Pore-scale reactive transport for assessing permeability changes on CO2 capture and storage

Reactive transport modeling has increasingly become a key simulation capability in the risk management of subsurface operations, particularly when dealing with reactive fluids, such as monitoring of CO₂ plume migration in carbon capture and storage (CCS) operations. The pore-scale complexities and mineral distribution play a fundamental role in the dynamic porosity and permeability exhibited by a rock upon invasion of a reactive fluid. Here, we present an implementation of pore-scale reactive transport (PSRT) – using a generalized rate law that can be extended to any mineral – for simulating the evolving pore geometry of a digital rock due to dissolution and precipitation reactions within the rock. We validate our implementation against a well-known single-mineral benchmark simulation case and previously published microfluidics experiments, before applying the framework to a realistic CCS scenario with multiple minerals using a $\mu \mathrm{CT}$ image from an appraisal well in Texas. For our sandstone comprising calcite, quartz, clay, and feldspar, we show total dissolution of calcite and delayed, nominal dissolution of anorthite over a 2-hour time frame, resulting in a 41.1% relative increase in porosity and a 242% relative increase in permeability in the absence of grain compaction effects. We demonstrate the importance of 3D PSRT simulations for CCS scenarios by investigating the heterogeneity of mineral reaction rates. Our approach reveals relationships between porosity–permeability and porosity–tortuosity that would not be captured by lower-dimensional methods. We show that these relationships can be directly observed from PSRT simulations and interpreted via a streamline analysis of the evolving flow fields.