Nano-polymer–assisted enhanced oil recovery in oil wet carbonate formations: Coreflood experimental insights

Carbonate reservoirs in the Arabian Gulf present persistent challenges for chemical enhanced oil recovery (EOR) due to strongly oil-wet surfaces, high-salinity formation waters (∼168,000 ppm TDS), and pore-scale heterogeneity that collectively limit displacement efficiency during conventional waterflooding. Despite growing interest in hybrid chemical EOR, the comparative performance of spherical silica and single-walled carbon nanotube (SWCNT) nanoparticles combined with ATBS-modified HPAM polymers remains poorly characterized under high-salinity carbonate conditions. This study presents a systematic experimental investigation encompassing rheological characterization, static adsorption, contact angle analysis on aged carbonate surfaces, and sequential core flood experiments i.e., waterflooding, standalone nanoparticle flooding, and hybrid nano-polymer injection conducted at ambient temperature (∼25°C) on cores aged at 80°C to replicate oil-wet reservoir conditions, using injection brine of ∼44,000 ppm TDS. All hybrid formulations (Sav10 at 3000 ppm and Sav10 VHM at 2000 ppm, each with 750 ppm silica or SWCNT) sustained ∼4 cP viscosity at reservoir-relevant shear rates, confirming effective mobility control. Standalone nanoparticle flooding contributed 2.3–18.1% OOIP incremental recovery beyond waterflood, with the hybrid stage adding a further 3.3–17.6% OOIP; SWCNT-based hybrids reached total recoveries of 80.6–83.0% OOIP versus 63.6–71.1% for silica counterparts. SWCNT systems achieved lower final contact angles (39–40°) compared to silica (46–50°), and the SWCNT-Sav10 combination exhibited the lowest residual resistance factor (RRF = 1.01), indicating near-complete permeability restoration and the most favorable injectivity profile. These results establish a laboratory foundation for hybrid nano-polymer EOR in high-salinity oil-wet carbonate reservoirs; numerical simulation, temperature-dependent coreflood performance, interfacial tension measurement, and techno-economic assessment are recommended as priority directions for future work.