Remaining Life Assessment of Subsea Jumpers, Flowlines & Risers

GATE was engaged to evaluate the current condition and remaining life of the subsea jumpers and flowline of a deepwater oil and gas facility in the Gulf of Mexico.

The subsea field, which was comprised of multiple oil wells, was produced at a Tension Leg Platform (TLP) with a nominal capacity to produce 100,000 barrels of oil and 50 million cubic feet of gas per day. The subsea and topsides facilities were designed to operate with an expected maximum carbon dioxide (CO2) concentration of 0.15 mole percent from any given producing well. However, from 2015 onwards, the CO2 concentration in the export gas was measured to be approximately 0.4 mole percent. This concentration was measured following commingling of all producing wells and, therefore, it was likely that individual wells were producing gas with a higher CO2 content.

The objectives of the study were to:

  • Calculate the possible remaining wall thickness of the flowline and jumpers.
  • Calculate the remaining life of each flowline and jumper.
  • Provide recommendations to perform a cost-effective subsea inspection to validate remaining wall thickness.
  • Develop a fit-for-purpose subsea corrosion management plan to ensure that the flowlines and jumpers adequately meet the expected design life.

Challenge

To develop a corrosion management and subsea inspection plan for an operating facility in a short time frame while managing multiple stakeholders such as field operations, production engineering, facilities, engineering, and chemical vendors.

Solution

A team of integrity management, corrosion, production chemistry, and flow assurance experts from GATE collated and evaluated available operational data to calculate the remaining wall thickness of the subsea jumpers and flowline.
This data was used in conjunction with the expected production profiles from each well to determine whether the given system could safely produce for expected remaining life without additional monitoring or intervention.
Where necessary, appropriate inspection and corrosion mitigation plans were developed and implemented combining the use of corrosion inhibitor with topsides monitoring and subsea non-destructive testing.

Technical Achievements & Benefits

  • GATE implemented a systematic corrosion risk assessment methodology based on stakeholder agreement which used available data to risk-rank each jumper and flowline. The jumpers and flowlines were assigned three different risk ratings – low, medium, and high. The risk ratings were defined based on calculated wall loss, current operating pressure, maximum expected operating pressures and water cuts for the remaining life of the wells producing through each jumper and flowline. A detailed inspection and corrosion management plan was assigned to each component within a given risk level.
  • The resulting project recommendations enabled the client to develop a cost-effective subsea inspection and corrosion mitigation plan that would allow them to produce without the risk of loss of containment.