Research on microscopic displacement mechanism of slickwater in different pore sizes

To address the challenges like low recovery efficiency and rapid production decline following conventional hydraulic fracturing in tight reservoirs, fracturing oil-displacement integration has garnered significant attention. However, the microscopic effects of slickwater invasion during these operations remain insufficiently understood. Previous studies have typically focused on either its oil displacement ability or its effect on pore structure, rarely investigating the direct link between them. This study compares the microscopic displacement mechanisms of slickwater and formation water using interfacial tension measurements, contact angle measurements, core flooding experiments, nuclear magnetic resonance (NMR) analysis, and scanning electron microscopy analysis on identical artificial sandstone cores. While slickwater exhibits better interfacial properties, the results show that its primary enhanced oil recovery mechanism is a three-stage oil displacement pattern by pore volume (PV), which increases ultimate recovery by approximately 5%. NMR T2 spectra reveal that in the early stage (<2 PV), slickwater's higher viscous forces rapidly activate macropores. In the middle stage (2–5 PV), polymer-induced blockage of primary channels forces a flow diversion into previously bypassed mesopores. Finally, in the late stage (>5 PV), there is limited additional recovery. However, the polymer retention causes severe core damage, leading to a 70.2% reduction in permeability. NMR analysis proves slickwater preferentially invades mesopores and macropores, and post-flooding SEM images directly visualize polymer aggregates plugging these pathways, confirming the pore structure variations. This work quantifies the dual role of slickwater in enhancing recovery through flow diversion while altering pore structure, providing critical insights for optimizing fracturing oil-displacement integration.