Offshore topside life extension – from a structural perspective.
Geir Stenvaag, Head of Structural Integrity, provides his outlook on life extension and structural assessments of offshore topsides.
Incentives for life extension
“When a platform or oilfield is initially planned, it’s designed according to the size of the reservoir and will typically last about 20-25 years’ time. However, new technology continuously makes it possible to extract more from existing reservoirs and detect additional reservoirs in nearby locations.
Conceding its obvious financial upside with not having to develop an entirely new field, it poses challenges from both a structural and a requirements perspective. Will the structure be able to withstand 10 or 20 new years of waves, vibrations and general fatigue? Not to mention, will it be able to meet new, more rigorous, government requirements?
A structural assessment
There are several aspects that are considered; topside weight, changes in environmental loads, fatigue in e.g. the flare tower, as well as changes in the seabed. Higher waves and a descended foundation may result in waves hitting deck. A new module or a heavier topside will typically result in the need for a reinforced foundation and topside.
It’s important to ensure that the structure is assessed from all perspectives to ensure continuous operation with a high level of safety in order to meet todays’ stringent requirements. Even considering the fact that naval vessels have increased substantially in size since we started designing offshore platforms.
The incentive to meet all these requirements with an existing solution or a modification is generally strong – the alternative is typically far more time consuming and costly.
A more cost efficient approach to life extension for the future
Creating clear standards and guidelines for life extension to be included in the early design phases that provides a reserve or leeway for expansion and extension of service life. These guidelines should be based on statistical evidence from previous cases and should provide both a best practice, but also a minimum in terms of how much extra weight should the structure be able to withstand – 10 % / 20 %? What is typically needed?
Designing for this in the beginning will generate less obstacles in the future when times have changed and technology has opened up inevitable new doors.”