Abstract Subcritical crack propagation in stressed carbonate rocks in a chemically reactive environment is a fundamental mechanism underlying many geomechanical processes frequently encountered in the engineering of geo-energy, including unconventional shale gas, geothermal energy, carbon sequestration and utilization. How a macroscopic Mode I crack propagates driven by a reactive fluid pressurizing on the crack surfaces with acidic agents diffusing into the rock matrix remains an open question. Here, the carbonate rock is modeled as an elasto-viscoplastic material with the mineral mass removal process affecting the rock properties in both elastic and plastic domains. A blunt-tip crack is considered to avoid any geometrically induced singularity problem and to allow a numerical analysis on the evolution of the chemical field being linked to the micro-cracking activities in front of the crack tip, affecting the delivery of acid. The model is capable of reproducing an archetypal three-region behavior of subcritical crack growth in a reactive environment. The crack propagation exhibits a prominent acceleration in Region III due to a two-way mutually enhancing feedback between mineral dissolution and the degradation process, which is most pronounced in front of the crack tip. With the consideration of initial imperfections in the rock, the macroscopic crack propagation is further accelerated with a secondary acceleration arising due to self-organization of micro-bands inside the chemically enabled plasticity zone.
A recent trend in improving the seismic safety and economic efficiency of enhanced geothermal systems in deep rock formation has led to an interest in the underlying mechanisms of shear stimulation. This contribution investigates the formation of shear localization patterns around an injection hole in deep geothermal reservoirs considering thermo-hydro-mechanical coupled processes. The constitutive formulation treats the target rock layer as an elasto-visco-plastic material with an Arrhenius dependence taking into account the effect of pore fluid pressure. Considering the thermal pressurization effect resulting from frictional heating, the role of system heterogeneity and the influence of injected fluid temperature are investigated. The findings of this study indicate that a deeper layer and a hotter injection would favor localized shear deformation around a deep borehole and hence an effective network of fluid pathways.
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