In carbon capture and storage (CCS), carbon dioxide is removed from emissions, pressurized into a ‘supercritical fluid’, and then pumped deep underground into porous rock reservoirs, where it theoretically remains trapped. Potential carbon storage sites include depleted oil and gas fields and deep saline aquifers.
Although CCS technology has been around for decades, it has yet to become widespread. That’s partly because of the high cost of building sequestration facilities, but also because of how well the process actually works. Over long periods of time, even a small amount of carbon dioxide leakage can become significant, and where storage sites lie beneath the sea floor, a leak can have profound effects on marine life.
Just finding leaks is difficult and expensive. CCS monitoring typically relies on heavy seismic equipment mounted on trucks or ships. The device sends strong vibrations into the earth’s crust and analyzes the sound waves that are reflected back.
Due to the high cost, such systems can only be used for limited periods of time. “In a traditional system, monitoring is discontinuous,” said Takeshi Tsuji, an engineering professor at the University of Tokyo. “It’s difficult to collect seismic data continuously.”
However, Japan’s ambition to explore the solar system may have led to a breakthrough in carbon storage here on Earth. A team from the University of Tokyo and Kyushu University, led by Tsuji, has developed a lightweight system, the Portable Active Seismic Source (PASS), designed to be carried aboard Mars and Lunar landers and may also detect carbon leaks at sequestration sites . Scientists published their results in Seismological Research Letters Last month.
Just 10 centimeters long, the PASS generates vibrations through a spinning wheel mounted with an off-center weight. Because of the device’s small size, the vibrations it produces are relatively weak, but the team uses software to ‘stack’ hundreds of signals, greatly amplifying the transmission.
The stacked seismic signals can penetrate more than 800 meters underground. CCS wells must be deep enough to keep carbon dioxide under pressure. In theory, arrays of PASS boxes could be placed over these sites, allowing geologists to monitor carbon leakage. “This system is very cheap,” Tsuji said, “and it generates continuously, so we’ll be able to monitor continuously.”
PASS boxes could help Japan meet its ambitious goal of being carbon neutral by 2050. As part of that goal, the country plans to capture up to 240 million tons of carbon dioxide per year in hundreds of wells, mostly offshore.
Toru Sano is a Geophysicist at JX Nippon Oil & Gas Exploration, a Japanese company planning to incorporate CCS into its operations. He said the PASS’s small size and low cost make it ideal for long-term surveillance of sequestration sites. “We not only need to monitor the injection period,” he said, “but also after the site is closed — for maybe 10, 20 or even 50 years.” Continuous monitoring is also important to improve public perception of site safety to control CO2 capture.
Although some critics have accused Japan of pursuing carbon storage as a way to continue extracting and burning fossil fuels while meeting its net-zero carbon goals, the United Nations Intergovernmental Panel on Climate Change believes CCS is crucial to the global to limit warming. According to the latest climate change report, there are more than enough potential carbon sinks on Earth to store all the carbon dioxide needed to limit warming to 1.5C, but current deployment of the technology is well below what is required to achieve this goal.
– Bill Morris, science writer