Research project: Detecting leaks from undersea gas pipelines, seabed methane reserves, and carbon capture and storage facilities

Currently Active:: Yes

An invention that is 100x more sensitive than commercial systems for detecting leaks from undersea gas pipelines

Project Overview

seeps and CCSFs — Monitoring plan for pipes,

What is the invention? Undersea gas leakages (from both natural reservoirs and manmade structures) represent environmental hazard on an immense scale. Professors Leighton and White (Southampton University) invented a ‘passive acoustic system’ for remote leak detection and quantification, capable of long-term monitoring because of its low power requirements. They considered leaks of three sorts:

from gas pipelines on the seabed;
from Carbon Capture and Storage Facilities (UK Government is providing around £1-billion for the first commercial-scale CCSF);
and from natural methane seeps (the per-molecule ‘greenhouse’ heating potential of methane is 20 times that of carbon dioxide, and the global reserve of methane in hydrate form is more than twice the worldwide amount of carbon in all known fossil fuels on Earth).

How does it work? When gas leaks occur underwater, bubbles are produced. At the point when it is produced, each bubble produces a note - recall the low notes in the bubbling noise made by scuba divers. The important things is that the smaller the bubble, the higher the note, just as a large wineglass emits a deeper note than a small wineglass when tapped with a spoon. The BBC clip of Professor Leighton explaining this is available below.

So when a leak occurs, each bubble ‘sings’ its own note: it is like listening to a choir singing, where each person sings their own note, but just once. Some voice overlap, some do not. Therefore by analysing the sound you should know how many bubbles are produced each second, and what size they are. That gives you the rate at which gas is being released into the water.

methane at low tide — Professor Leighton maps seabed

What are the advantages of using it? The beauty of the technique is that all it requires is the sort of underwater microphones (‘hydrophones’) that are readily available today. The technique itself comes from a set of equations that can be used to instruct a computer how to interpret those sounds in terms of the amount of gas released. As such it does not require any special new hardware, so is cheap to implement.
The second advantage is that, because the device just listens (i.e. is ‘passive’) as opposed to send out a sound pulse, it uses little power and so can monitor for a long time. It can even scavenge its power from the local water currents driving mini turbines, so never need refuelling.

The third advantage is its ability to detect small leaks at an early stage, before they grow: industry has said it is 100x more sensitive than current commercial techniques for the large, long undersea pipelines they use.

Why is it needed? First, a major technology for reducing the amount of carbon (and hence the impact of man on climate change) is to pump carbon dioxide from the atmosphere into the vast empty chambers created beneath the seabed by the previous extraction from them of oil and gas for fuel. This is called ‘carbon capture and storage'. Detection of any leakage from these storage facilities is important, because otherwise it would undo all the good work achieved in putting the CO2 down there in the first place. Early detection is important because a small leak is easier to fix than the large one it might well become in time, and because local leaks of CO2 could acidify the seawater and seabed and damage flora and fauna.

Second, the leakage of natural fuel gas from pipelines needs to be detected at an early stage, because (as stated above) small leaks can grow. It is wasteful for fuel to leak into the atmosphere, and polluting. Furthermore, large leaks can even destabilize structures such as platforms, endangering lives. In a related scenario, ‘blow-out' in oil drilling is a dangerous event for which such bubble detection might provide early warning: the operation of the ‘blow-out preventers' was implicated in the catastrophic Deepwater Horizon oil spill (also known as the Macondo blowout) in the Gulf of Mexico in 2010.

Third, natural reserves of methane in the seabed do release bubbles, but rising temperatures (as a result of manmade climate change) could increase the rate at which natural methane escapes from the seabed. This could lead of an enhanced greenhouse effect, creating a vicious circle. Monitoring of the rate of gas release bubbling of natural methane reserves is therefore very important.

What is happened with the system now?
Carbon Capture and Storage: In 2012 the invention successfully detected leaks in the world's first controlled gas release field trial to test technologies for the detection of carbon dioxide leaks from Carbon Capture and Storage Facilities, in the sea of Scotland. Not only that, but the passive system accurately quantified the gas flow rate from the leak, continuously over many days, whereas the more expensive system of sending divers down to collect gas in bottle produced a measure of the gas flux only for the short time the divers were down, and so did not pick up the variation of the gas leak rate with tide that the acoustic invention detected. Plans for currently underway for further deployments. Click here for details.

Environmental measures of seabed gas methane: Recommendations from the paper (below) that originally described the system were adopted by European Commission's environmental news service for policy makers (click here for details). It is being trialled by some companies involved in the extraction of natural gas fuel from the seabed.

Leaks from undersea gas pipelines and facilities: The invention has been used by a considerable number of Petrochemical industries for the early detection and quantification of gas leaks – without such technologies, such leaks can lead to devastating effects (as in the 2010 Deepwater Horizon disaster).

For further details, click on the author names below, to go to a web page from where you can request a copy of the paper.

Leighton, T.G. and White, P.R. (2012) Quantification of undersea gas leaks from carbon capture and storage facilities, from pipelines and from methane seeps, by their acoustic emissions, Proceedings of the Royal Society A, 468, 485-510

For more information on bubble acoustics click here .