Micro-Scale Simulation of Fracture Alteration Caused by Coupled Chemical and Mechanical Processes

In this study we present a computational model that couples two previously developed codes to calculate the combined influence of mechanical deformation and chemical alteration of fractures subject to constant normal stress and reactive fluid. Micro-scale roughness of the fracture surfaces is represented explicitly in the model and elastic deformation of the rough surfaces are calculated using a semi-analytical approach that ensures the surfaces remain in static equilibrium throughout the simulations. Chemical alteration of the surfaces is modeled using a depth-averaged reactive transport model, which leads to alteration of the contacting fracture surfaces. The mechanical deformation and chemical alteration calculations are explicitly coupled, which is supported by the disparate timescales required for equilibration of stresses and reactive transport processes. Results show that the transition from transport-limited conditions (low flow rates) to reaction-rate-limited conditions (high flow rates) causes a shift from monotonically increasing permeability to a more complicated process in which permeability initially increases and then decreases as contacting asperities begin to dissolve. These results are qualitatively consistent with a number of experimental observations reported in the literature and suggest the potential importance of the relative magnitude of mass transport and reaction kinetics on the evolution of fracture permeability in fractures.