ONS 2016: Safely pursuing continued service for aging assets

By Luiz Feijo, ABS on 8/31/2016

Getting the most out of an offshore unit is always the objective of the asset owner, but meeting safety requirements is equally important. So when floating production units (FPUs) are beginning to reach the end of their design life, the obvious question to ask is, “How much longer can this unit continue to operate safely?”

Most floating production units deployed on deepwater fields are designed and built based on a specified design life that for the most part is intended to match the expected life of the reservoir it will produce. Today, the industry is facing a situation in which the global floating offshore production fleet is aging, and many of these units are reaching the end of their original design life.

There are many scenarios that lead operators to consider extending the life of existing assets for continued services. A common situation is a field that is being produced by a facility that was designed and installed when the geological information on hand led to the conclusion that the reserves volumes were smaller than they actually were. The reserves volume determined the field life expectancy, which was used when designing the FPU. Later, improved geological data led to a new assessment of the reservoir size, resulting in a reservoir that was larger than originally expected. The end result it that the FPU reaching its design life was deployed on a field that was nowhere near being depleted.

Another situation that leads to the need for an FPU to remain on site longer is recovery technology advances that prolong the life of wells, making their production economically viable for a longer period of time.

A third common scenario is the discovery of new oil fields in the vicinity of existing assets that create tie-back opportunities. In this case, the evaluation needs to assess the unit to be sure it will be suitable for the new production well tied back to it.

The decision to extend the life of an asset is based on a number of essential evaluations, the first of which is to verify that the unit is able to safely operate beyond its design life. That requires assessing critical components—the structure, mooring, tendon systems, stability, machinery, etc.—to determine if they are fit for continued service. And to assess these components effectively, there has to be a baseline from which to work.

Through its international research and technology centers, ABS has partnered with academia and industry to set processes and criteria that address these and other key considerations for life extension. The process includes evaluating a series of elements, including the current physical conditions of the asset, availability of records and drawings, and the asset structural integrity. Based on the available information, an evaluation of the remaining fatigue life is performed to determine the suitability to remain in service.

The steps in determining the viability of an FPU for continued service include:
1. Determining a baseline for the unit’s current conditions taking into account historical operational data.
2. Assessing the status of the unit and actual usage using analytical tools and engineering software.
3. Determining the remaining safe operational life of the unit and delineating any necessary remedial action.
4. Establishing a path forward with regard to conservation and asset integrity management.

Classification societies follow industry trends, developing and expand Rules and Guides—based in part on industry input—so they keep pace with needs. A case in point is the recent release of ABS Guidance Notes on Life Extension Methodology for Floating Production Installations. The goal is to provide a process of verifying the adequacy of an FPU to withstand the design operational loads and to make sure updates and refurbishments will accommodate current requirements and any additional equipment needed onboard. The guidelines apply to ship-type installations, column stabilized installations, tension leg platforms (TLPs), Spars and hybrid designs. While the guidance is not applicable to mobile offshore drilling units, it provides a way to determine if a given FPU is fit for continued service.

The guidance document provides detailed steps for assessing an FPU for possible life extension for continued operations at the same location and provides a methodology for those units that are required to undergo modifications and improvements in order to remain in service.

By spearheading life extension initiatives and conducting studies and analyses for deepwater production units, ABS is setting a precedent for life extension for continued service of FPUs around the world.

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