Phase-Field Simulations of Epitaxial Crystal Growth in Open Fractures With Reactive Lateral Flow

Fluid flow in fracture porosity in the Earth's crust is in general accompanied by crystallization or dissolution depending on the state of saturation. The evolution of the microstructure in turn affects the transport and mechanical properties of the rock, but the understanding of this coupled system is incomplete. Here, we aim to simulate spatio-temporal observations of laboratory experiments at the grain scale (using potash alumn), where crystals grow in a fracture during reactive flow, and show a varying growth rate along the fracture due to saturation differences. We use a multiphase-field modeling approach, where reactive fluid flow and crystal growth is computed and couple the chemical driving force for grain growth to the local saturation state of the fluid. The supersaturation of the fluid is characterized by a concentration field which is advected by fluid flow and in turn affects the crystal growth with anisotropic growth kinetics. The simulations exhibit good agreement with the experimental results, providing the basis for upscaling our results to larger scale computations of combined multi-physical processes in fractured porous media for applications as groundwater protection, geothermal, and hydrocarbon reservoir prediction, water recovery, or storing H-2 or CO2 in the subsurface.