Company has developed distributed acoustic sensing techniques that can protect pipelines and be used for downhole applications
OptaSense, specialises in distributed acoustic sensing (DAS) for the Oil & Gas sector. The company uses fibre optic cable, conditions the light pulses that go into the fibres, and converts the fibres into a temperature sensor, an acoustic sensor, an electromagnetic sensor, or a pressure sensor.
These applications are particularly useful in Oil & Gas for detecting pipeline leaks, pipeline sabotage, or even detecting the how efficiently a plug is working in fracking.
“All different forms of measurement can be obtained from using a fibre optic cable. The most common forms of distributed sensing are distributed temperature sensing, that has been around for about 15 years and is predominantly used in down-hole markets and in pipelines to look for the temperature effect of efficient operations. When fluid flows out of a hole you get a drop in pressure, and a change in temperature, or when gas expands you get a cooling effect,” said Magnus McEwen-King, MD of OptaSense.
The temperature sensing technology has been around for approximately 15 years and has had moderate adoption rates, according to OptaSense. Approximately seven years ago distributed acoustics was invented and OptaSense pioneered the use of this technology.
“What we found is that there are more applications for acoustic measurements of things than there are of temperature measurements through fibre. So, for example, we can hear the flow of fluid in a pipeline and use it to find injection locations in hydraulic fraction, it is also a geophone replacement.
We can take quantitative seismic measurements exactly as you would with a geophone, but the advantage is now that you do not need a geophone, you can just use the fibre strapped to a well to obtain a seismic image, which means you don’t need to get into the well at all.
A lot of pipeline leak detection systems wait until there is a leak to feel the temperature change to send an alert; either the oil heating the ground, or the gas expanding and cooling the ground. With our leak detection system we are able to hear the car drive up and stop, we can hear someone walking, we can hear someone digging into the pipeline,” said McEwan-King.
In DAS, a box called an Interrogater Unit, which is about the size of a desktop PC, sends a pulse of light down a fibre.
If you shine the same pulse structure identically time after time after time, what you get back is Raleigh Backscatter, which is is the reflection of waves, particles, or signals back to the direction from which they came. In DAS, the same Backscatter will be detected every time, unless there is a disturbance to the fibre.
“We have some clever mathematics in our Interrogator Unit, which is able to unwrap the distortion in the signal such that we have effectively turned the fibre into a microphone and we can hear exactly what is happening with that disturbance in that light pattern,” said McEwan-King.
There are three main parts to the DAS system, the first is the interrogation unit which turns the fibre into an acoustic sensor, second is the way the data is handled.
“One of the curses of DAS is it creates a lot of data, and it all comes down to a how you handle the data. The good news for us is our capability to handle all the real data in real time,” said McEwan-King.
The third piece of the DAS puzzle is the algorithm. Depending on what the DAS system will be used for, OptaSense will load an algorithm into the system.
Article continues on next page …
“If we load a detection algorithm, we are able to detect leaks in pipelines. The algorithm is probably the most important part of the whole system and is how we give our customers decision ready data preset to the customer; the right data in the right format at the right time to make a decision,” said McEwan-King.
OptaSense currently provides pipeline protection to approximately 7% of the world’s Oil & Gas pipelines.
An example of DAS use downhole is that during the fracking process, one of the problems associated with fracking is a plug pass or fail as you bypass from one stage into the second.
“Operators don’t want to have to look at raw data and interpret that to see if the plug passes or fails, they want to know the quantity of fluid bypassing the plug.
If you have two stages with the plug in between if you frack the bottom stage and put a plug in and try and frack the next stage up, you don’t want to put all of your fracking fluid at the bottom, you want, for example 100 units into stage one and 100 into stage 2, but if the plug has failed, some of that fluid that has gone into stage 2 may be flowing past the plug into stage 1.
DAS is able to tell you if that plug is working efficiently so the owner/operator can make an economic decision whether to continue with the fracking stage, or to re-plug it,” said McEwan-King.
