Pressure solution models for quartz materials: Micromechanical development and potential impact in fractured reservoirs

Pressure solution creep is an important contributor to permeability and porosity change in the upper crust. Engineering projects such as enhanced geothermal systems and petroleum extraction are impacted in the short- and long-term by changes in porous and fracture permeability, and are expectedly influenced by similar creep processes. Of currently available models for pressure solution, few are extendable for variable conditions of stress and temperature, and none have successfully constrained final (equilibrium) compaction magnitudes. With past models and experiments primarily focused on granular media, behavior in fractures remains largely untested at pore or reservoir scale. In this work, a micromechanical model is developed for pressure solution creep that maintains complete dependence on aqueous concentrations and is transferable for arbitrary conditions of stress and temperature. Equilibrium compaction is constrained with a form of "critical stress"; dependent on conditions of pore structure and applied effective stress. Compared to laboratory experiments on granular quartz, predictions are accurate across a range of conditions (400-500° C, 20-150 MPa, and mean particle diameter of 3-120ìm). The model is applied to rough fractures to illustrate important feedbacks between elastic deformation and chemical-mechanical creep. Probing analyses of environments typical of enhanced geothermal systems indicate potential importance for pressure solution, particularly following events that disrupt reservoir equilibrium.