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Fibre optics to listen to your wells

Friday, June 10, 2011 in Feature Articles

Standard fibre optic cables can be used as an acoustic sensor without any discreet components along the length of the fibre. This can be useful in oil and gas wells, for example if you want to know at which point oil, gas, water or sand is entering your well, says Doug Gibson, CEO of Fotech Solutions

Fibre optic cable is very clever stuff. If a cable is excited by a sound wave, some of the light travelling through the fibre experiences a phase change which when analysed in real-time by Fotech’s Helios system outputs acoustic information reproducing the original sound wave. This information is available for every metre along a fibre optic cable for distances greater than 50Km.

“If I were to lay a fibre between central London and Heathrow airport, and you walked to Heathrow airport, I could follow you to the airport and position you to 1 metre accuracy,” said Fotech CEO Doug Gibson, speaking at the March 16 Finding Petroleum London forum. “You can have the equivalent of microphones every metre along the fibre.”

So if you have fibre installed inside your wells, you can find out a lot of useful information and enhance your understanding of your well’s performance. This is the only tool that will give you a top to toe real-time view of your well’s dynamics.

For example, one client installed fibre in a tight gas well with 9 fractured zones. The client thought that the rock was homogenous and production would come from all 9 zones. But the fibre optics could only hear noise from two of the zones and from the bend in the pipeline (caused by vibration in the tubing) – suggesting that production was only coming from 2 of the 9 zones. Although the fibre was not all the way into the well, careful analysis of the acoustic data helped us interpret that statement.

“A well which the oil company thought would produce all the way along the wellbore, is actually only producing from this one area here in zone 7 and potentially a small amount in zone 9,” says Doug Gibson, CEO of Fotech Solutions, a company developing the technology.

“This is just by listening to the fibre that has been installed either temporarily or permanently in the well.”

You can also get a much better understanding of what happens when a well is shut in.

In one example, after shutting a well in, a client could see the water column in the well gradually falling down the well, but meanwhile still see gas continuing to rise up through the well.

When the well was brought up to production again, you could see water coming out of one of the zones, and faster gas starting to slug out of the zone It takes a while for production he zones to come back but meanwhile you can pinpoint the producing layer within the zone.

Another client had a problem with sand production in a well, but didn’t know which point in the well the sand was entering. The fibre optics can be used to show where the sand was entering. Although unable to show the data publicly, Fotech were able to show to a metre accuracy, where the sand was breaking through the sand screen, allowing the oil company to rework the well and shut off the sand.

In another example, with a well with uncemented casing above a certain point, you can see leaks of fluid coming into the well at the casing interface. “We’re showing them there’s a leak in their casing system,” he said.

“You can see movement which has never been seen as far as I know by any other technology,” he said.

“I think you’ll see that here is a technology that allows you to do an awful lot more to understand the dynamics within the wellbore and in real-time.”

“You can listen to different things going on in the well, you can listen to leaks, flow, moving sleeves, valves, pumps, microfracturing, microseismic, etc.”

The system could help make fracturing much more efficient. If people know which fractured zones are producing and which ones aren’t, they can see which zones to focus on in future. “The cost of fraccing is tremendously high,” he said. “We can tell the client in his quest to understand what’s worth producing and what’s not.”

The system could also be used in carbon dioxide storage, if you want to see which zones of your reservoir the gas is going into. You can also track the flow of gas through the rest of the pipeline for leaks, turbulence and friction.

It is possible that in the future the system could be used to analyse 3 phase flow but this will take time and a lot of research I suspect.

“It’s in its early days – we hope to come back soon with a lot more case histories to show you.”

The system can also be used for other applications, including security, or following things (you could have fibre laid along a road, and follow a car along a road from the noise it made).

The system uses standard fibre optic cable, but some very clever processing at the surface. It can provide data to 1m accuracy, along a distance of 50km.

The fibre sensor is not yet as sensitive as a geophone or accelerometer in detecting noise, “but we’re getting better and better,” he said.

All of the electronics are at the surface.

Fibre is installed in production wells using wireline, or with a hard carbon rod or permanently on tubing or outside casing. “The fibre is just simple fibre – it costs nothing when compared to current downhole sensors,” he says. “The cost you’ll come up against is the cost of installing this into the well.”

The technology was originally developed by researchers at Imperial College and later Surrey Technology, who started a spin-off company in 2008. Fotech shareholders include Scottish Energy Partners, Energy Ventures and Shoaibi Group (Saudi Arabia).

In the market, “I think the general opinion is bemusement at the moment, nobody can quite believe what it can do,” Mr Gibson said. The reality is this is the first technology that can produce a real time continuous view of the entire well allowing a ”video” of the well performance and the ability to change production parameters and watch the effect.