Pore Structure Alterations in Calcite and Dolomite Resulting from the Interaction with CO2 - Insights into Geological Storage.

Geological carbon storage is a key strategy for reducing CO₂ emissions by capturing CO₂ from large point sources and injecting it into deep saline aquifers or depleted oil and gas reservoirs. The effectiveness of this process depends critically on the petrophysical properties of the storage formation. In carbonate rocks, CO₂-fluid interactions can lead to dissolution or precipitation, significantly altering porosity and permeability. This study investigates the impact of CO₂-carbonate interactions using high-resolution microCT imaging. Outcrop samples of Indiana Limestone and Silurian Dolomite were exposed to carbonated water (CW) and supercritical CO₂ (SCO₂) for 14 and 28 days under controlled conditions. MicroCT scans revealed marked differences in pore structure evolution. Indiana Limestone, composed primarily of calcite, showed significant pore enlargement and enhanced connectivity, especially within the first 14 days, with greater reactivity under CW conditions. Silurian Dolomite exhibited more heterogeneous and spatially constrained reactivity. Quantitative imaging analyses confirmed that dissolution was more pronounced in liquid phase, suggesting carbonic acid as a key agent in matrix degradation. The results highlight a non-linear porosity evolution trend, indicating early-stage dissolution followed by a stabilization. These findings emphasize the role of mineralogy, fluid phase, and exposure duration in governing CO₂-induced alterations in carbonate rocks.