Abstract
Wettability alteration was proposed as one of the enhanced oil recovery (EOR) mechanisms for nanoparticle fluid (nanofluid) flooding. The effect of nanoparticle adsorption on wettability alteration was investigated by wettability index measurement of Berea sandstone core injected with nanofluids and by contact angle measurement of a glass surface treated with nanofluids. Nanoparticle adsorption was studied by single phase coreflooding with nanofluids in Berea sandstone. The adsorption isotherm and the impact of adsorption on the effective permeability were investigated by measuring the effluent nanoparticle concentration and differential pressure across the core. Results showed that hydrophilic nanoparticles (e.g. fumed silica) made the core slightly more water wet, and hydrophobic nanoparticles (e.g. silane modified fumed silica) delayed spontaneous imbibition but could not alter the original wettability. It was found that hydrophilic nanoparticles treatment reduced contact angle between oil and water by about 10 to 20 degree for a glass surface. Results also showed that different types of nanoparticle have different adsorption and desorption behavior and different ability to impair the permeability of Berea sandstones cores.
Highlights
The wettability of reservoir rock plays an important role in oil field development
Since all core plugs were drilled from the same block of Berea sandstone, we assumed that the original wettability index for all cores plugs before nanoparticles treatment was 0.795
For core plugs treated with 0.5 wt.% nanofluids, they should have the similar wettability index value with 0.05 and 0.2 wt.% cases, while the results showed that they were slightly less water wet than the original cores
Summary
The wettability of reservoir rock plays an important role in oil field development. It controls the relative permeability, capillary pressure, and residual oil distribution. Surfactant flooding was utilized to alter reservoir rock wettability to more water wet, which can enhance spontaneous imbibition and increase oil recovery during water injection [2, 3]. Hammond and Unsal [4] discussed the possible mechanisms of wettability alteration with surfactants. They include surfactant adsorption onto rock surface and surfactant complexing with contaminant molecules of crude oil that are adsorbed on the rock surface and stripping them off. Salehi et al studied the mechanisms of wettability alteration using surfactant in naturally fractured reservoirs, they found that both ion-pair formation and Wettability Alteration by Nanoparticle Adsorption adsorption of surfactant molecules are the two main mechanisms responsible for altering the rock wettability to more water-wet, and surfactants with higher charge density on the head groups were more effective in altering wettability to a more waterwet state [2]
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