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 H2 or CO2 in the subsurface.
N2 - Plain Language Summary: In the Earth's crust fluid flow can occur in fractured rock and depending on the composition of the fluid and physical conditions minerals can precipitate or dissolve. This affects the properties of the rock system and is for example, of interest to subsurface engineering applications. In this work we simulate observations of laboratory experiments at the grain scale, where crystals grow in an open fracture during fluid flow. In these experiments, the growth rate of the crystals varies along the fracture since the supersaturation of the fluid decreases due to the crystallization. We use a multiphase‐field model for the numerical simulation of crystal growth in the open fracture and combine it with reactive fluid flow. With the presented model the driving force for grain growth is coupled to the local supersaturation, which enables the incorporation of reactive mass transport in open fractures. Our phase‐field simulations agree with the laboratory experiments. The presented simulative approach can be used for upscaling the results on microscale to larger length and time scales and can help to better predict the subsurface behavior for example, of groundwater, fractured geothermal, and hydrocarbon reservoirs. N2 - Key Points:Reactive fluid flow with advective mass transfer causes locally variable precipitation rate in open fracture
A higher flow velocity or a higher supersaturation results in faster precipitation along the flow channel
Phase‐field modeling allows reproduction of laboratory crystal growth experiments from an advecting fluid using transmitted light microscopy