Experimental evaluation of nanoparticles impact on displacement dynamics for water-wet and oil-wet porous media
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The potential of utilizing nanoparticles for production enhancement during oil-water displacement can play a significant role to achieve efficient and sustainable production of resources as they have shown great promise in stabilizing emulsion inside porous media. Furthermore, the displacement of brine solution containing nanoparticles by another non-wetting phase such as n-octane under water-wet condition has been shown to produce the signs of nanoparticle-stabilized emulsion. Because it is hypothesized that emulsion effects are caused by pore scale events that shear the fluids, this research aims to evaluate the impact of nanoparticles on different displacement scenarios (primary imbibition, primary drainage, secondary imbibition, and secondary drainage) and address the effect of wettability (oil-wet vs. water-wet), displacement types (different pore scale processes), and viscous stability (lower viscosity n-octane vs. higher viscosity tetradecane) on the generation of nanoparticle-stabilized emulsion in situ during immiscible displacement. Studying the impact of these changes is of primary importance since they contribute to changing pore scale events, fluids positioning and distribution, and displacement stability. Nanoparticle-stabilized emulsion has been associated with some indirect observable signs which include i) a rapid pressure drop increase exceeding the viscosity ratio between the brine and brine-nanoparticle dispersion, ii) a later breakthrough, , iii) a reduction in resident fluid residual saturation, and iv) a reduction of the invading phase endpoint relative permeability. Therefore, the impact of nanoparticles on the displacement was evaluated by measuring pressure drop data and effluent fluid histories. Those data were used to indicate the signs of nanoparticle-stabilized emulsion generation by interpreting pressure drop trends, water saturation histories, pressure drop ratio profile, residual fluid saturation, and endpoint relative permeability of the invading phase. Furthermore, the study attempts to examine the hypothesis that the displacement of a wetting hydrocarbon phase containing hydrophobic nanoparticles by another non-wetting aqueous phase will also generate nanoparticle-stabilized emulsion symptoms. This research reveals that compared to the control case (no nanoparticles), nanoparticles have the greatest effect on drainage type displacement (hydrocarbon invasion) with pressure drop reaching up to 500 % or even greater compared to the initial pressure drop observed at the start of the displacement. It also shows that those particles have little effect on imbibition displacement (aqueous phase invasion). This was found to be true for both oil-wet and water-wet despite the fact that fluids are configured differently at the pore-scale level. As for a more viscous hydrocarbon phase (tetradecane), the observed effects are generally lessened. As for secondary drainage displacement, initial trapping and the distribution of the hydrocarbon phase has also reduced the severity of the emulsion generation process. Based on the previous findings, an attempt to test the hypothesis of displacing hydrophobic nanoparticle dispersion by an aqueous brine solution under oil-wet condition was inconclusive due to the difficulty of maintaining stable hydrocarbon-nanoparticle dispersion. The displacement profile for all imbibition cases showed no significant differences between nanoparticle case and control case. Yet, we observe that nanoparticles have caused a reduction in the residual hydrocarbon saturation. This reduction was slightly greater for water-wet core compared to oil-wet. For these results I conclude that Haines jump and Roof snap-off may be one of the primary processes responsible to generate nanoparticle-stabilized emulsion during drainage displacement. However, observing emulsion symptoms during secondary drainage in oil-wet cores suggest either a) exact configuration is not important or b) possible alteration in the rock wettability by nanoparticles to produce the same configuration. The viscosity results suggest that nanoparticle effects have largely altered the conformance of the displacement. The presence of ethylene glycol and/or other coating chemicals used to maintain stability of nanoparticle dispersion may have caused the reduction of hydrocarbon phase residual saturation during all imbibition type displacement.