Surface modification of nanoparticles for enhanced applicability of nanofluids in harsh reservoir conditions: A comprehensive review for improved oil recovery.

Nanoparticles improve traditional Enhanced Oil Recovery (EOR) methods but face instability issues. Surface modification resolves these, making it vital to understand its impact on EOR effectiveness. This paper examines how surface-modified nanoparticles can increase oil recovery rates. We discuss post-synthesis modifications like chemical functionalization, surfactant and polymer coatings, surface etching, and oxidation, and during-synthesis modifications like core-shell formation, in-situ ligand exchange, and surface passivation. Oil displacement studies show surface-engineered nanoparticles outperform conventional EOR methods. Coatings or functionalizations alter nanoparticle size by 1-5 nm, ensuring colloidal stability for 7 to 30 days at 25 to 65 °C and 30,000 to 150,000 ppm NaCl. This stability ensures uniform distribution and enhanced penetration through low-permeability (1-10 md) rocks, improving oil recovery by 5 to 50 %. Enhanced recovery is achieved through 1-25 μm oil-in-water emulsions, increased viscosity by ≥30 %, wettability changes from 170° to <10°, and interfacial tension reductions of up to 95 %. Surface oxidation is suitable for carbon-based nanoparticles in high-permeability (≥500 md) reservoirs, leading to 80 % oil recovery in micromodel studies. Surface etching is efficient for all nanoparticle types, and combining it with chemical functionalization enhances resistance to harsh conditions (≥40,000 ppm salinity and ≥ 50 °C). Modifying nanoparticle surfaces with a silane coupling agent before using polymers and surfactants improves EOR parameters and reduces polymer thermal degradation (e.g., only 10 % viscosity decrease after 90 days). Economically, 500 ppm of nanoparticles requires 56.25 kg in a 112,500 m reservoir, averaging $200/kg, and 2000 ppm of surface modifiers require 4 kg at $3.39/kg. This results in 188,694.30 barrels, or $16,039,015.50 at $85 per barrel for a 20 % increase in oil recovery. The economic benefits justify the initial costs, highlighting the importance of cost-effective nanoparticles for EOR applications.