Circular energy

Elaine Maslin reports on a new solution aimed at converting heat in subsea pipes into power, and then using that power to measure what’s going through those pipes.

Hot Ring. Image from Exnics.

“Hot Rings” firm Exnics has its sight set on further offshore trials of its subsea power system after identifying how it could improve output of the system by 60%.

The firm is also developing non-intrusive instrumentation, to be powered by its hot rings technology, which could improve production rates by monitoring flow regimes inside flowlines. The technology would move the firm towards becoming a data services firm, providing insight for operators to optimize flow rates on their fields, in both green and brownfield environments.

The firm, based in Aberdeenshire, had the first trial of its hot ring technology last year on EnQuest’s Crathes subsea tieback in the North Sea. The technology is a thermal energy regeneration system, based on rings, fitted with thermoelectric generators (TEGs), which can be clamped around production flowlines. The heat inside the pipe is converted to electricity, which recharges batteries used to power instrumentation.

Stuart Ellison, the firm’s director, says learnings from the six-week trial last year, as well as work with Heriot-Watt University in Edinburgh, via the Oil and Gas Innovation Centre, on nano-engineering, has improved the TEGs in the firm’s rings, enabling up to 60% increased power output, i.e. from 10w, from a 100°C, production flowline, to 16w, per ring. To generate more power, more rings can be added at a rate of six rings per meter to cover various power needs.

The Hot Rings deployed in last year’s North Sea field trial used off the shelf TEGs. These commercially available TEGs are designed to cover a wide range of industrial uses and therefore have a broad range of operational temperatures. Subsea flowlines have a much more defined temperature envelope. By taking control of the TEG design, Exnics has developed a TEG specifically for the subsea flowline application, which is, therefore, much more effective than an off the shelf TEG. It also meant they could determine the geometry of the TEGs and make better use of the available space while also improving the build quality.

In December, the firm won approximately US$200,000 (£150,000) in funding to develop a brownfield version of the Hot Ring technology. This has been dubbed the Talon, as the semicircular Hot Ring components are used as fingers to form a three-fingered claw shape which is installed around a pipe. It could be diver or ROV deployable providing a continuous power supply for an instrument package.

Using the remote power package, Exnics is developing a non-intrusive flow monitoring system based on measuring minute optical variance on the surface of a pipe using a laser and then putting the signal through a machine learning process, patent pending. By doing this, they say they are able determine fluid properties and flow parameters within the pipe.

The firm is working on a project with the Oil & Gas Technology Centre in Aberdeen to develop the technology with the aim of gaining better visibility of commingling fluids in subsea manifolds. Over 500,000 boe/d are commingled blindly in subsea manifolds on UKCS alone.

Initially, Exnics plans to pilot the technology in onshore terminals where pipelines make landfall, using a portable, tripod-mounted system. The firm can use the data collected from the pilots to further train their algorithm ahead of offshore and ultimately subsea trials.

The firm’s goal is to develop a monitoring system which the Hot Rings could power under an “edge analytics” philosophy, i.e. where a certain amount of the processing is done at the instrument, so that only the information that is required has to be transmitted, potentially acoustically, where there’s no communication system in place to tap into. Not sending all the data would also reduce how much power is needed for transmitting data. The data sent could help platform operators tune the choke setting, gas lift and ESP drive frequency of individual wells in subsea clusters, to help prevent certain wells backing out others, on a field by field basis, for example. The data could then also be used more broadly across a business to track trends such as predicting sand ingress or water cuts, says Ellison.