Nanoparticle was proposed as a new Enhanced Oil Recovery (EOR) agent for its great potential of increasing oil recovery and wettability alteration was suggested as one of main EOR mechanisms. We conducted a series of core flooding experiments with nanoparticles fluid (nanofluid) as tertiary recovery method. Core plugs injected by nanofluid were performed for Amott test to measure wettability index and showed the effect of nanofluid injection on wettability alteration. During core flooding experiment aged Berea sandstone cores were employed and pressure drop across core was measured, oil production rate was recorded as well. Hydrophilic silica nano-structure particles and hydrophilic silica colloidal nanoparticles with different concentration were utilized in above experiments. The objective of this experimental study is to investigate wettability change of core during nanofluid flooding process and its effect on oil recovery.

The results showed that injection of nanofluid can increase oil recovery, for some cases effect of nanofluid flooding on recovery is quite significate. Colloidal nanoparticles fluid injection didn't affect pressure drop obviously, while pressure drop increased significantly during nano-structure particles fluid flooding, which might be one of EOR mechanisms. Nanofluid flooding can change core to be more water wet and presence of crude oil can affect wettability alteration process by nanoparticles. However, increase of wettability index is independent of nanoparticles concentration.

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