Wettability, pore occupancy, connectivity and Ostwald ripening of nitrogen, carbon dioxide, and hydrogen in carbonate rocks: A comparative study

High-resolution three-dimensional X-ray imaging was employed to evaluate the injection of nitrogen (N 2 ), carbon dioxide (CO 2 ), and hydrogen (H 2 ) in a reservoir carbonate rock. The imaging data were analyzed to determine key properties, including wettability, gas saturation, pore occupancy, ganglia size, and connectivity throughout the sample. The experiment was conducted on a water-wet carbonate rock saturated with synthetic brine prior to and between each gas injection cycle. The work demonstrates key differences in the behavior of the gases: H 2 undergoes more significant rearrangement and improved connectivity after injection compared to N 2 , while CO 2 remains well connected but exhibits the least rearrangement. This is advantageous of hydrogen withdrawal, whereas improved connectivity is not favorable for long-term CO 2 sequestration. These findings are critical when considering the design and optimization of subsurface storage projects, where enhanced gas mobility benefits H 2 recovery but poses risks for CO 2 leakage. • High-resolution 3D X-ray imaging reveals gas behavior in water-wet carbonate rocks. • H 2 shows enhanced pore connectivity and rearrangement, beneficial for gas withdrawal. • CO 2 shows stable saturation (good) but high connectivity (bad) for long-term sequestration. • Capillary pressure declines most for N 2 , moderate for CO 2 , and remains stable for H 2 . • All gases display low contact angles (<20°), confirming water-wet conditions.