Nanoscale investigation of silicon dioxide nanofluids and implications for enhanced oil recovery – An atomic force microscope study

Abstract

The use of silica-based nanofluids in enhanced oil recovery (EOR) has received significant attention recently. Aqueous dispersion of silica nanoparticles (<100 nm) can improve oil recovery through wettability alteration via rock/fluid and fluid/fluid interactions. Silicon dioxide nanofluids also offer superior advantages such as controllable chemistry and environmental safety. The potential of these chemicals has been studied reasonably at larger scales through contact angle and force imbibition tests. However, there is inadequate scientific understanding of nanofluid EOR. Evidence of oil recovery at nanoscale is also limited, which is important for low-porosity and permeability petroleum rocks with nanopores. In this study, we conducted an atomic force microscopy (AFM) study to investigate the effect of silica-based nanofluids on wettability alteration in model sandstones at nanoscale. We used CH2- and C6H5- terminated functionalized AFM probes to represent saturated and aromatic crude oils (respectively), and quartz & feldspar minerals to represent model rock surfaces. Our results show that adhesion force between these non-polar moieties and minerals decrease with increasing nanofluid concentration. We demonstrate experimentally at nanoscale that silica nanofluids significantly reduces work of adhesion – a fundamental wettability indicator - between functionalized probes and substrates. Across all tests, we observed a threshold concentration of 0.5 wt% above which wettability is not improved. Our findings offer fresh insight into the fundamental investigations of oil release mechanism with dispersed nanoparticles and provide original evidence on the implications of nanofluid injection for enhanced oil recovery at sub-micron scale.