As one of the Department of Energy’s (DOE) national laboratories, Lawrence Berkeley National Lab is tasked with solving some of the country’s most challenging energy-related challenges. One of the greatest geoscience challenges facing society is how to move away from fossil fuels for energy to reduce the nation’s carbon footprint.
With this aim in mind, a team of geophysicists led by Véronica Rodriguez Tribaldos of Berkeley Lab and Jonathan Ajo-Franklin of Rice University set out to find a clean alternative energy source in the form of geothermal energy – natural reservoirs of hot water deep in the earth. Some geothermal resources can be easy to spot from the surface – hot springs and geysers in places like Yellowstone National Park are key indicators of the wealth of geothermal energy lying beneath the surface.
Often, however, valuable geothermal resources are not so obvious. The United States Geological Survey (USGS) estimates that there are several gigawatts of hidden geothermal resources waiting to be tapped and turned into energy.
The Hunt for Hidden Geothermal Treasures
The challenge, then, becomes finding these hidden geothermal resources and mapping them out. Only then can scientists begin to unlock their potential.
For this research project, the Rice-Berkeley Lab team, in collaboration with other scientists from Lawrence Livermore National Lab and Scripps Institution of Oceanography, focused their attention on the Imperial Valley in California, at a site just south of the Salton Sea and close to the U.S.-Mexico border. First targeted by oil and gas companies who found hot water instead of the fossil fuels they were seeking, this region is now renowned for its vast pool of geothermal resources.
Unlike the Salton Sea field that features geysers, bubbling mud pits, and mud volcanoes – sure signs of geothermal activity underground – the Brawley Geothermal Field where Berkeley Lab focused its attention lacked surface expression. Geophysicists knew that there were geothermal resources underground in the Brawley field – thanks to previous exploration by oil and gas companies – and wanted to investigate the seismic signature of this previously hidden system. With the knowledge gained from the Brawley field research, the team could then apply the same techniques to find hidden geothermal resources.
Revolutionizing Seismic Data Collection with Dark Fiber and DAS
To investigate the field, researchers had a few options: First, they could deploy traditional seismic sensors every few meters in the area – something that takes extensive time, labor, and money. Doing this type of project involves permits with long approval wait times, large teams and budgets, and lots of manual labor.
These factors made option two more attractive to the team. Instead of deploying sensors individually, they could tap into a local resource already in the ground but being used for something else – dark fiber. This is the part of the story where Zayo comes in.
Aside from its initially intended purposes, unlit telecom fiber can be turned into thousands of seismic sensors using a technique called Distributed Acoustic Sensing (DAS). These sensors measure ambient noise or earthquake waves bouncing around the earth as a function of time, giving scientists a better picture of what lies underneath.
Because this asset is already in the ground, all scientists must do to tap into it is go to the point of presence (PoP) and install an interrogator – a device that listens to signals sent through fiber optic cables, enabling scientists to detect seismic activity. This significantly reduces the project’s cost and the time that would otherwise be required to get the proper permits to place sensors and then do the work to place them.
In just two days, the team was able to use DAS to highlight where the geothermal resource was by detecting specific seismic signatures indicative of geothermal activity. This is a conclusion that may have taken months to reach without DAS. Zayo happened to have dark fiber at the right place and time for the team to better understand previously hidden geothermal resources in the Imperial Valley.
Ajo-Franklin of Rice said that the time savings made possible by using pre-existing fiber infrastructure significantly benefitted the team’s research. Ajo-Franklin also noted the importance of Zayo’s expertise in the project, “This isn’t a typical telecom project; it requires equipment with capabilities that other projects do not have, and technical guidance to support our team in making decisions relevant to deploying the fiber.”
Because of this research, scientists now have an efficient way of finding previously unknown, untapped geothermal resources that could help lower fossil fuel emissions by providing a low-carbon, reliable, alternative source of energy. This alternative improves local air quality and enhances energy security while aiding in reaching carbon offset goals. Geothermal energy is emerging as a vital component of the movement to cleaner and more sustainable energy systems.
The Many Applications of DAS – Now and in the Future
Leveraging dark fiber and DAS to find hidden geothermal resources is just the tip of the iceberg – this type of research can have many applications. DAS is revolutionizing the world of seismic sensing and providing opportunities for cleaner energy, better natural disaster detection, and smarter cities.
Using DAS data, scientists can create 3D maps of Earth’s subsurface, enabling a variety of applications. These applications include geothermal exploration, monitoring changes in rock formations due to CO2 injection, and studying the water cycle by monitoring aquifers and their responses to stress.
This technique also allows for high-resolution earthquake monitoring, giving scientists a better understanding of faults and their behavior and detecting earthquake early warning signs, possibly giving cities a few-second head start to shut down critical infrastructure and improve safety before an earthquake strikes.
Aside from applications on terrestrial fibers, DAS on marine fibers can open up brand-new opportunities. This technique applied to subsea cables can help scientists study mammals like whales, monitor mudslides, and understand water column dynamics.
What’s more, DAS isn’t just useful to scientists – it can help telecom operators, too. By monitoring vibrations along fiber optic cables, telecom providers can detect tampering or damage.
The future for DAS looks bright. DAS technology has the potential to generate rich datasets that could be valuable for a number of different uses. Urban planners, geophysicists, and transportation operators could use these datasets for a wide range of applications. For example, data could be used for smart city applications, enabling urban planners to gather insight on metrics like traffic volumes on highways.
Ultimately, the goal is to not only use this data but also process it in near real-time, allowing for quicker response to events. Getting information as close to real-time as possible can enhance earthquake detection and early warning systems, reducing response times even further.
Overall, the use of dark fiber and DAS technology has far-reaching implications for humanity. This research enables cleaner energy through geothermal exploration, bolsters natural disaster detection, and contributes to smarter cities by enabling the creation of 3D subsurface maps. This technology holds the potential to allow scientists to explore marine life, mudslides, earthquakes, and water dynamics. As scientists strive for real-time processing of critical DAS data, this technology promises to provide even further innovation and insight.
Note: The research at the Lawrence Berkeley National Lab was funded by the Geothermal Technologies Office, part of the Office of Energy Efficiency and Renewable Energy (EERE) under the Department of Energy (DOE). The DOE does not endorse any specific technologies or companies.