Performance Assessment and Optimization of Hybrid Nano-Polymer Flooding in Carbonate Reservoirs

Abstract Innovative chemical enhanced oil recovery (CEOR) strategies are essential to unlock residual reserves in oil-wet carbonate formations, where conventional waterflooding offers limited displacement efficiency. This study investigates a novel hybrid nano-polymer flooding approach by integrating silica nanoparticles (SiO₂) and single-walled carbon nanotubes (SWCNTs) with a very-high-molecular-weight partially hydrolysed polyacrylamide-based polymer (Sav10VHM), aiming to optimize mobility control and wettability alteration thus resulting in incremental oil recovery. A comprehensive experimental program was executed, involving polymer rheology, nanoparticle induced wettability alteration and dynamic coreflood studies for oil wet carbonate reservoirs. Rheological evaluations confirmed that Sav10VHM, at an optimized concentration of 2,000 ppm, maintained viscosities well above the target viscosity of 4 cP and exhibited favourable shear thinning behaviour. Nanoparticle wettability tests demonstrated strong wettability shifts, with silica reducing contact angles from 164° to 38.5° and SWCNTs from 163° to 37.6°. Hybrid systems preserved both viscosity and surface-alteration capability, with Sav10VHM-SWCNT exhibiting the strongest wettability response, reducing contact angles from 169° to 38.8°. Corefloods were performed in three stages: baseline waterflood, standalone nanoparticle injection, and hybrid nano-polymer flooding. The Sav10VHM-Silica system achieved a final recovery of 71.12%, while the Sav10VHM–SWCNT system reached 82.98%, driven by synergistic rheological performance and enhanced rock–fluid interaction. Differential pressure trends indicated improved sweep and flow diversion with the hybrid systems, particularly in SWCNT based floods. The superior performance of SWCNT hybrids highlights their underexplored potential in carbonate EOR. This study presents core scale assessments of SWCNT-HPAM hybrid flooding, offering compelling evidence for their application in carbonate reservoirs and suggesting future work in interfacial tension (IFT) analysis, injectivity behaviour, and field-scale pilot testing.