Sound technique to unplug oil
Oct 1, 2008
Oil may be slippery stuff, but when it is pumped from the seabed to the water surface it can cool and precipitate thick deposits that block the inside of the pipes used to transport it. Although engineers can clear such blockages by sending in robots known as pipeline inspection gauges or “pigs”, these sometimes get stuck themselves, forcing the engineers to find ways to remove them or even spend millions replacing the pipeline.
Now a Norwegian scientist has developed a simple technique that could substantially cut costs of clearing blockages. Jon Steinar Gudmundsson of the Norwegian University of Science and Technology uses the pressure pulses created when oil flow is shut off to work out the size and location of a blockage, so that engineers can know exactly what size of pig to send in.
Gudmundsson’s technique, which he is selling via a company he has set up, involves abruptly closing the valve at the end of the pipe, thereby cutting off the oil which is being forced upwards by the weight of the ocean and seabed. The resulting change in momentum initiates a pressure pulse within the oil, which travels back down the pipe at the speed of sound.
I always used to see the needle in the pressure gauge flicker and I was curious as to why it did so Jon Steinar Gudmundsson, Norwegian University of Science and Technology
The downwards pulse continuously halts the oil in its path, transforming the energy that is previously dissipated via friction through the pipe wall into new pressure pulses that travel back up towards the valve. In this way the oil pressure beneath the valve, which is already high when the valve is shut, continues to rise steadily as the backward pulses arrive.
Any blockages in the pipe superimpose an additional rise in pressure on the slowly increasing background. A pressure sensor positioned just under the valve will therefore reveal both the position and the size of a blockage — with the position related to the time of arrival of the pressure jump (given by the speed of sound through oil) and the size proportional to the magnitude of the jump.
Gudmundsson, who worked for many years on geothermal wells in Iceland, says the inspiration for the new technique came after noticing that the pressure at the head of a geothermal well always rose very quickly when the valve was closed. “I always used to see the needle in the pressure gauge flicker and I was curious as to why it did so,” he explains.
After visiting a number of offshore oil platforms in Norway and making use of their modern pressure transducers he realized he could quantify this pressure change and use it to measure pipeline blockage. He patented his technique and has now commercialized it via a company, Markland Technology, which he spun out from his university. He says the technology has already been used at several offshore oil platforms in the North Sea, and that he expects other platforms around the world to take it up.
About the author
Edwin Cartlidge is a science journalist based in Rome