Synergistic Effect on Enhanced Oil Recovery in High Salinity Carbonate Reservoirs Using a Novel PEI‐Functionalized Carbon Nanotube Nanocomposite

ABSTRACT Enhancing oil recovery (EOR) in mature reservoirs is hindered by high interfacial tension (IFT) and oil‐wet rock formations, especially under harsh, high‐salinity conditions. This study aims to overcome these limitations by synthesizing a novel carbon nanotube nanocomposite covalently grafted with polyethylenimine and non‐covalently functionalized with benzalkonium chloride (PEI/BAC/CNTs) to synergistically reduce IFT and alter rock wettability. The nanocomposite was synthesized via sequential oxidation, amidation, and surfactant assembly, and was structurally validated using XRD, FTIR, and EDS. Colloidal stability was evaluated via dynamic light scattering and zeta potential measurements. EOR performance was systematically assessed through IFT measurements, dynamic contact angle analyses on oil‐aged rocks, and dynamic core flooding using both high‐ and low‐acidic crude oils. The PEI/BAC/CNTs exhibited exceptional long‐term stability at an optimal concentration of 1000 ppm. At this dosage, the nanofluid dramatically reduced IFT to 4.1 mN/m for highly acidic crude oil and shifted the wettability of strongly oil‐wet rocks (from an initial contact angle of 146°) to a strongly water‐wet state (42°). Electrokinetic and spectroscopic analyses confirmed robust electrostatic interactions and hydrogen bonding at the fluid–solid interfaces. Furthermore, sequential dynamic core flooding demonstrated that the nanofluid recovered up to 71.4% of the original oil in place, significantly outperforming conventional waterflooding by promoting targeted flow diversion and mobilizing trapped oil ganglia. In conclusion, the synthesized PEI/BAC/CNTs nanocomposite provides a highly efficient, dual‐mechanism EOR approach, proving its potential as a technically robust and economically feasible chemical agent for advanced oil recovery in complex subterranean formations.