Detecting Carbon Sequestration Leaks with Wireless ‘Smart Collar’

A smart collar device could be used to detect leaks from carbon dioxide storage reservoirs by wirelessly communicating with sensor chips embedded in concrete around a borehole and transmitting information back to the surface. Credit: Max Schwaber/Sandia National Laboratories

Geological carbon sequestration, which involves capturing carbon dioxide (CO₂) and storing it deep underground, is an important strategy to help reduce the amount of CO₂ in the atmosphere. In order for carbon sequestration to be successful, the CO₂ must remain trapped underground long term, but methods for detecting leaks can create more paths for escape when wires or fibers are used. Engineers from Sandia National Laboratories are working with scientists from the University of Texas at Austin (UT Austin) to develop a wireless monitoring system that uses “glitter-sized” sensors and a “smart collar” to detect and report CO₂ leaks.

The process of carbon sequestration involves capturing CO₂ from the air or point source, compressing it into a supercritical fluid and pumping it down a borehole under a layer of impermeable cap rock. The areas used to store CO₂ are often depleted oil or gas reservoirs found 3,000 to 12,000 feet below the surface. To detect any CO₂ that may leak from around the borehole, UT Austin researchers created tiny sensors about 3 mm x 3 mm in size that can be embedded in the concrete surrounding the borehole. Chemists from the Research Triangle Institute are currently developing a protective coating that will enable the sensors to withstand the harsh environment of concrete while still allowing CO₂ molecules to reach the sensors.

The Sandia team is developing a wireless device that will power and communicate with the CO₂ sensors that works similarly to radio-frequency identification (RFID) systems that enable the use of “tap-to-pay” credit cards. To design the “smart collar” device, which will surround the borehole, the engineers needed to overcome the challenges of transmitting radio waves through concrete. The intense radio waves needed to charge the sensors can reflect off the concrete, drowning out the waves transmitting information back to the collar. To solve this problem, the team used one frequency to power the sensors, then used less intense waves of a different frequency to query the sensors and receive their data.

The researchers tested a prototype using this method with off-the-shelf RFID chips embedded in one inch of cement and found they were able to successfully power and communicate with the chips. In order for the smart collar to last for several decades underground, supercapacitors are used to store energy rather than traditional batteries. After the collar receives data from the sensors, it can wirelessly report any leaks to operators at the surface.

“There’s way too much CO₂ in the atmosphere right now and it’s only getting worse,” said Alfred Cochrane, a Sandia electrical engineer working on the project. “Along with all the other technologies like renewable energy, carbon sequestration is an active approach to mitigating climate change. If you capture carbon from a coal-fired power plant or a cement plant and store it indefinitely, you could make those processes carbon neutral or even allow us to go carbon negative and remove more CO₂ than we emit.”

Later next year, the Sandia and UT Austin teams plan to demonstrate the full smart collar and sensor system together, first at Sandia’s above-ground testing facility and then at UT Austin’s underground test facility. The researchers say the technology could also be used to monitor storage areas for natural gas or hydrogen leaks, in addition to carbon sequestration applications.