Permeability, alteration, and microstructure: A (hopefully) coupled rock physics and geochemical approach to how rock-fluid interactions change permeability

Permeability is a key physical property across all spatial scales in the Earth’s crust and exerts significant control on the behaviour of Earth systems, with implications for natural hazards (e.g., earthquakes, slope instabilities, volcanic eruptions) and geo-resource management (e.g., geothermal energy, carbon capture and sequestration, ore deposit formation). Amongst other processes, rock-fluid interactions and the interplay between precipitation and dissolution complicates the microstructure of these materials, modifying the efficiency of fluid flow. For example, the permeability of volcanic rocks is generally controlled by the presence of pores and microfractures, but the continuum from pore-dominated to microfracture-dominated permeability is significantly perturbed by the introduction of alteration minerals that reduce the void space available to fluid flow over time. The propensity, extent, and timescales of rock alteration are therefore important factors influencing rock permeability. However, obtaining a systematic understanding of the intricate relationships between rock alteration and changes in permeability – including dissolution, transport, and redistribution of chemical compounds – is challenging. As a result, we do not fully understand how these processes modify the structure of permeable channels and over what timescales they may hamper fluid flow, limiting our ability to effectively model, for example, geothermal reservoirs or volcanic processes. The mission of the new Rock Physics and Geofluids (RPGL) group at EPFL is to address how secondary mineral precipitation – starting with silica (SiO2) - changes the permeability of rocks. Using a mix of rock physics, microstructural and geochemical characterization, and water-rock interaction experiments, we will quantify 1) the physical and chemical conditions promoting silica alteration under a wide range of crustal conditions, 2) how the geometry of fluid-flow pathways in rocks changes over time, 3) how these changes modify permeable flow, and 4) on what timescales these processes are active. Our goal is to establish the infrastructural, experimental, and analytical foundation needed to more broadly study the relationships between rock-fluid interactions and fluid flow, for potential application to natural hazard and geo-energy research.