Carbon Underground

Berkeley Lab’s Seismic-Based Technology Offers More Sensitive, Near Real-Time Carbon Dioxide Storage Measurements

Amidst the farmland near Australia’s coastal town of Warrnambool rests a grassy field whose flatness is interrupted by a prefab house and fenced-off areas containing well heads poking from the ground. Smaller areas of fencing surrounding bright orange devices on concrete pads also lie throughout the remote facility located along the country’s southeastern coast. 

The site known as the Otway Project has become a research center for determining how best to inject and safely store carbon dioxide underground. For the past decade, EESA scientists have been collaborating with the Australian research institution CO2CRC, which manages the site, and Curtin University to test new methods for monitoring CO 2  migration. The EESA team deployed nine of the bright orange surface orbital vibrators (SOVs) mounted on heavy concrete pads. These small, autonomously operating machines generate specific vibration patterns (also referred to as seismic signals) that can be used to measure carbon dioxide behavior underground in near real time. 

Such persistent seismic monitoring is critical to ramping up the use of geological carbon storage (GCS) technologies that are considered an important strategy to achieve carbon neutrality over the next few decades before the use of fossil fuels is phased out. Jens Birkholzer, director of the Energy Geosciences Division at Berkeley Lab, said, “GCS is essential not only for storing CO 2  captured from large emitters such as power plants and industrial complexes, but also to sequester carbon that is scrubbed back out of the atmosphere in a novel process called Direct Air Capture." 

Monitoring technologies such as the bright orange SOVs at Otway are particularly useful since there’s always a small chance the carbon dioxide could move along pathways in subsurface rock and upward into nearby aquifers or toward Earth’s surface. So far at Otway, the SOVs custom built at Berkeley Lab’s  Geosciences Measurement Facility  have provided snapshots of the CO 2  in Earth’s subsurface every two days since early 2020 when it was first set-up for continuous operation, according to Berkeley Lab Research Scientists Julia Correa and Stanislav Glubokovskikh. The ability to acquire this near real-time information could become relevant for other teams elsewhere needing to respond rapidly to any safety concerns at future, long-term GCS sites.

“GCS is essential not only for storing CO 2  captured from large emitters such as power plants and industrial complexes, but also to sequester carbon that is scrubbed back out of the atmosphere in a novel process called Direct Air Capture."–Jens Birkholzer, Energy Geosciences Division Director

EESA scientists have a long history of developing new approaches to monitoring CO 2  migration underground, with the Otway project being one of the longest-running examples. In addition to smart-sensing technologies, EESA has fast tracked a range of other important geoscience capabilities, such as making computer modeling predictions to ensure that injecting would not cause earthquakes or exploring ways to enhance CO 2  trapping via  chemical reaction with surface rocks .


Testing Enhanced Seismic Technologies

During the first few years of the Otway Project, collaborators from Curtin University in Australia, who lead the geophysical monitoring program at Otway, used more traditional technologies for interrogating CO 2  migration. Among them were trucks the size of fire engines capable of producing vibration signals that, when reflected, can image a CO 2  plume on the scale of meters. Seismic monitoring conducted until spring 2018 demonstrated successfully that a CO 2  volume as small as 5,000 metric tons can be detected deep underground with the conventional monitoring approach.

At Berkeley Lab's Geosciences Measurement Facility, Engineering Associate Todd Wood helped design, build, and deploy some of the technologies used in the Otway project.

However, seismic surveys conducted with such vibroseis trucks are very expensive and quite slow in contrast to SOVs that can provide seismic snapshots as often as every two days. So when the third stage of CO 2  monitoring started at Otway, Correa, an EESA scientist with the Energy Geosciences Division, Engineering Associate Todd Wood, and some of their university colleagues in Australia, visited Otway and installed the more advanced SOV monitoring equipment, which requires a smaller footprint and can acquire a seismic survey autonomously in near real time, a major improvement from the conventional technology. 

“By fixing the sources’ location,” Correa said, “you eliminate one of the biggest issues with data variability in time-lapse seismic, greatly improving your ability to rely on the signal produced to reveal the distribution of the CO 2  that’s been injected.” –Energy Geosciences Division Research Scientist Julia Correa

The SOVs, which resulted from years of previous research by retired EESA researcher Barry Freifeld, have motors that can generate a signal force of five to 20 tons. Acoustic waves they generate propagate underground, where echoes are produced and recorded by fiber optic cables installed inside five deep boreholes throughout the Otway storage site. 

The SOV measurements revealed remarkable details of the CO 2  saturation at Otway after 15,000 metric tons of CO 2  was injected into the underground between December 2020 and March 2021. The team’s analysis showed that the vibrators and associated fiber-optic sensors could detect small leakage volumes of as little as 580 metric tons of injected CO 2 . A major reason for the high data quality is that each SOV is permanently fixed to its location on the surface, reducing the data reproducibility challenge of vibroseis trucks. “By fixing the sources’ location,” Correa said, “you eliminate one of the biggest issues with data variability in time-lapse seismic, greatly improving your ability to rely on the signal produced to reveal the distribution of the CO 2  that’s been injected.” 

Fiber-optic cables, such as those photographed above at another project location, are installed inside five deep boreholes throughout the Otway storage site. The sensors and associated SOVs are capable of distributed acoustic sensing (DAS), and the team's analysis has shown the pair could detect small leakage volumes of as little as 580 metric tons of injected CO2.

Rapid Processing and Remote Operation

SOVs have a huge advantage over using traditional technologies, namely because they can be operated remotely from any location regardless of the distance from the project site.

The SOVs and associated fiber-optic sensors capable of distributed acoustic sensing (DAS) also have the advantage that data processing can be standardized to produce near-continuous, automated data products created using the data acquired in the field. The Otway monitoring data is made accessible online by Curtin University researchers and can be processed to allow for rapid plume detection. By comparison, vibroseis truck data can take days to months to become available at survey’s end, and traditional processing may take another few months. As a result, detection of a CO 2  leakage event with traditional surveys could take a very long time. 

The SOVs installed by EESA researchers can be operated remotely, which became crucial when Australia went into lockdown mode due to COVID-19 soon after the equipment installation was completed in March 2020. Correa pointed to the advantage of remote operation. Study data from Otway “has continuously arrived on our computers for over two years now” without the need for collaborators as far away as Berkeley having to travel to the field site.” She added, "By having continuous sensors like this in future GCS projects, we can improve the safety of carbon capture and storage by providing more frequent snapshots of a CO 2  plume's underground location, while simultaneously monitoring any critical leakage or earthquake events."

At Berkeley Lab's Geosciences Measurement Facility, Engineering Associate Todd Wood helped design, build, and deploy some of the technologies used in the Otway project.

SOVs have a huge advantage over using traditional technologies, namely because they can be operated remotely from any location regardless of the distance from the project site.