Understanding Mineral Dissolution in Porous Media Coupled With Single- and Multi-phase Flows: A Coordinated Experimental and Numerical Study

The increasing buildup of carbon dioxide (CO2) in the atmosphere contributes to a wide range of environmental, social, and economic problems. One viable way to mitigate CO2 emission is through an operation called carbon capture and sequestration (CCS). In CCS, CO2 is captured from power plants, and injected into underground saline aquifers. However, injection of CO2 into geologic formations leads to dissolution of minerals due to the acidic nature of CO2, which can create leakage pathways and threaten the safety and security of CO2 storage. Therefore, an accurate knowledge of mineral dissolution in saline aquifers is needed to design effective, safe, and efficient CCS operations. The goal of this project is to bridge this knowledge gap through coordinated lab experiments and numerical simulations. Innovative fabrication, flow visualization, and simulation techniques will be combined to understand the chemical and physical processes that drive rock dissolution. More broadly, successful completion of this research can also benefit studies on agriculture, soil formation, and underground cave geology, as similar processes occur in these systems. Further benefits to society will result from diversifying the STEM workforce through training and education of female and Native American students, creating YouTube contents as educational materials for the public, and supporting two major campus-wide outreach events including the Earth and Science Explore Camp and Montana State Family Science Night. Reactive dissolution of minerals in porous media is pervasive in natural and engineered systems. The greatest challenge to understanding these porous media systems is that dissolution rates measured in the lab are typically orders of magnitude higher than those observed in the field, referred to as the “lab–field discrepancy”. This mismatch not only poses strong challenges in developing accurate predictive models, but also highlights a lack of fundamental knowledge of mineral dissolution. It has been hypothesized the lab-field discrepancy is primarily due to concentration gradients resulting from incomplete mixing within individual pores that are in turn subject to heterogeneous flow fields at the microscopic scale. Unfortunately, little data or understanding is available on the pore-scale processes that occur during mineral dissolution because of the difficulty in directly measuring flow dynamics and transport at the pore level. The goal of the proposed research is to achieve a transformative understanding of pore-scale transport and chemical reaction in porous media to reconcile the long-standing “lab-field discrepancy.” Successful resolution of this problem will pave the way for more accurate macroscopic predictions. This will be achieved through a coordinated experimental and simulation framework employing microfluidic micromodels and the lattice Boltzmann method. The micromodels will be fabricated in naturally occurring calcite, which enables the precise construction of porous media closely representing real geological systems. Dissolution will be induced by injection of hydrochloric acid at various concentrations and flow rates to simulate realistic CCS operations. Interactions between pore-scale flow and mineral dissolution will be directly quantified, providing valuable insight into the underlying physics to facilitate proper upscaling. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.