Engineering Hybrid Nano-Polymer Interfaces for Multi-Scale Low-Salinity Recovery in Carbonate Reservoirs

Abstract

Enhanced oil recovery (EOR) in oil-wet carbonate reservoirs remains challenging due to unfavourable wettability, strong oil-rock interactions, and limited sweep efficiency. This study evaluates hybrid nano–polymer flooding using SAV10 polymer combined with silica (SiO₂) nanoparticles and single-walled carbon nanotubes (SWCNTs) to assess their impact on rheology, wettability alteration, and oil recovery in carbonate cores under low-salinity conditions. A structured experimental workflow was implemented, including salinity screening, nanoparticle concentration optimization, polymer rheology evaluation, and dynamic coreflood testing. Rheological analysis identified 1000 ppm SAV10 as the optimal polymer concentration, providing a stable viscosity of approximately 3 cP with favourable shear-thinning behaviour. Wettability measurements showed that silica reduced contact angle from 130.72° to 28.52°, while SWCNT reduced it from 134.81° to 44.1°. Hybrid formulations preserved these wettability shifts, confirming nanoparticle–polymer compatibility. Coreflood experiments demonstrated 7% incremental recovery from standalone silica and 7% from silica-polymer flooding, whereas SWCNT achieved 11% incremental recovery and the hybrid SWCNT-polymer system delivered 12%. Pressure response during flooding remained stable for all cases, indicating favorable injectivity and minimal formation impairment. These results highlight the effectiveness of low-salinity hybrid nano–polymer flooding and the comparatively stronger displacement performance of SWCNT based systems in oil-wet carbonates.