An experimental study of fracture-induced chemical reactions

Fracturing of rock allows ingress of fluids that may be chemically distinct from native pore fluids. These external fluids can induce dissolution and precipitation, which may be enhanced by highly reactive, comminuted material and metastable highly deformed materials. Reaction products have important feedbacks via dissolution of asperities that affect fracture strength and friction properties. In this study, we examine dynamic fracturing of anhydrite/dolomite using triaxial direct-shear experiments with simultaneous x-ray radiography and tomography. The impermeable cores were fractured at a temperature of 50°C and a confining pressure of 3.5 MPa while being exposed to 500 kPa injection pressure of concentrated (18 wt%) BaCl2 solution. Once fractured, the barium solution invaded the primary shear fracture and the surrounding damaged region. X-ray radiographs and tomography revealed precipitation of barium sulfate and carbonate (barite/witherite). Despite the precipitation, the permeability of the fracture system changed little following the initial fracturing event. Precipitation was likely confined to relatively stagnant flow regions, with more open regions sustaining high flow rates. The experimental results demonstrate laboratory-induced fluid-rock reaction and precipitation in fracture systems and reveal the important role of grain-scale mineralogy and flow pathways on the extent of reaction and the impact of precipitation on permeability.