57 km through 18-inch pipe to Thebaud. The Venture platform measures 62.9 meters tall, stands in water over 22 meters deep, and weighs 2,476 tons. A total of 24 people can work aboard the platform.
Kvaerner Oil & Gas also built the Thebaud Central Processing Platform for the Sable Offshore Energy Project. This is the largest of the project’s platforms, standing 70.7 meters tall in 27 meters of water, weighing 5,615 metric tons, and sleeping a full crew of 40. Thebaud processes gas from Venture and North Triumph, removing remaining water. In addition, Thebaud is a drilling platform, drawing gas from its own wells, and dehydrating that by glycol absorption, along with the gas from North Triumph and Venture.
Allseas Canada installed the pipeline that links the Thebaud, North Triumph, and Venture fields as well as the pipeline running from the Thebaud Central Processing Platform to Betty’s Cove in Goldboro. The company used its 285-meter-long Solitaire vessel to lay 26-inch-diameter, 197-km-long main gathering pipeline from the shoreline to Thebaud from late June to late August 1999.
The Solitaire’s work was supported by the Trenchsetter, another vessel in Allseas Canada’s fleet that dug trenches with remotely controlled equipment. For example, the Trenchsetter dredged out pilings and recovered pipeline with remotely controlled equipment.
A sister vessel, the Lorelay, laid the 57-km-long, 18-inch-diameter pipeline, with 3-inch piggyback piping, that connected the Venture platform to the Thebaud plant in May and June. Once that was completed, Lore-lay’s crew laid a 35-km-long, 12-inch-diameter pipe, with 3-inch piggyback, to connect North Triumph to Thebaud, at about 3 km per day.
Thebaud’s processed gases are sent through 200 km of 26-inch-diameter pipe to the Goldboro Gas plant, built specifically to serve the Sable project. The liquids are separated through a set of large-diameter pipes, about 200 meters long, to slow their flow so that the natural gas liquids fall to the bottom of the pipe. The gas and liquids are then fed separately deeper into the gas plant. As much as 14.4 million cubic feet of natural gas will be processed each day for delivery via the Maritimes & Northeast Pipeline.
Natural gas liquids are transported through underground pipeline to the fractionation plant at Point Tupper. There, the liquids are separated into propane, butane, and condensate before being shipped by train, truck, or boat.
There are plans to develop a total of 28 wells at the six Sable Offshore Energy Project gas fields, with one platform at each field. The members of the Sable project plan to construct satellite platforms at South Venture, Glenelg, and Alma from 2004 to 2007.
The new platforms will consist of unmanned wellhead and production facilities, each equipped with emergency living quarters and a helicopter landing deck. The Thebaud platform will continue to provide the central gather, dehydrating, and compression for the gas from the satellite platforms. The gas, condensate, and water generated from the satellite platforms move through a system of buried, undersea pipelines to Thebaud. The alliance will establish a 200-meter, no-anchor zone around the subsea gathering lines. The entire project is expected to produce natural gas until at least the year 2025.
Many offshore oilfields are beyond the reach of underwater pipelines. This is an opportunity seized by SOFEC Inc. in Houston. Since 1972, the company, a subsidiary of the FMC Corp., has designed equipment to support floating production storage and offloading systems, or FPSOs. These systems consist of a floating platform, basically a moored ship-shaped vessel, equipped to accept oil and gas from a drilling system on the seabed. The vessels remain on-station for years, processing, storing, and offloading crude oil to tankers that carry it to land.
Floating production systems are used in locations whose remoteness from offshore infrastructure or harsh climate makes conventional fixed platforms uneconomical. “For example, we are supplying equipment for a floating production system being built off the coast of Vietnam that is only 43 meters deep but miles away from existing oil pipelines,” said Ron Mack, a civil engineer and sales manager for Canada at SOFEC.
A critical subsystem of a storage vessel is the mooring turret, an assembly that runs from above the deck through the keel. The stack-like structure connects the crude oil transfer lines, hydraulic and electrical power lines, and control lines between the subsea wells and the surface.
“The turret is moored to the seabed and is designed to remain stationary, while the FPSO itself ‘weather vanes’ a full 360 degrees to accommodate the variability of wave, wind, and current directions,” explained Miles Hobdy, a member of ASME and the lead mechanical engineer at SOFEC.
