Some of the largest natural gas projects in the world currently are being developed offshore Western Australia, where operators are pushing the envelope with floating LNG (FLNG) vessels and subsea systems built to feed those facilities. Subsea technology is evolving rapidly to meet the long-term demands for producing and delivering that gas.

“When you look at Australia, everybody has this perception that it is all sandy beaches, flat calm water and everything is nice and easy. However, there are significant challenges in dealing with Australia because many of these subsea fields are long distances offshore. There is a very long cyclone season like the hurricane season in the U.S. That cyclone season is massively demanding,” said Mike Robinson, manager, sales and marketing, subsea systems, Australia and New Zealand, FMC Technologies.

And projects like Shell’s Prelude FLNG facility require newly engineered and designed subsea equipment to meet the challenges of supplying natural gas to the liquefaction facility for 25, 30, 35 or even 40 years. Other projects that have contributed to the evolution of subsea trees for Prelude and Wheatstone include Woodside’s Greater Western Flank, Perseus over Goodwyn and Pluto developments.

“I use the analogy that working offshore Australia is arguably as challenging as doing work in the Arctic, meaning that it is long distance, remote and difficult, and you don’t always have access 365 days a year,” he said. “You have to make equipment reliable so it does not fail. And you have to make equipment to be very available so there are redundant mechanisms and systems.” In addition, the equipment must be easily maintainable due to the limited access time window.

Managing obsolescence

In developing subsea systems for offshore Australia, FMC Technologies is designing and installing electrical, electrohydraulic and fiber-optic control systems on the seabed that need to work for 25, 30 or 35 years or more. The design and engineering are done to make sure those systems can be updated in the future either remotely or more easily if an upgrade needs to be done.

“We’ve also reengineered for management of obsolescence. If we think of obsolescence, we can just look at the phones in everybody’s pockets. Very few people are still running around with an iPhone 3, and that’s only two years old. You have an iPhone 5 or an iPhone 5S, and you’re waiting for an iPhone 6,” Robinson said.

“We’re doing everything we can to engineer equipment to allow future technological applications that are in the offing or may not even exist right now but that we know ultimately will be around. We make it simple so the system today can take advantage of improved technology availability in years to come,” he continued.

“The highest technology items on subsea trees and subsea manifolds, etc., are built into modules, especially Shell Prelude and Western Flank. You can leave the bulk of the subsea tree, which may be in the region of 50 or 60 tons or more, on the seabed for pretty much the life of the well,” he explained.

The modules contain sophisticated electronics, meters, choke and controls. The flow module, for example, contains the choke and a meter. It is the module that will see the high-velocity flow and over time may see some erosion. That module can be recovered and replaced. It’s a smaller unit that weighs anywhere from 5 to 10 tons depending on the design of the system, which means over time it is much easier to replace, he added.

Not only is the equipment designed for easier maintenance, but FMC Technologies also assists the operators by ensuring that it can interface in the future with subsea compression and separation. “If they can install compression subsea, [it offers] the operators more efficiency than they can [get] on a platform. From a capital cost standpoint, it would be significantly less than if it was on a platform or facility with people,” Robinson said.

Western Australia subsea projects

For the Woodside Greater Western Flank 1, those trees are built, and some of them are installed. The subsea manifolds for those are physically installed on the seabed, he continued.

“We’ve built a number of the Shell Prelude trees in Malaysia and Singapore. The manifolds are still being manufactured right now for Prelude—large-bore manifold systems. Then for the Chevron Wheatstone Project, the trees are being built in Malaysia and Singapore—again, large-bore 7-in. inside diameter (ID). The large-bore manifold and tie-in systems are in manufacture at a fabricator in China,” he added.

“All of these systems feature the latest generation of FMC Technologies subsea controls. Again, for these last gas projects the design life of the equipment is extended. Typically, the design lives are 15, 20 or 25 years. In some of these projects, we are being asked to design equipment that has a 25-, 30-, 35- or 40-year design life.

“What that means is we’ve used our latest generation of subsea control systems, and these have the ability to add in fiber optics. They can be upgraded in the future,” he explained.

Western Flank 1

The latest project FMC Technologies did for Woodside was Greater Western Flank, involving the latest version of the 5-in. ID enhanced vertical tree. Greater Western Flank is a classic Australian gas project with large amounts of infrastructure on the seabed initially but only a small number of subsea wells to be installed.

