Extreme water depths and low reservoir pressures of the Perdido development in the Gulf of Mexico (GoM) were particularly challenging for the engineering teams faced with tying multiple subsea completions and lifting the production stream 8,000 ft (2,439 m) from the seafloor to the production facility. It was obvious that natural formation pressure was insufficient todeliver the production liquids to the surface and that some form of artificial lift would be required.

According to Dusty Gilyard, senior completions engineer at Shell, who has been working on Perdido since the project’s inception, Shell considered several types of artificial lift, but ultimately decided electrical submersible pumping (ESP) systems were the best proven technology with a track record of reliable operations.

“Shell looked at two major suppliers,” Gilyard said. “Baker Hughes was selected because it had a proven track record with capable technology and the best system to support it.”

The Perdido spar

The Perdido spar, in approximately 8,000 ft (2,439 m) water depth in Alaminos Canyon Block 857, is the GoM’s deepest water production facility. (Image courtesy of Shell)

In January 2006, Shell awarded Baker Hughes Inc. contracts for seabed production boosting systems at two deepwater subsea projects: BC-10 offshore Brazil and Perdido in the GoM. Perdido is the first development in the GoM to use ESP systems in seabed vertical booster stations.

Unique, Purpose-Built ESP Systems Designed

ESP booster systems offer several advantages over alternative methods, including deployment from vessels of opportunity, redundant designs to maximize run time, and configurations that use existing infrastructure to house the ESP systems. These features provide operators economic solutions to maximize production from subsea fields.

Shell contracted Baker Hughes to provide five Centrilift XP enhanced-run-life ESP systems as well as engineering design, qualification, and testing services. Each system installation included a liquid/gas separator to maximize ESP system performance. The vertical booster stations were designed to handle production from three subsea satellite fields tied back to the Perdido spar host facility.

The 1,600-hp ESP systems were to be installed in five 350-ft (107-m) long caissons connected directly to the platform’s top-tensioned production risers. Three have been installed, and the remaining two will be in place by the end of 2011. The caissons lie directly beneath the spar production facility. Each caisson is equipped with cylindrical-cyclonic gas separation systems to separate natural gas entrained in the fluids before the fluids enter the ESP system.

Each pumping system can deliver between 10,000 and 30,000 b/d of liquid. For this application, the pumps were designed for approximately 20,000 b/d. If all five systems run at nominal flow rate, the platform can deliver about 100,000 b/d of production. The ESP systems also control the spar riser head pressures.

“In the case of Perdido, the wells would not naturally flow to surface, so we needed something that would handle the boost and was extremely reliable,” Gilyard said. “We plan to pump 100,000 b/d of oil, and unless all five pumps are working, we’re not going to make our goal. We needed the caisson on the ocean floor so the wells could flow to it and we could pump the fluid to surface.”

Design Pushes The Limits

Before installation on Perdido, adjustments to the systems were necessary to meet the requirements of the deepwater development. Both Shell and Baker Hughes conducted extensive research to design ESP systems for this application.

Illustration

Inside the caissons are 1,600-hp Centrilift XP ESP systems that boost produced fluid from the seabed to the spar. (Illustration courtesy of Baker Hughes Inc.)

Early in the project, Baker Hughes was involved in pre-engineering for this unique application. The ESP system design had to take into account all of the possible pumping scenarios at Perdido. Much of the application engineering work was done to ensure the best possible design to match the required operating conditions. Technology planning considered varying potential operating conditions such as required boost pressures and flow rates – all while considering a multitude of fluid compositions since production fluids from each well would be commingled at the ESP systems.

More than 200 scenarios were modeled to determine the system that would work best in the application. Shell’s front-end engineering requirements included thorough qualification testing of the new designs. Because of the unique challenges of this installation, the companies worked together to define the expected demands on the ESP systems while also reviewing the run life and history of the technology. Design details were validated on components as specific as the type of elastomer used on a seal.

“The most critical aspect was the functionality of the ESP system,” Gilyard said. “It needed to work in any type of environment.

“The ESP was put in a subsea separator system and tested for operability using different monitoring functions and level control methods. We considered combinations of multiple temperature and flow rates. The pump had to be able to work both mechanically and electronically without any gauge interference.”

Some enhancements were developed to meet the run life expectations of the project. One of these was changing the configurations of the seal section to include an extra chamber. A standard seal configuration for this size of equipment has two chambers, but a third was added for redundancy. Two seal sections were run in tandem, providing six chambers.

Another new technology development was the thrust bearing in the seal. Based on the application review, it was determined that the existing highest capacity thrust bearing in the seal was insufficient in some pumping conditions. A new enhanced high-load thrust bearing was designed and qualified to account for maximum pump thrust.

Installation Hurdles Resolved

The engineering team also designed specialized installation equipment to meet Shell’s requirements, including new tooling to meet the lifting and hoisting standards. New equipment baskets, lifting subs, and control line push arms were created as well.

Baker Hughes’ intelligent production systems (IPS) group designed new equipment for the project as well, including special spooling units that deployed the heavy armored power cable that supplies electricity to the ESP motors. Normally, 8,500 ft (2,591 m) of cable would be supplied on two reels and spliced together during installation. Shell specified that the ESP cable needed to be on one large reel to avoid switching the reel on the platform. With the help of the IPS group, a heavy-duty spooling unit that could advance and take up the cable as it was run was developed along with transportation frames that could store extra cable or an empty reel.

The Project Continues

Baker Hughes continues to contribute to the success of Perdido. By year-end, all of the ESP systems will be installed in the five vertical subsea boosting stations. This will be a long-term relationship as the project switches from installing to sustaining to ensure reliable operation of the production systems. Over time, as production increases, the two companies will collaborate to maximize the performance of the systems and optimize production.

The project was an important learning experience for everyone involved. The technology developed for Perdido and BC-10, along with the lessons learned from working together as a cohesive team, have advanced subsea development capabilities for the entire industry.