Pressure release

A new method that uses a pressure pulse to locate blockages inside pipelines could help oil extraction on the ocean floor.

The technology from researchers at the Norwegian University of Science and Technology (NTNU) promises to speed up the oil production processes and reduce costs.

Based on the ‘water hammer’ effect, the principle is the same as the bang one can hear in a washing machine or dishwasher when the flow of water to the machine is shut off quickly.

The researchers create a similar ‘bang’ by closing a pressure valve on the pipeline flow-line. The valve is closed for a few seconds and then reopened. The resulting pressure pulse is recorded at two locations upstream of the valve with transducers.

The information gathered is then fed into a data acquisition system and put through complex analytical methods. The measurements are used to create a map of the inside of the pipeline.

‘We’re able to see where the blockage is and how much it is,’ said Jon Steinar Gudmundsson, who developed the method.

Operators are able to see on a computer screen where the next pressure vent is located. The information helps them choose the best possible method for clearing the pipe.

Gudmundsson said the ocean floor is a difficult environment on which to maintain and repair pipelines. There are few ways to do it that aren’t costly or time consuming.

One major cause of pipeline blockages is wax build-up. As oil passes through pipelines on the seabed it cools, leaving a wax layer along the inside of the pipe. The pipeline is then shut down and a robot has to be sent through to find the cause of the problem. In cases where robots gets stuck, operators have to close off the pipeline and reverse the pressure to eject the robot.

At other times, the robot has to travel through a long stretch of pipeline before it comes across a blockage. In either situation, blockage detection and removal can take a long time.

Lost production time can quickly become a costly affair. The Norwegian researchers estimated that if pipeline problems caused a platform to be closed for longer than several months, the lost revenue could be up to £10m.

The new blockage location method was developed after Gudmundsson observed the shutdown of a geothermal well in Iceland. He noticed that the well was closed with a pressure valve and this created a pressure wave. He realised that this pulse could be used for constructive means.

One of the advantages of using the pressure pulse method is it is inexpensive and requires very little installation. The hardware requirements are limited to the pipeline’s existing pressure valve and two transducers.

Gudmundsson said NTNU’s spin-off company Markland Technology, set up to commercialise the method, is looking to sell maintenance services to oil companies rather than equipment.

So far, Gudmundsson said Markland Technology has achieved success in offshore oil companies operating in Norway and Africa.