Marie Violay takes ENAC research deeper into the earth's crust

Marie Violay has a deep interest in what goes on in the earth’s crust, several kilometers below the surface. There, fluids and rocks deformed at high pressure and temperature interact mechanically, chemically, and thermally, storing forces that, if perturbed, they could release as earthquakes. A better understanding of how these earthquakes are triggered is crucial for the safe exploitation of the subsurface, be it to extract geothermal heat or to store nuclear waste and carbon dioxide. By combining field observations with laboratory experiments, Violay’s Laboratory for Experimental Rock Mechanics will aim to unravel some of the complex physics that characterizes this largely unexplored environment.

“My research focuses on the mechanical and physical processes in the first kilometers of the earth’s crust,” says Marie Violay, who took on a tenure track professorship at ENAC in July. “Understanding how fluids and rocks interact at these depths is important to develop deep geothermal energy production. Understanding earthquake nucleation and propagation are other important issues: how can we improve our ability to anticipate the likelihood of earthquakes induced by stimulating wells using techniques such as hydro-shearing?”

A major challenge lies in experimentally studying an environment that is all but inaccessible to humans. “Field observations provide plenty of data, but it is difficult to understand the physical mechanisms behind what we observe, in part because the subsurface is highly heterogeneous,” says Violay. “As an experimental scientist, my approach is to study the physics at a small scale using laboratory experiments that replicate the conditions found thousands of meters underground. With the lessons we learn in the lab, we are in a better position to interpret the data that we collect in the field,” she says.

Simulating the subsurface in the lab involves recreating an environment where pressures are measured in mega-Pascals and temperatures in hundreds of degrees Celsius. “Over the next year we will be developing a device capable of deforming small rock samples under pressures and temperatures that are relevant to Swiss geo-engineering projects, as well as to those in more geologically active regions such as New Zealand or Japan,” she says.

While the subsurface long been exploited to extract fossil fuels and build road tunnels, we are still in the early days of recognizing its full potential. Aside from serving as a source of fossil fuels and geothermal heat, it holds the potential to becoming a dependable long-term storage site for nuclear waste and CO2.

These competing uses raise a number of important questions. What, asks Violay, would happen, if geothermal reservoirs were located near nuclear waste repositories? Could seismicity caused by the geothermal reservoirs be transmitted to the geological layers that store the nuclear waste? What are the effects of small perturbations to the stresses exercised underground? She hopes that her research will provide answers.

Violay’s arrival in the faculty coincides with that of Brice Lecampion, an expert in modeling hydraulic fracturing processes who recently joined ENAC as a tenure track professor in geoengineering. Together with Lyesse Laloui and Jean-François Molinari, they will form a new pole of expertise in geo-engineering and geomechanics.