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The main challenge of the application of nanofluids for enhanced oil recovery (EOR) in oil-wet carbonate reservoirs is maintaining their stability under high-temperature and high-salinity which is normally seen in reservoir conditions. In this work, surface-modified TiO2 nanoparticles were synthesized by N-(2-Aminoethyl)-3-Aminopropyltrimethoxysilane (AEAPTMS) as a coupling agent for surface modification of nanoparticles. Zeta potential and dynamic light scattering analyses were used to evaluate the stability of the prepared nanofluids. Results indicated that nanofluids had high stability in 90 °C and 20 wt.% salinity. The influence of nanofluids on wettability alteration of carbonate rocks was studied by measuring the contact angle value. Untreated rock samples were strongly oil-wet, with water advancing and receding contact angles of 165.1° and 166.2°, respectively. After treatment with 3wt.% concentration of surface-modified TiO2 nanoparticles, the rock plate wettability changed to a water-wet state, with water advancing and receding contact angles of 37.6° and 48.2°, respectively. Suggested surface-modified TiO2 nanoparticles were more effective in wettability alteration of the rock surfaces compared to the un-modified TiO2 nanoparticles. Furthermore, higher concentration of nanoparticles, higher the ability of the nanoparticles on changing the rock wettability.

The main challenge of the application of nanofluids for enhanced oil recovery (EOR) in carbonate reservoirs is to maintain colloidal stability under reservoir conditions with high salinity and high temperature. In this study, we address this issue by increasing the stability and hydrophilicity of ZnO nanoparticles by adding TTIP. Adding TTIP on the surface of ZnO nanoparticles results in an increase in the hydrophilic heads in the final product. Then, these nanoparticles are used to coat carbonate rock surfaces to change their wettability. The coated rock plates are obtained by aging them in nanofluids. The modified ZnO-based coatings show to be more effective for wettability alteration purposes compared to the conventional ZnO coating. The un-coated rock plate is strongly oil-wet, where the water and n-heptane droplets contact angles on this surface are 168° and 0°, respectively. After aging the rock samples in nanofluids, superhydrophilic coatings form on the superhydrophobic surfaces. The rock surface before and after treatment, as well as the synthesized nanoparticles, are characterized by scanning electron microscope (SEM), x-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) analyses. Results of this study indicate the possibility of using the materials for wettability alteration of oil-wet carbonate rock in the EOR process. The results of core flooding tests demonstrate that the oil recovery enhances significantly through the nanofluid flooding.

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