Industry and private consumers depend on oil and gas pipelines that stretch for thousands of kilometers under water. It is not uncommon for deposits to clog these pipelines. Until now, there have been few ways to identify the formation of plugs in-situ and non-destructively. Neutrons can make this much easier, as measurements at the Heinz Maier-Leibnitz Research Neutron Source (FRM II) at the Technical University of Munich (TUM) show.
Oil and gas pipelines are the arteries of our energy supply. Like the Nord Stream pipelines, they transport the energy sources over long distances under water to storage and production facilities on land.
But it’s not just supply bottlenecks that can lead to supply problems. Under certain conditions, the mixture in the pipelines, which typically consists of gas, oil and water, can become very viscous and even form solid phases.
Solid hydrates that form from gas and water are particularly troublesome for operators, such as when the mixture cools to the low temperatures of the seafloor during prolonged pipeline shutdowns.
Previous approaches do not work underwater
To fix a blockage in the field, the first step is to find the affected section of the pipeline. Because it may have formed anywhere along the pipeline, locating the blockage from the outside is a major challenge.
So far, thermal imaging cameras and gamma rays have been used to detect the blockages. However, none of these methods work under water. Ultrasound, on the other hand, penetrates water easily, but the pipeline wall means that hydrate blocks can only be seen at close range from the outside.
Since underwater pipelines are laid at depths of up to 2000 meters and are often naturally covered by seabed materials such as sand or silt, this raises further practical difficulties. In addition, the acoustic impedances of the hydrate phase and other phases of the crude oil mixture hardly differ.
Neutrons as the perfect probe
TechnipFMC, a company specializing in subsea pipelines with about 20,000 employees worldwide, was “looking for a more efficient method to detect such plugs in a non-contact, non-destructive and reliable way despite thick walls,” says Dr. Xavier Sebastian, a project manager at the company.
“Neutrons are the perfect probe for the task at hand,” Dr. Sophie Bouat, CEO of Science‑S.A.V.E.D. (Scientific Analysis Vitalises Enterprise Development) then suggested, putting the company in touch with scientists at the Heinz Maier-Leibnitz Center in Garching, near Munich.
“With prompt gamma neutron activation analysis, light atoms and hydrogen in particular can be detected very accurately,” she continued. Since hydrates as well as oil and gas differ considerably in their hydrogen content, it should be possible to detect blockages by measuring the hydrogen concentration.
Feasibility study at FRM II
Dr. Ralph Gilles, industry coordinator at the FRM II research neutron source, conducted a feasibility study on this topic together with other colleagues from the Technical University of Munich and the Forschungszentrum Jülich.
With the PGAA (Prompt Gamma Activation Analysis) instrument, which uses cold neutrons from FRM II, the research team scanned samples and was able to prove that it is indeed possible to distinguish between oil and gas or the plug in this way.
Using the NECTAR radiography and tomography facility and the FaNGAS (Fast Neutron Induced Gamma Ray Spectroscopy) instrument, they demonstrated, with the help of fast neutrons from FRM II, that a sufficiently large number of neutrons penetrate the metal walls of the pipeline to enable the respective measurement, and that the measurement also works well under water.
A small neutron source detects plugs
“Our experiments have also shown that we can even distinguish a plug in the making from a fully developed blockage. That’s very beneficial, because then you can even preemptively heat a pipe segment to melt away the blockage before it fully forms.”
- Dr. Ralph Gilles
In practice, a mobile detector with a small neutron source moves back and forth along the pipeline to look for plugs. “We are very pleased that, with the help of the measurements at the research neutron source, we have now found an efficient method that will make it much easier to find these plugs in the future,” says Dr. Xavier Sebastian.
