Monitoring Developments In The Gulf Of Mexico

Pulse wins EPIC contract for riser and tensioner monitoring system.

Pulse Structural Monitoring is developing a riser and tensioner monitoring system for the Big Foot extended tension leg platform (ETLP) in the Gulf of Mexico, which Chevron will operate. The system will actively monitor riser motions and bottom currents in real time and key parameters such as tensioner pressure, stroke inclination and lateral loads on the riser and tensioning system.

This is Pulse’s first engineering, procurement, installation and commissioning (EPIC) contract from Chevron. The company won the contract in August 2012 and is working towards a delivery deadline of April 2013.

The Big Foot development is in the deepwater Gulf of Mexico approximately 360 km south of New Orleans, Louisiana, USA, in water depths of 1600 m. The field lies in the Walker Ridge area and contains total recoverable resources in excess of 200 MM bbl of oil equivalent. First oil is anticipated in 2014.

The Big Foot ETLP, which is currently under construction in Korea, will have a production capacity of 75,000 bbl/d for oil and 25 MM cf/d for natural gas. It will feature dry trees and top-tensioned risers, and will have full drilling, workover and sidetrack capabilities on the topsides. A push-up-type tensioner system will enable the ETLP to withstand the harsh conditions prevalent in the area. Modelling indicates that the platform should be able to withstand a 1000-year hurricane.

“As part of the preliminary work for the development,” says Wolfgang Ruf, vice president, Pulse, “we have been asked to assist with testing the riser tensioner system. The tensioner uses six push rods to maintain tension. Chevron wants to establish what would happen if one of the rods failed and how it might affect the stability of the system. We will hook up the tensioner and install a monitoring system to track performance during the test. This will be a key design qualification testing milestone.”

The Pulse riser and tension monitoring system aims to offer comprehensive understanding of the risers and wellhead’s performance under severe conditions. It will also provide information the operators can use to accurately measure and quantify fatigue damage to the risers and wellhead. The data, especially from during severe environmental events, can be evaluated offshore or transmitted onshore on demand for further processing and integrity management activities. This information will be invaluable for future drilling operations in similar conditions.

Significantly, the work is taking place under an EPIC contract, i.e., the Pulse system is being supplied as an integral part of the platform’s systems and will be fully integrated into Chevron’s control system. The main driver for Chevron is to monitor the integrity of the structure and to ensure that it has a clear understanding of the condition of the risers and tensioners so that operations can be conducted safely and efficiently.

Post-Macondo, structural monitoring has become an increasingly important aspect of operations and is now considered during all stages, from obtaining approvals through to improved management of operational risk. Operators are increasingly focusing on improving the integrity of their operations; monitoring plays a key part in the integrity management process.

Pulse has a long history of providing systems for integrity monitoring to enhance safety and improve efficiency. “Since 1998, we have completed more than 500 deployments to depths of more than 3000 m,” says Ruf. “The contract for the Big Foot development builds on this track record and on the successful completion of a similar project for the recent Tahiti development. As on the Tahiti development, we will be working with our sister company 2H Offshore. They will provide engineering and delivery of the riser system for Big Foot.”

One potential issue for the Big Foot ETLP is the possibility of deep currents affecting its subsea systems. Loop currents are usually only an issue in the uppermost 150–180 m of the water column, but at Big Foot, they may occur at greater water depths. The platform will be close to a subsea escarpment, so there is the possibility of strong currents at depth.

Pulse will install an acoustic Doppler current profiler to measure current speed and direction. This will help to ensure that subsea operations can be conducted safely. For example, knowing the current strength and direction when a remotely operated vehicle is deployed could prevent it from drifting off in a strong current. Conditions near the seabed will vary and will need regular monitoring.

Ruf explains, “We are developing a solution to meet Chevron’s needs exactly, but one that uses a large number of standard components. The main challenges are dealing with the various companies and stakeholder groups within Chevron to ensure that we deliver the information gathered in the form they will find most useful and managing the interfaces to deliver full technical integration into existing infrastructure.

“There are some fundamental physical challenges too. Data transmitted from the seabed to the surface will be in real time. In addition to optimising the interface with Chevron’s system, we have the engineering challenges of managing a 4900-m-long cable in demanding marine conditions. We are building on experience gained in deepwater operations elsewhere in the world to deliver a sound and reliable monitoring solution."

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