“Because it’s producing gas, typically what you will do is phase the installation of trees and wells over a long period of time. The Greater Western Flank project is capable of handling up to 22 subsea wells, and it has enough connection systems sitting subsea for that. But it will only start off life with approximately five wells being installed,” Robinson explained.

Phase 1 will develop the Goodwyn GH and Tidepole fields via a subsea tie-back to the existing platform.

Prelude trees tied to FLNG vessel

“The most exciting example of subsea development in Australia is the Shell Prelude Project, where we’re supplying the subsea systems specially engineered for Shell’s Prelude FLNG vessel. The wells will be sitting subsea and will be very closely tied back to the FLNG system above them,” Robinson said.

Normally there is a large distance between the subsea equipment and the host facility. In the case of Prelude, the gas is literally going a couple of kilometers directly above the seabed. That has driven some different requirements as far as reliability and availability in the system. There are also some system design aspects because the subsea wells and the FLNG vessel are so close, he added.

The latest version of the large-bore subsea trees are 7-in. ID and 10,000-psi working-pressure (WP) trees designed for very high volumes of gas. Prelude has 12 well slots, and six to seven trees will probably be installed in Phase 1.

The subsea systems underneath Prelude are not just the large-bore trees into the two manifolds that were provided. These feature the latest manifold tie-in connection systems, which are actually horizontal.

“For simplified and more cost-effective installation, take a look at the product. It is what we call a very available system. It’s going to be very reliable. It has multiple paths for the flow of gas from these wells to get to the FLNG, providing redundancy in the overall system. That was something that was quite different than the way they used to do it in other subsea systems because of the linkage to the FLNG,” he explained.

Wheatstone subsea tree configuration

FMC Technologies is also delivering to the Wheatstone Project a large-bore gas system—7-in. trees, 10,000-psi WP—but a different configuration than what is on Prelude. Wheatstone has 20-plus well slots available, and around half of those will be installed initially.

“Wheatstone has certainly pushed technology boundaries and limits. It’s enhanced them, raised the bar certainly on the size, type and capability of the subsea trees. These have some unique design requirements from the reliability and robustness standpoint, manifold connections in the current systems, the size of the manifolds and the thermal insulation needed,” he said.

“Wheatstone features a very robust, increased-functionality and higher standard subsea completion workover riser system with the ability to test and intervene in wells. They’ve raised the bar as far as a standard is concerned for that,” he continued.

The 7-in. tree systems are based on FMC Technologies’ enhanced vertical deepwater trees. Its 5-in. version of the tree has been used for many years. “We’ve basically taken all the lessons we’ve learned and the best features of those, using them in the 7-in. version of the tree. The larger bore means larger mechanisms are needed to seal the various items on it,” Robinson said.

Much higher temperatures required a redesign of some elements. Metallic seals are used to allow higher temperatures in many areas.

The high-volume gas wells will ultimately produce some sand that will likely cause erosion over time. “We’ve had to be cognizant and very specific in engineering the trees to minimize the flow velocity through the tree system to maximize the life of those. That was a design change,” he emphasized.

Enhanced vertical trees

The enhanced vertical tree arguably has taken the best features of the previous generations of vertical trees and the current versions of horizontal trees and combined them into one subsea tree, he continued.

The tree is being used in Australia by two different customers in two different ways. One of the customers will install and flow-test and then intervene in the wells traditionally with a completion workover riser system.

“Another customer will use more of a horizontal well intervention technique using a subsea BOP stack and subsea test trees to intervene on the well. That a few years ago could not have been possible because no vertical tree existed that allowed that to happen. But our enhanced vertical tree allows the functionality. It can either be intervened upon like a vertical tree or a horizontal tree in that the BOP can be installed on top of the tree, giving the customer more flexibility,” Robinson said.

FMC Technologies has large-bore trees installed in Australia that are flowing anywhere from 10 MMcm/d to 10.1 MMcm/d (350 MMcf/d to 400 MMcf/d)—maybe even in excess of that.

“We also want to make sure we design things for future enhanced recovery techniques,” he said. “We want to design things that enable the subsea systems to be worked over as technology improves in 20 years’ time. We’ve got a joint venture with Edison Chouest Offshore in FTO Services in a riserless well intervention system.

“We significantly raised the bar on the completion workover risers. While this is not classed as a BOP per se, the capability of those systems has now been increased significantly such that they are now able to cut and seal much larger diameters of equipment. Their ability to cut and seal is a lot more robust.”