Carbonate precipitation characteristics in porous media of deep-sea cold seep environment by X-ray CT imaging

Elucidating the developmental processes of cold-seep carbonates is essential for understanding the evolutionary dynamics of methane cycling in cold-seep ecosystems. Cold-seep carbonates, as products of anaerobic methane oxidation, play an important role in regulating the oceanic carbon cycle. However, the mechanisms driving carbonate precipitation remain poorly understood. This study employs X-ray computed tomography to visualize bicarbonate ion concentration and sedimentary layer dynamics at pore scales (μm) in a deep-sea cold-seep environment. The results reveal that carbonate precipitation, driven by fluid supersaturation, is preferentially promoted at the sand column base by slower flow and solute accumulation, thereby generating spatial heterogeneity. Specifically, the optimal precipitation rate of 1.36 mm³/min occurs under conditions of the 420−600 μm medium-particle system and 0.06 mol/L bicarbonate concentration. The precipitation process follows a localized clogging mechanism, which in turn reduces hydraulic conductivity nonlinearly relative to porosity. Furthermore, differences in fluid mobility induce reconfigurations in fluid flow networks, ultimately prompting lateral migration and the formation of novel flow patterns. These findings provide crucial insights into carbonate formation mechanisms of, carbonate kinetics, and marine biological carbon sequestration processes.