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 (similar to 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 (similar to 25 degrees C) on cores aged at 80 degrees C to replicate oil-wet reservoir conditions, using injection brine of similar to 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 similar to 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 degrees) compared to silica (46-50 degrees), 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.