Polymer-coated silica nanoparticles (PSiNP) have been proposed for enhanced oil recovery (EOR) owing to their improved properties such as stability, emulsion formation, low retention, etc. over bare nanoparticles. Even though most studies report EOR potential of nanoparticles compared to plain water flood, the underlying oil recovery mechanisms of nanoparticles are not well understood. This experimental work investigates the efficiency of PSiNP for oil recovery on micro-scale via comparing waterflooding to nanofluid flooding with minimizing the variations in pore architecture and initial oil connectivity on the trapping efficiency.

This research unleashes the potential application of four types of PSiNPs for EOR in water-wet Berea sandstone reservoirs and microfluidic chips. The PSiNPs were mixed with synthetic seawater at 0.1 wt % concentration. The oil recoveries were compared with waterflooding obtained on the same core. For this purpose, the following experiments were performed: First, four waterfloods were carried out until there was no oil production on four cores. Then, the cores were cleaned and dried. Afterwards, each core was injected with nanofluid in secondary recovery mode. To compare the four types of PSiNPs, microfluidic experiments were performed under the same experimental conditions such as pore-structure and initial oil connectivity. Measurements of interfacial tension and contact angle, and analysis of differential pressure across the cores and pore-scale images were performed to reveal possible recovery mechanisms of PSiNPs.

The nanofluids had higher ultimate oil recoveries than plain waterflood. The PSiNPs with small particle sizes had the highest reduction in IFT and the best capability to disconnect and minimize the size of the residual oil clusters within the pore spaces. Our hypothesis is that the adsorption of PSiNPs on the grain surfaces played a considerable role in the oil displacement efficiency. On the other hand, the ability of PSiNPs to cause pore-blockage and log-jamming attributed to the large NP size and adsorption on surfaces was strongly related to the displacement efficiency. Performing screening experiments of different nanofluids on cores with similar petrophysical properties could produce misleading results. Microfluidic experiments have advantages over the core-flooding experiments. Since the microchip has different properties compared to natural rocks; the results did not correlate with core-scale experiments. However, it was a significant tool, in this work, to indicate the generation of emulsions and the rate of clusterization, which cannot be seen from conventional core-scale experiments.

The knowledge gained from this experimental work helps to improve the screening methodology for the use of recovery agents such as nanoparticles for EOR applications.

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