Calibration of water-granite interaction with pressure solution in a flow-through fracture under confining pressure

Fluid-mineral interaction has an irreversible impact on the fracture permeability evolution in the life span of deep geological reservoirs. To investigate the impact, a preliminary study on water-granite interaction in an undeformable fracture under confining pressure is conducted. A 1-D flow and reactive transport model is therefore developed and validated against the experimental data in Yasuhara et al. (Appl Geochem 26(12): 2074-2088, 2011). The model takes free-face dissolution on pore walls as well as enhanced dissolution at asperity contacts into account, together with a nested well-equipped geochemical system. The simulation is implemented by FEM-based simulator OpenGeoSys with a plugin module of IPhreeqc for speciation calculation. After calibration, the predictions of effluent element concentrations are in good agreement with the measurements. The study indicates the high effluent concentrations arise from enhanced mineral dissolution at asperity contacts. Pressure solution at anorthite contacts may not take effect under experimental conditions because of the high-level energy barrier to interpenetration, and Al-bearing secondary minerals such as gibbsite may be formed in the current near-equilibrium aqueous system. The sensitivity analysis suggests that contact area ratio is a paramount parameter in determining the surface reactivity and reactive surface area at contacts.