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SENSORS & SENSING SYSTEMS


years of experience developing, deploying and processing data from high pressure and temperature non-electronic all-optical sensor arrays capable of operating at pressures up to 25,000 psi and at temperatures up to 600˚F (~320˚C) in both vertical and horizontal boreholes. After receiving a competitive $1.5 million


grant from the California Energy Commission in partnership with PG&E and Fotech, Paulsson set about designing, building, installing and monitoring a sensor array in the PG&E McDonald Island UGS field. Central to the system is Rayleigh Scattering based interrogation technologies from Fotech using an Enhanced Distributed Acoustic Sensor Array (EDAS) designed by Paulsson. Dr. Björn Paulsson, CEO at the company,


commented: “Fotech is renowned and trusted for its world-leading DAS technology. I knew that its equipment would provide the best possible monitoring and detection for this application. The Fotech DAS system has performed extremely well and has provided robust, reliable and accurate data 24/7 for a period of, thus far, eight months, recording over 400TB of transformative data.” Fotech’s Helios DAS solution essentially


turns a fibre optic cable running alongside horizontal gas pipelines, vertical gas or geothermal wells, into thousands of vibration sensors, able to detect any disturbances along the length of the pipeline or the well casing. The technology sends thousands of pulses of


light along the fibre optic cable every second and monitors the fine pattern of light scattered back. When acoustic or vibrational energy – such as that created by gas flow in the well or in the formation – creates a minute strain on the optical fibre, this changes the back-scattered light pattern. By using advanced algorithms and processing techniques, DAS records these changes to identify and to categorise any disturbance in real-time, thus allowing


immediate processing and interpretation – and if needed – corrective action to be taken. Steve Cammish, chief technology officer at


Fotech, explained: “Each type of disturbance has its own signature and the technology can tell an operator – in real-time – what happened, exactly where it happened and when it happened. What’s more, DAS provides continuous monitoring, 24/7 and over long distances of up to 100km, along pipelines or along and near the deepest wells drilled.”


Detecting gas flow


The solution for PG&E saw a fibre optic cable attached to the 4.5” OD production tubulars, which were lowered down a wellbore inside the 8 5/8” casing for approximately 2km. Using DAS, the array effectively consists of approximately 2,500 sensors, providing accurate real-time monitoring that makes real-time processing, interpretation and action possible. Having this volume of sensors means Paulsson


was able to effectively create a large aperture acoustic antenna so flow in the gas field wells and in the geological formation where the gas is stored, as well as any other events, can be detected and pinpointed to within a metre. DAS has also enabled Paulsson to differentiate between the high permeability sandstone layers and the low permeability shale so a dynamic model of the gas storage field formation can be built. “This is a very exciting step forward for the


technology as we have been able to detect gas flow in a reservoir away from the well for the very first time,” explained Paulsson. “Thanks to DAS’s exceptional accuracy and continuous monitoring capability, it doesn’t just provide us with static data; it allows us to see how the field reacts to the injection of fluids, both gas and liquids, in real- time. This means the data from DAS will allow us to create a 3D image of the ground 1-2km around the borehole, providing complete formation and dynamic flow visibility to our customer PG&E.” Traditionally, geophones spatially separated by


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approximately 15m (50ft), or more, have been used in such applications, but the conditions in boreholes are extremely demanding, with high pressures and high temperatures. Another critical aspect is the need to be able to record the high seismic frequencies found in the sub- surface below the weathering zone. “Using fibre optics and DAS is better suited


to boreholes’ challenging conditions as they can withstand the extreme environment, even at geothermal temperatures. The DAS technology allows for the first-time large arrays of many 1,000s of sensors to be installed, creating large aperture high-frequency sensor antennas with close spatial sensor sampling using the optical technologies,” Paulsson continued.


Visibility


It is not only gas flow that Paulsson has been able to detect and to monitor, but also earthquake events on the other side of the Pacific Ocean in Fukushima, Japan, and in Peru, South America. Paulsson explained: “The sensor array has


picked up acoustic signals from earthquakes over 8,000km away, in Japan and Fiji, which is amazing. Being able to detect other large scale seismic events based on tectonics means we can provide a clear picture of what is happening in the many far and near fault zones in the pacific basin. PG&E is pleased with the results our monitoring solutions have provided.” DAS has wide applications across the oil and


gas industry, including providing advanced monitoring for pipelines. It accurately and reliably detects leaks, and third-party inference such as theft attempts, helping operators to protect the integrity of their assets. Paulsson also has near- term projects to monitor and safeguard gas pipelines and Hydrogen production, transportation and storage using Fotech optical technologies.


Paulsson www.paulsson.com


Fotech www.fotech.com


NOVEMBER 2022 DESIGN SOLUTIONS 13


FEATURE


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