Evolution of In Situ Wettability and Capillary Displacements in Carbonate Rocks: The Effect of Injection Brine Composition

Ion-specific interactions at fluid-mineral interfaces play a critical role in controlling wettability and multiphase flow in porous materials. In this study, a series of two-phase flow experiments were conducted on miniature oil-wet carbonate cores to investigate how aqueous chemistry regulates dynamic wettability evolution and pore-scale displacement behavior. Companion cores were conditioned using a common aging protocol to establish comparable mean oil-wet states and subsequently subjected to waterflooding under controlled chemical environments. Fluid configurations and in situ geometric contact angles were characterized at successive imaging stages using high-resolution X-ray microcomputed tomography. As wettability evolved in response to controlled aqueous chemistry toward less oil-wet states, the pathways of pore-scale invasion were correspondingly reorganized. Morphology-based analysis of the oil displaced between consecutive imaging stages quantified the relative volume contributions of piston-like invasion and wetting-layer drainage to incremental oil recovery. Piston-like invasion dominated initial displacement, whereas wetting-layer drainage accounted for most later-stage recovery during low-salinity flooding. These stage-dependent contributions connect brine-associated wettability changes with the pore-scale processes responsible for oil mobilization.