Science & Technology: New Research on How Geothermal Fluids Flow Through Fractures

Understanding Anomalous Transport in Fractured Rock (MIT Earth Resources Laboratory)

New work from MIT Earth Resources Laboratory deepens understanding of fluid diffusion through networks of tiny cracks in subsurface rock.

To fully understand the risks and benefits of underground activities such as oil/gas production, geothermal energy production, or carbon sequestration, energy industry scientists need a detailed understanding of how fluids flow through fractures deep beneath the Earth’s surface. Contaminants or other tracers in fluids such as water can diffuse through porous rock following a pattern similar to diffusion in other materials—a process called Fickian diffusion—but when the rock contains a network of fractures, the process may become more complex. The interplay between the fracture geometry and the fluid velocity can speed up or slow down diffusion, in the form of “anomalous transport”.

ERL Researchers Peter Kang, Stephen Brown, and Ruben Juanes found that standard diffusion in a rough-walled fracture can transition to anomalous transport at higher stress, as the fluid organizes itself into channels and no-flow zones, causing both early arrival and long residence times of contaminants. In a 2016 paper in Earth and Planetary Science Letters, they proposed a new model that explains both types of diffusion and quantitatively describes the transition between them in a single fracture. In a new paper in Water Resources Research, Kang, Juanes and co-workers extend their analysis to a network of fractures, and applied it to a real fracture network from a natural outcrop.

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Stress‐induced Anomalous Transport in Natural Fracture Networks, by Peter K. Kang, et al. First published: 17 April 2019. Water Resources Research https://doi.org/10.1029/2019WR024944