Medical technology has been taken to the bottom of deepwater Gulf of Mexico to help operators understand their flow assurance and asset integrity issues. Elaine Maslin explains a technology first.
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Discovery deployed. |
In an industry known for its long lead times from technology invention to deployment, Tracerco’s Discovery stands out.
Discovery is a non-intrusive subsea CT (computed tomography) scanner, based on medical technology, developed to inspect pipelines from the outside. The Discovery concept started life about two years ago. Today, it is a fully developed 1.2-tonne piece of kit that has successfully made it to the bottom of deepwater Gulf of Mexico (GOM) to scan unpiggable pipelines for Shell.
The 1.5m-diameter tool has already racked up several awards, including a “Spotlight on New Technology” win at the 2015 Offshore Technology Conference and the inaugural “UTF Subsea Project Award” at the Underwater Technology Conference in Bergen. Discovery enables 360° inspection of unpiggable 6-27in-diameter pipes without the need to remove protective coatings or interrupt production. It creates high-resolution CT scan of subsea pipelines, distinguishing between wax, hydrate, asphaltene or scale deposition at density differences of 0.05g/cu cm, as well as showing weaknesses and wall thinning of flowlines – all with real-time data sent topside.
It can also be used on pipe-in-pipe applications, including detecting water ingress between pipes, allowing both the inner and outer pipeline in a pipe-in-pipe system to be inspected from the outside.
Having completed its first deployment on Shell’s subsea Europa field in the GOM, Tracerco ordered more units, intending to have three based in Houston and two in the UK. In coming years, the company plans to increase that to 12-20 units, Lee Robins, head of subsea services at Tracerco, told OE during OTC.
Drivers
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Tracerco’s Discovery before being plunged into the deep. |
Tracerco aimed to enable operators to assess flow assurance and integrity on unpiggable pipelines, Robins says. Tracerco, a subsidiary of UK-based conglomerate Johnson Matthey, used its experience with gamma ray scanning technology to address the problem, thus developing the Discovery concept.
“Sometimes a pipeline is unpiggable because you do not want to stop production or get a pig stuck in the pipeline,” Robins says. “If you detect something with a smart pig, you could then go and look at what it is.”
Don Nelson, subsea specialist at Shell, Houston, has been working with Tracerco on the project. “There are many systems that are not smart-piggable, for a variety of reasons,” he says. “The closer you get to the well, the less likely you are to have intelligent pigging capability.”
According to the US Bureau of Safety and Environmental Enforcement, there’s some 20,000km of pipeline in the GOM, Nelson says, mostly single wall, but often with a protective coating, making inspection difficult.
Pipe-in-pipe inspection can be even trickier. “If pipe-in-pipe pipelines are piggable, you can get internal wall loss data by sending an intelligent pig through. If they are not coated, you can get wall loss data on the outer pipeline. Discovery is the only one that gives you real time information on both pipelines and the contents at the same time,” Robins says.
The CT scanner, which can go to 10,000ft deep, is deployed from its own basket, launched from a vessel, and then moved and controlled subsea using a work class ROV. Scans are then performed at locations along the pipeline.
Depending on the task the tool is performing, scans take more or less time. A scan for asphaltenes, for example, would take 3-5 min. For the definition required to assess wall thickness, a 10 min scan would be performed, especially if it’s a pipe-in-pipe system.
Europa
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Lee Robins. |
Discovery underwent trials at both the Underwater Centre’s test site in Loch Linnhe in Scotland, and at NASA’s facilities in Houston, before it was taken to depth in a piggyback trial. The Europa subsea development is 140mi (225km) southeast of New Orleans in 3900ft (1190m) water depth. First oil was in 2000 via the Mars tension leg platform.
During a two-month period in late 2014, Tracerco and Shell used Discovery to test about 60km of flowlines on the Europa project, including pipe-in-pipe.
The Europa pipe-in-pipe system is 12in nominal outer diameter (including coating), 8 5/8in internal outer diameter and had a combination of flow assurance and integrity uncertainties. Shell wanted to know where and what the deposits were.
“This is the first time such a complex instrument has been taken to bottom of the Gulf of Mexico,” Robins says. “We were all sat there crossing our fingers. We managed to do over a couple of hundred scans, explore really long lengths of the pipeline.”
For Nelson, the Discovery deployment on Europa was to assess flow assurance and asset integrity on two flowlines. “On the asset integrity front, we saw what we expected. We didn’t have any wall loss,” he says. “On the flow assurance side, one line was in a flowing condition and one was shut-in. This [the results] will drive our remediation strategy for the line with the heavier deposition. On the line with lighter deposition, we have changed our operating conditions.”
While similar types of scans could be done already, using Tracerco’s Explorer technology, this has lower resolution – it has one source and one detector – and analysis is dependent on cross-sectional density profiles in discreet locations, i.e. not a full 360° scan. “This is like an X-ray, compared to the CT scan performed by Discovery,” which has one source and 100 detectors, Robins says. “It offers more clarity, more information, and you are able to see if a deposit is wax, asphaltene, scale or a gas trap. Before, we could only see where there was a problem.”
For Shell, both technologies can be used in conjunction, using Explorer to do an initial, faster assessment, then targeting problem areas with Discovery. Explorer, which is also a relatively new technology, has already been used on several subsea flowlines, including a project in the North Sea, as well as a campaign in the Gulf of Mexico.
Tracerco now hopes Discovery will be deployed worldwide. “The technology is proven, we look forward to seeing it expand,” Robins says.
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