Breaking new boundaries is essential to stay ahead in the subsea equipment business and a pioneering project in the US Gulf is doing just that by notching up a number of technology firsts.
BP's Thunder Horse project has required development of high pressure and high temperature subsea trees and wellheads that have taken strides forward in the evolution of subsea hardware.
For suppliers, it's a substantial achievement to qualify equipment for this project which will be installed in water more than a mile deep. Apart from withstanding incredible pressure, reservoir characteristics require subsea hardware being supplied by FMC to withstand incredible temperatures - greater than that previously encountered on any subsea project. Wellheads on Thunder Horse have been built to withstand 15,000 psi of pressure and 350?F (176?C) - at least 100?F (37.78?C) more than the nearest alternative tree design.
Four years of research and development, and US $11 million, has been put into perfecting the trees. Along the way, 57 different equipment qualification tests had to be carried out.
Each 5-in. by 2-in. 15,000 psi tree weighs 50 tons. It is interesting to note that a rival 4-in. by 2-in. tree designed for 10,000 psi service was built weighing 63 tons. Thunder Horse trees have the advantage that they can be lifted, handled and installed as a single unit, whereas other trees have required transport in smaller components due to their size and weight, and needed offshore assembly, at considerable cost to clients.
Due to the extensive design and engineering on the trees, this same technology is to be deployed on at least two other Shell-operated projects in the US Gulf which are scheduled onstream before Thunder Horse.
Brian Skeels, manager of FMC subsea systems technology, nominated development of the Thunder Horse 15,000 psi tree for an internal prize - the FMC Technologies Technology award.
"The 15k HP/HT system has become the most technically advanced system in the subsea oil and gas market," Skeels stated. "The last 2 years have been the most extraordinary where almost every technology discipline and skilled trade in Houston has been involved, including material science, advanced control system hydraulics, thermal finite element analysis techniques, dynamic loading and thermal expansion pipe analysis, and reliability engineering."
One of the many Thunder Horse achievements was development of Novolastic HT, a silicone- based rubber insulation to isolate wellbore fluids at reservoir temperature from congealing at surface when exposed to sea temperatures of only 40?F (4.4?C).
"The real marvel of Novolastic is that it also is the only insulation on the market that can withstand the higher temperatures associated with HP/HT systems. Novolastic is capable of withstanding temperatures up to 350?F and resist the crushing water depth pressures up to 10,000 ft (3,050 m). The next best solution currently on the market can only withstand 220-250?F," Skeels pointed out in his award nomination.
"The Thunder Horse 15k tree weighs enough to be shipped and handled offshore in a single unit, saving considerable time, effort and cost offshore. BP even recognized the effort and sent a complementary note to the design team highlighting their achievement."
Skeels noted a rival 5-in. by 2-in. 10k tree, was built weighing 63 tons. "Theirs was so heavy that it had to be shipped offshore in three pieces and reassembled there at considerable time and cost to the customer."
Materials scientists changed their approach for the hydraulic connections on the trees, too. Because of the high reservoir fluid temperature, a higher grade stainless steel tubing was required for hydraulic connections between christmas tree hydraulic ports, due to the vulnerability of the steel to seawater corrosion at higher temperature.
Sub-suppliers to FMC, such as forging shops and mill shops, had to meet new manufacturing specifications for HP/HT raw materials.
Through finite element analysis, a new hydraulic connector was developed, which is 25% lighter with the same mechanical performance of a rival design. One was built to one quarter of actual scale for prototype and then for full-scale testing.
Apart from the trees and wellheads, there are over 100 miles (160 km) of pipeline, and flowlines between wellheads, manifolds and the surface facility on Thunder Horse.
Once fully operational, Thunder Horse equipment will operate at 270?F (132?C) but from a cold-start up and when dormant or shutdown, equipment will cool to the ambient sea temperature, 40?F, imposing tremendous thermal loadings on subsea components as they expand and contract. This will account for up to 4 ft (1.2 m) of expansion or contraction for every linear mile of those 100 miles (160 km) of pipe and flow lines.
Technicians working in a manifold and tie-ins group (Mantis) tailored the flowlines and jumpers for the field with sliding sled pipeline end terminations, floating pipe manifolds and jumper terminations that can "withstand torsional effects from the relative motions for the entire field," noted Skeels.
Metal to metal and non-elastomeric seals that could operate under repeated temperature load fluctuations have had to be designed by the contractor's new product group, PMC, ranging from 1/2-in. to 11-in. sizes.
Reliability engineering analysis was extensively used on the project, including statistical technology failure analysis - a technique taken from the aerospace and nuclear industries - to derive predictions for random and hardware failures.
In total 40 new products were qualified for Thunder Horse by FMC, including HP/HT gas valves and actuators in 5-in., 2-in. and 1/2-in. sizes. A valve actuator override was developed, plus a light, high-capacity 18 and 3/4 -in. connector rated for 15,000 psi and HT service. Other firsts were a 15,000 psi remotely operated vehicle (ROV) -installable tree cap; digital and analogue high temperature pressure sensors and an HP/HT choke.
By concentrating on value engineering, the contractor was able to cut the overall weight of the tree system by 40% compared with original design estimates.
Looking back on the history of subsea technology, Peter Kinnear, vice president of Energy Systems for FMC Technologies, speaking at OTC in May, noted that Shell Oil installed the first subsea completion in the Gulf of Mexico 42 years ago in a paltry 56 ft (17 m) of water. He said that installation, comprising a simple tree with four valves and bolt on connectors was effectively the start of the subsea energy production industry. He said it "...Originated a path that has extended to every ocean on the face of the earth and to water depths beyond imagination in the 1960s."
Another milestone was ExxonMobil's submerged production system (SPS), installed in the US Gulf in the mid-1970s which was a three-well diver-less subsea installation with pump-down tools, and underwater power connectors. It also featured multiplexed hydraulic controls and a remote flowline connector.
Shell's Cormorant field in the North Sea, co-developed with ExxonMobil, took elements of the SPS for its underwater manifold center. Norway's Snorre field developed by Saga Petroleum used many of the same features. "SPS was the testing ground for many of the standard subsea systems that the industry uses today," Kinnear told his OTC listeners.
The 1990s, Kinnear said, were "pivotal" for development of subsea technology, with big strides made in the development of modular systems, such as the Hinged Over Subsea Template, and deep records set by Petrobras on Roncador and Shell with Mensa.
More recently, the end of 2001 saw first oil from Girassol, developed by Total offshore Angola in Block 17, another deepwater production record with a huge subsea equipment spread. Others are set to follow, including the nearby Dalia development, also by Total.
Kinnear pointed to several key enabling technologies for exploiting hydrocarbons at greater depth. One is the ability to handle abnormally high temperature and pressure: "Designing subsea equipment capable of withstanding 15,000 psi working pressures and temperatures up to 350?F is a significant challenge," Kinnear suggested.
Providing reliable subsea pumping is part of the picture, another is applying onshore techniques for handling heavy crudes to the subsea environment. Development of reliable underwater power connectors is also part of the mix, and this appears to be have achieved with large stepouts from host facilities. He pointed to Total's subsea Otter development in the North Sea which used latest subsea pump technology to boost production while Unocal's Trident find plus Shell's Great White discovery in the US Gulf are in nearly 10,000 ft (3,050 m) water depth which will pose further subsea engineering challenges.
Those are the technical issues only. There are others, including the ongoing battle for greater production optimization, and higher recovery factors. At the same time life of fields costs still have to fall further, said Kinnear, to bring marginal fields into the commercial arena.