Smart extension of platform lifetime
Responsible use of natural resources 17 May 2016 Ulf Tyge Tygesen
High-tech measurements can minimise the cost of maximising recovery from existing oil and gas fields. Ground-breaking technology, says a professor at the Danish Hydrocarbon Research and Technology Centre.
Extending the lifetime of offshore structures is a growing trend in the global energy business. Offshore operators need to ensure that platform structures have sufficient strength to carry their loads safely. Operators are usually able to extend the lifetime of their facilities according to risk- and reliability-based inspection planning, or they can opt to reinforce the structures at considerable cost. Either way, the lifetime extension process entails heavy investment.
“Today, older platforms are inspected at intervals specified by norms and best practice. But it is not possible to inspect all parts of a platform, so finding a cost-effective means of monitoring how the entire structure is doing gives us a much better basis for deciding how often to inspect and where to inspect,” says Rune Brincker, Professor and Head of Structural Integrity Research at the Danish Hydrocarbon Research and Technology Centre.
“Structural health monitoring (SHM) is a ground-breaking technology that can dramatically increase our knowledge about waves and fatigue. SHM can help scope our risk management efforts and potentially reduce operating expenditures for platforms during late field life,” Rune Brincker concludes.
SHM combines a variety of sensing technologies with an embedded measurement controller to capture, log and analyse real-time data.
Strain gauges, accelerometers, wave radars and GPSs are mounted on the platform topsides in order to transmit real time information about the loads affecting the platform. SHM has been around for a number of years, but the really innovative thing is that we found a way of converting SHM data and feeding it into the existing finite element model of the platform. Using advanced calculations, we can determine the actual state of the structure.
Hess continued its operation
The Hess Corporation continually invests capital in the Danish North Sea to extend production from the South Arne field. In 2014 the oil and gas company had to meet the challenge of a substructure with a low fatigue design life, for which reason Ramboll carried out wave load calibration and a re-assessment analysis by post-processing data from both SHM measurements and wave basin laboratory tests.
The data showed the platform structure to be better than anticipated, and Hess was able to obtain authority approval for its continued operation without incurring the high costs associated with platform reinforcement and retrofit designs.
Morten Nielsen, Integrity Advisor at Hess, says: “Lifetime extension is not always about adding steel to existing structures, but is much more about utilising what is already there. With a high-quality installation, it is reasonable to anticipate that we can gain many more years of operation than the original design lifetime would suggest.”
SHM also has promising perspectives for offshore structures of the future. The knowledge gained from actual fatigue load scenarios on existing platforms can be incorporated into new platform designs, thus making them more cost-effective.
The International Energy Agency predicts that by 2040 the world will still depend on oil and gas for 50% of its energy supply. With mature fields representing an ever-growing segment of global offshore reserves, there is a keen interest in maximizing recovery from existing oil fields to keep up with global energy demand.
Ramboll also extends the lifetime of offshore structures with:
- Reliability-based inspection planning
- Structural reinforcement
- System upgrades and revamps
- Production optimisation
- Late field life rationalisation