Human Activities and Earth’s Deep Subsurface Fluid Flow
Human activities have long been known to have a significant impact on the surface of the Earth, with extensive studies conducted on the effects of activities such as greenhouse gas emissions and deforestation. However, researchers from the University of Arizona have now turned their attention to the deep subsurface of the Earth, an area that lies hundreds of meters to several kilometers beneath the surface. Their findings reveal that human activities have a profound impact on the circulation of fluids in this hidden realm.
The study, published in the journal Earth’s Future, focuses on the rates of fluid production associated with oil and gas extraction and compares them to the natural background circulation of water. The researchers discovered that humans have made a considerable impact on the circulation of fluids in the deep subsurface. Grant Ferguson, the lead study author and an adjunct professor in the Department of Hydrology and Atmospheric Sciences at the University of Arizona, emphasizes the importance of providing context to these activities and their environmental impacts.
Impact of Human Activities on Deep Subsurface Fluid Flow
According to the study, human-induced fluid fluxes in the deep subsurface are projected to increase in the future, particularly with strategies proposed as solutions for climate change. These strategies include geologic carbon sequestration, which involves capturing and storing atmospheric carbon dioxide in underground porous rocks; geothermal energy production, which circulates water through hot rocks to generate electricity; and lithium extraction from underground mineral-rich brine for powering electric vehicles.
The research was conducted in collaboration with scientists from the University of Saskatchewan in Canada, Harvard University, Northwestern University, the Korea Institute of Geosciences and Mineral Resources, and Linnaeus University in Sweden. Peter Reiners, a professor in the Department of Geosciences at the University of Arizona and a co-author of the study, emphasizes the importance of responsible management of the subsurface in achieving a green transition and a sustainable future.
Fluid Circulation in the Deep Subsurface
In various processes such as oil and natural gas production, underground water, typically saline, is always present. This water, which is often millions of years old, acquires its salinity through evaporation of ancient seawater or reaction with rocks and minerals. To enhance oil recovery, additional water from near-surface sources is added to the saline water to compensate for the extracted oil and maintain reservoir pressures. The blended saline water is then reinjected into the subsurface, creating a cycle of fluid production and reinjection.
Similar processes occur in lithium extraction, geothermal energy production, and geologic carbon sequestration, where leftover saline water from underground is reinjected. The researchers demonstrate that the rates of fluid injection or recharge from these activities exceed natural rates. By analyzing existing data from multiple sources, including measurements of fluid movements related to oil and gas extraction and water injections for geothermal energy, the team determined that human-induced fluid movement rates are higher than those occurring naturally.
Implications for the Deep Subsurface and Microbial Communities
The study also highlights the potential for human activities to not only alter deep subsurface fluids but also impact the microbial communities that inhabit these environments. As fluids move, changes in water chemistry or the introduction of new microbial communities from the Earth’s surface can alter microbial environments. For example, hydraulic fracturing, a technique used to extract oil and gas by breaking underground rocks with pressurized liquids, can lead to a sudden increase in microbial activity in previously dormant rock formations.
Despite these findings, there are still many unknowns about the deep subsurface and its interactions with human activities. Jennifer McIntosh, a professor in the Department of Hydrology and Atmospheric Sciences at the University of Arizona and the senior author of the study, emphasizes the importance of further research to understand the impact of human activities on the deep subsurface. McIntosh states that utilizing the deep subsurface as part of the solution to the climate crisis is crucial, yet our knowledge of water, rocks, and life deep beneath the Earth’s surface remains limited.
In conclusion, the study conducted by researchers from the University of Arizona sheds light on the significant impact of human activities on the deep subsurface fluid flow. The findings emphasize the need for responsible management of the subsurface and further research to better understand the complex interactions between human activities and the hidden world beneath our feet.
