As the world battles climate change, a new system created by researchers in Japan could help scientists in the fight.
The method, developed by a team at Kyushu University, provides accurate and frequent measurements of changes below the Earth’s surface, which they say could lead to implementation of corrective actions such as carbon storage and geothermal energy generation. And, thanks to a small seismic source and fiber-optic cables, it allows continuous monitoring of the ecosystem underneath (see figure).1
“Storing captured carbon dioxide underground and generating electricity from geothermal energy are two important technologies for reducing greenhouse gases,” says Takeshi Tsuji, a professor at Kyushu and lead author of the study.
Small seismic sources that generate accurately timed vibrations over a wide range of frequencies are used in the new monitoring system, in which a 17 kg off-centered weight rotates, creating vibrations that allow the ground to be probed. Those vibrations and seismic signals, which can be stacked to improve signal-to-noise ratio, are then detected through distributed acoustic sensing at hundreds of points along a fiber-optic cable that can be as many as tens of kilometers in length; the changes are measured by the light passing through the fibers.
According to the study, the researchers were able to identify changes in the pressure of fluids within voids in the ground (called pore pressure). The team notes that changes “could indicate hazards such as leakage of carbon dioxide or changes in geothermal reservoir.” Testing the new system’s effectiveness via field experiments also identified changes in subsurface formation signals with greater than 99.99% accuracy.
Tsuji notes that to further adopt tools such as underground carbon dioxide storage and electricity generation from geothermal energy, better monitoring tools will be key “to mitigate and respond to related risks such as leakage and induced earthquake activity.”
According to the researchers, their monitoring system could also be combined with traditional seismometers and autonomous surface vehicles. Such vehicles produce acoustic waves offshore, which could expand the monitored region.
Vibration and seismic monitoring has historically been done in extended time intervals due to the high costs associated with it, causing a gap between all of the data that’s collected. As a result, it can be too easy to miss any rapid and/or unexpected changes in carbon dioxide levels or geothermal reservoirs. The Kyushu team’s new system and technique are not only more effective at monitoring and identifying potentially crucial changes, they also are much less expensive than existing methods.
“By giving us the means to detect and respond more quickly to leaks and other hazards,” Tsuji says, “the continuous monitoring our system enables will also help in gaining the public acceptance that is vital for advancing carbon capture and storage and geothermal energy development projects.”
1. T. Tsuji et al., Sci. Rep., 11, 19120 (2021); doi:10.1038/s41598-021-97881-5.