In Situ Investigation of Fluid‐Rock Interactions at Ångstrom Resolution

Abstract

AbstractThe flow of aqueous phases through porous media shapes the world. It changes the courses of rivers, erodes mountainsides, dissolves historical monuments, builds caves, regulates the carbon cycle, and changes porosity in aquifers and hydrocarbon reservoirs. Despite the significance of this process both to natural phenomena and human endeavors, fundamental insight into the mechanisms that drive it at the Ångstrom scale is scarce. Here, we employ environmental transmission electron microscopy (ETEM) to visualize interactions between water and various types of porous media, including sandstone, limestone, and dolostone samples, at Ångstrom resolution in real time. Unlike other techniques presented in the literature, ETEM allows for direct visualization of both the aqueous phase and the porous media. As expected, dissolution and recrystallization were observed to significantly impact the shapes, sizes, and interconnectivities of the pores in the rocks. However, for the first time, we provide direct in situ experimental evidence that adsorption‐induced strain can also significantly impact the above‐mentioned parameters, especially in micropores. In some cases, adsorption was observed to reduce effective pore size by more than 60%. The magnitude of the change in pore size was found to vary with pore wall mineralogy and pore geometry. This work presents the first direct Ångstrom‐resolution observations of liquid adsorption films and adsorption‐induced strain.