Microscopic Waterflooding and Residual Oil Distribution Characteristics in Ultra-Low Permeability Sandstone

HIGHLIGHTS (1) Fingering phenomenon is prevalent in ultra-low permeability rocks, with throat radius and pore structure heterogeneity significantly influencing displacement paths and the degree of fingering. (2) Mixed-wettability notably aggravates fingering, and the wettability at the pore inlet is the dominant factor controlling flow paths and displacement efficiency. (3) Injection rate and wettability affect oil-water flow in pores by controlling the dynamic competition between viscous and capillary forces.