| dc.description.abstract | 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. A microfluidic approach was utilized to perform flooding experiments with constant experimental settings such as flowrate, pore-structure, initial oil topology, porosity, and permeability. 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. In addition, this work also investigates the efficiency of PSiNPs for oil recovery on micro-scale at three wettability states (water-wet, intermediate-wet, and oil-wet). In addition, a cluster mobilization regime is considered in all experiments.
First application 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.
Second and third applications are low-rate and step-rate experiments in brine-oil- and nanofluid-oil-glass systems of each wettability condition, and they showed that the waterflood invaded with a more stable front with a slower displacement velocity in the water-wet state compared to the other states, which had water channelling through the big pores. As a result, a faster stop of the dynamic changes for the intermediate- and oil-wet state was observed, leading to lower oil recoveries compared to the water-wet state. In a cluster mobilization regime, dynamic changes were noticeable only for the oil-wet condition. For the aforementioned different conditions, PSiNPs improved oil displacement efficiency. The usage of PSiNPs showed a better clusterization efficiency, leading to a higher mobilization, smaller remaining oil clusters, and lower connectivity of the residual oil.
The knowledge gained from these experimental works help to improve the screening methodology for the use of recovery agents such as nanoparticles for EOR applications. Furthermore, these experimental works add to the understanding of the behaviour of polymer-coated silica nanoparticles as a recovery agent at different wettability states and a cluster mobilization regime. | |