Towards Understanding Pore-Scale Carbonate Reactivity for Geologic Carbon Sequestration

Abstract

Geological carbon sequestration (GCS) is a promising method to reduce atmospheric carbon dioxide emissions by capturing CO2 and securely storing it long-term in deep subsurface rock formations. The goal is to sequester CO2 so it cannot re-enter the Earth’s atmosphere. Assessing a geological formation's capacity for secure storage requires in depth characterization of formation properties such as mineral abundance, porosity, and pore accessibility. This work evaluates a dolomite-rich carbonate sample sourced from Cassville, GA that is being considered as a potential CO2 storage reservoir to help determine its suitability. This work additionally contributes to a broader understanding of carbonate reservoirs as candidates for carbon sequestration in the southeastern United States. Here, Scanning Electron Microscopy (SEM) images are collected for the sample and processed to create detailed mineral maps. These maps are quantitatively analyzed to determine the sample's porosity and mineral composition. Integrating the SEM imaging and two-dimensional data provides a robust characterization of the reservoir's microstructure and its implications for caprock integrity and geochemical reactivity. Ultimately, this supports site selection, modeling, and risk assessment for geological carbon storage projects. While high resolution imaging provides baseline reservoir sample characteristics, predicting long-term storage viability requires evaluating fluid-rock interactions like mineral dissolution and precipitation through laboratory experiments. However, accurately assessing these interactions and impacts on pore structure require a method to dry experimental columns and removing fluids without causing further reactions. When running these experiments, it is crucial to halt chemical reactions rapidly and effectively. Furthermore, the drying process must retain the natural three-dimensional pore structure of the sample so that post-experiment imaging and analysis accurately reflect the true results of the reaction rather than what was left over after drying. To determine the most effective approach for sample drying and preservation, the study compares two distinct drying methods: an ethanol flush and an isopropanol flush. By evaluating how well each method displaces water while protecting the structural and mineralogical integrity of the rock, the goal is to establish a reliable technique that prevents artificial precipitation and ensures laboratory results remain accurate.