Molecular Dynamics Simulation Prediction of Clay Swelling as a Function of Aqueous Chemistry

Abstract:

A recurrent theme in the use of the subsurface for water, energy, or carbon mitigation is the importance of fine-grained (clay-rich) soils and sedimentary rocks. Fine-grained rocks (shale, mudstone) are used as caprocks, host rocks, and source rocks in a range of low-carbon energy technologies including carbon capture and storage, high-level radioactive waste storage, and shale hydrocarbon extraction. Fine-grained soils play an equally outsized role in agriculture and soil carbon storage. This importance of clay-rich media derives largely from their distinct hydrologic and mechanical properties (ultra-low permeability, swelling-shrinking and cracking). Here, we present recent molecular dynamics simulation predictions that shed light into the swelling mechanics of swelling clay (smectite) and its dependence on aqueous chemistry (salinity, counterion type, and water chemical potential). In particular, we show that all-atom MD simulations can provide insight into the transition between the short-range ‘crystalline’ swelling and the long-range ‘osmotic’ swelling observed for smectite clay.