Understanding Anomalous Transport in Fractured Rock

Joshua Kastorf | MIT Earth Resources Laboratory
Friday, April 19, 2019

New work from ERL deepens understanding of fluid diffusion through networks of tiny cracks in subsurface rock.

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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 members -- Peter Kang, who is an MIT research affiliate; Stephen Brown, a research scientist in the MIT Department of Earth, Atmospheric and Planetary Sciences (EAPS); and Ruben Juanes, ARCO Associate Professor in Energy Studies in EAPS and MIT's Civil and Environmental Engineering -- 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 their colleagues extend their analysis to a network of fractures, and applied it to a real fracture network from a natural outcrop.

The 2019 study was funded by the Korean Ministry of Environment (grant W12530(2018002440003)), the European Research Council (ERC project MHetScale (617511)), and by the U.S. Department of Energy Office of Science (grant DE-SC0018357). The 2016 study was funded by the U.S. Department of Energy through a DOE CAREER Award (grant DE-SC0003907), a DOE Mathematical Multifaceted Integrated Capability Center (grant DE- SC0009286), and the Korean Ministry of Land, Infrastructure and Transport (grant 16AWMP- B066761-04). The MIT Earth Resources Laboratory is funded, in part, by our Founding Members.

Story Image: Kang et al 2019. (Credit: courtesy of the authors)