The latest mooring turret SOFEC designed will support the vessel being used to develop the Terra Nova oilfield near St. John’s, Newfoundland. The Terra Nova oilfield is 350 km east-southeast of St. John’s, in the Jeanne d’Arc basin of the Grand Banks. The water in this area is about 95 meters deep.
The Terra Nova field is being developed by a consortium that includes Petro Canada, Mobil Oil Canada Properties, Husky Oil Operations Ltd., Norsk Hydro Canada Oil & Gas, Murphy Oil Co. Ltd., Mosbacher Operating Ltd., and Chevron Canada Resources. The owners believe there are approximately 370 million barrels of recoverable crude oil in the Terra Nova field. By producing 115,000 barrels of oil per day beginning in early 2001, its developers expect Terra Nova to be active until the year 2014.
The storage vessel at Terra Nova will produce and store crude oil until it can be transferred to a tanker that will carry it to land for refining. The facility also will inject seawater, and reinject some natural gas produced onsite, into the subsea wells to aid crude oil recovery.
Climatic considerations convinced the Terra Nova consortium to use the vessel. The waters off Newfoundland often have icebergs that can damage an offshore platform. The Terra Nova group decided to use an offshore production system that could be moved out of the way.
However, the legendary fogs of the Newfoundland coast mean that there’s a very remote possibility that a berg could slip through the iceberg management system and be close to the vessel before the crew is alerted. The situation would leave little time to move.
“We had to design a mooring turret that could be disconnected from the undersea buoy—connected in turn to the subsea wells—in 15 minutes, when an iceberg is suddenly seen as the fog lifts,” said Mack. The process usually takes four hours.
The SOPEC engineers used several computer-aided design tools to develop the quick-disconnecting mooring turret. They included MathCAD from MathSoft of Cambridge, Mass., AutoCAD from AutoCAD of San Francisco, AutoPlant from Rebis of Walnut Creek, Calif., and StruCAD made by Zentech of Houston. “We performed a lot of structural analysis using ANSYS software, and built our largest ANSYS model to date for this project, because the turret is basically a shaft 12 meters in diameter, 30 meters high,” said Hobdy. SOFEC designers performed hydrodynamics analysis for the mooring turret, using software written for the purpose.
Once the computer analysis was finished, 1/44- and 1/60-scale physical models of the vessel were built. These models were tested against winds, waves, and currents in wave basins operated by the Canadian Institute for Marine Dynamics in St. John’s and by Marintek in Trondheim, Norway. SOFEC used the computer analysis and wave basin test results to obtain information needed to design the various turret and mooring components.
“We broke new ground welding HY 80 and HY 100, which are the high yield steel alloys used to construct submarine hulls, when designing and fabricating the buoy/turret structural connector assembly,” said Hobdy. Typically, plates of these steels are 2 inches thick in submarine applications, but SOFEC joined pieces that were 8 to 10 inches thick. SOFEC also commissioned a mammoth chain made of 7-inch-thick bar stock to retrieve the undersea buoy and reconnect it to the turret. Each of the chain’s 96 links weighs about one-half metric ton, and can handle a pulling load of 2,600 metric tons.
The final connection between the submerged buoy and the turret is accomplished with a device called the connector/tensioner. The connector latches onto a mating hub installed on the buoy, and a large, dual-acting hydraulic cylinder acts as a tensioning device. The buoy is then hydraulically preloaded to the turret with a 7,700-metric-ton preload. This large preload is applied to minimize the effects of fatigue loading.
Daewoo of Seoul, Korea, is installing the mooring turret in the Terra Nova vessel, which the company is building at its shipyard in Okpo, Korea. Final hookup and commissioning of the vessel are scheduled for completion this year in Newfoundland, and it should be installed at Terra Nova in February or March of 2001.
The key turret component that allows fluids, electrical power, and control signals to pass between the stationary turret and the “weather vaning” vessel is called the swivel stack. One swivel will be used to test a well’s production, three swivels transport crude oil from the wells, and one swivel each will pass seawater to extinguish fires, to flare excess gas, and to inject gas and water into the wells to encourage crude oil production. The remaining swivels, in turn, provide nine paths for optic fibers and 72 control signal paths, and transmit electrical power to the equipment.