Impact of mineral composition and distribution on the mechanical properties of porous media

Geological sequestration of CO₂ in deep saline formations is a promising means of reducing atmospheric CO₂ emissions. Once injected, CO₂ dissolves into formation brine, lowering pH and creating conditions favorable for mineral dissolution. Cations released from dissolving minerals may create conditions favorable for secondary mineral precipitation which can result in the long-term mineralogical trapping of injected CO₂. These reactions may alter the natural rock mechanical properties, which can affect the safety and efficiency of geological sequestration. This work aims to investigate the impact of mineral composition and distribution on the mechanical properties of porous media. In this study, laboratory experiments are coupled with numerical simulations to evaluate the mechanical response of unreacted and acid-reacted Escambia county limestone samples. Here, samples were exposed to synthetic acidified formation brine for a period up to 12 weeks. Unreacted and reacted samples were then tested to determine their mechanical properties. The mechanical properties of the rock samples were analyzed using the unconfined compression and indirect tensile tests. The mineral composition and distribution are determined through analysis of scanning electron microscopy images of unreacted and reacted samples. A constitutive model was then developed based on the chemo-plasticity framework and compared with the experimental data. The experimental and numerical results showed that mechanical properties vary with composition, with important practical consequences for geological sequestration of CO₂.