Digital detail is key to conductor analysis

Louise Davis

The design, maintenance and monitoring of key components such as risers and conductors has developed considerably as the industry has matured. Today, highly developed digital technology is playing a huge part, not only in providing efficiency and cost savings, but also improving the safety of operations.

Conductor and riser systems must withstand all potential environmental conditions, but also need to be designed to contain the maximum pressure expected during operations.

The new approach to analysing and testing conductors

The obvious (but huge) benefit of analysing and testing conductor designs digitally is that it can be done very safely onshore rather than trying it out in the North Sea, waiting and potentially dealing with disaster. Any conductor and riser system can be modelled in the virtual world, with nobody in harm’s way.

Although this kind of data modelling has been used before, it is advances in the software and processing power that have allowed a huge leap in its capabilities. Tens of thousands of numbers can be inputted, millions of calculations can be conducted, with varying loads, conditions, materials and so on all factored in, producing far more accurate and less conservative results than ever before.

To date, the tendency has been to conduct this kind of analysis later in the development phase. With the plans drawn and the equipment ordered, it’s more often treated as a final check before work commences. Although there’s nothing intrinsically wrong with that approach, especially from a safety point of view, a considerable amount of equipment expense and time can be saved if the analysis is done early on in the process. Hundreds of real-world scenarios can be modelled relatively cheaply and quickly in the analytical world, pushing the boundaries that would have been too inefficient in paper-based systems.

Harnessing this new era of high-powered computer models removes conservatism from the design stage because impossible or inefficient options are quickly ruled out or refined. In doing so, more cost-effective and streamlined designs have the opportunity to emerge that are still fit-for-purpose.

Integrated teams and actionable outcomes of conductor design

This early stage analysis approach has recently been used to tackle a design feasibility project on a platform in the Norwegian sector of the North Sea. The installation had been active for around 15 years and the owner was looking to add two more conductors to enhance its production.

With two available conductor slots, the solution seemed obvious – almost beyond question. Two conductors would be installed in the two spare slots, maximising the use of the pre-existing infrastructure.

One question did remain, however. These vacant slots did not have all necessary lateral guide supports installed and therefore the conductor performance could be compromised. So, a means to provide this support had to be found.

A retrospective installation of a lateral guide support below water level was deemed very risky, as it would involve divers. Initially, the client planned to install two supports: one above the water level and one below the water level.

This is a hugely complicated job, particularly in a difficult North Sea environment. Aquaterra Energy’s integrated analysis and engineering team were brought in to show how this might be possible.

Reliable results following in-depth simulation and analysis

The analysts started by getting a comprehensive understanding of all the equipment within the plans and on site, including conductor design, water depths, environmental conditions, location of the guides and a variety of other different design specific parameters. The information was then used to build a representative computer model in specialist software, allowing the team to simulate exactly how the system could react under many different conditions. One of the key factors to simulate was the North Sea conditions, as when a storm hits the waves can induce considerable load and movement on the conductors. The loads were then read and compared to industry safety codes, which are set by API and DNV, allowing an accurate picture as to whether they were acceptable.

Not stopping there, the Aquaterra Energy team took this a step further, looking at higher-level models, varying ideas around how the support could be designed, where it could be placed and how it could be installed at a few different elevations. Ultimately, this was challenging the client’s idea to see if there were any better solutions available. With the analysis team being under the same roof as the offshore teams, it allowed potential solutions to be challenged on a feasibility basis, and therefore no solution was suggested that wasn’t possible to deliver.

Major savings and a new approach to the conductor design

Through open dialogue and collaboration between the client and analysts, a rather welcome result awaited in the data. The outcome of this assessment was significant and saved the client over £4million in project costs and additional untold savings on future maintenance. How? The analysis found a workable solution by only adding a support just above the water level. This was achieved by optimising the conductor pipe by increasing the wall thickness and designing out the need to install a support below the water level. This mitigated the need for an expensive second support and greatly simplified the planned operations.

Notably, divers were no longer required as the required support was above the water level, improving safety through reduced risk. As Aquaterra Energy works closely with its clients, the recommendation was made after liaising with the client to make sure it could obtain the required pipe size on time for the operations to begin.

Providing independent advice, quickly, gave a fresh perspective for this type of project in future. In today’s environment, where safety, efficiency and enhanced production are close bedfellows, it has been all too easy for the industry to go with what’s been done before – but new and advanced analysis supports the drive to optimisation in the 21st century.

Martin Harrop is riser analysis manager at Aquaterra Energy

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