Migration mechanisms of oil-water-sand three-phase flow in unconsolidated sandstones during water flooding: An image analysis approach resilient to threshold interference

Abstract

Unconsolidated sandstone reservoirs exhibit high sand production susceptibility during water flooding, impairing fluid migration and well productivity. Elucidating three-phase (oil-water-sand) migration mechanisms and residual fluid distribution characteristics is critical for sanding rate prediction and fluid saturation estimation. This study examines sand migration and residual oil distribution during waterflooding in unconsolidated sandstone oil reservoirs. Using methylene blue-dyed water to flood artificial models, we replicated sand production patterns and quantified outcomes via novel image analysis. Results show that: In water flooding processes through heterogeneous unconsolidated sandstones, sand production rate exhibits a quadratic polynomial relationship with time. Greater fluctuation ranges in areal sweep variation rates indicate frequent flooding front diversions. Post-flood residual oil saturation measures 66.07–71.87 % in heterogeneous models versus 70.99–76.65 % in homogeneous counterparts. Residual oil saturation demonstrates broader distribution in swept zones of heterogeneous formations, whereas homogeneous systems show localized concentration. Strategic injection placement in high-permeability zones induces enhanced sweep efficiency when fluid propagates into low-permeability regions, establishing optimized drainage networks. These insights aid sand control and residual fluid management during fluid injection/production. The image analysis method enables pore-scale quantitative characterization for aquifer management and contaminant remediation.