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Any efficient exploitation of new petroleum reservoirs necessitates developing methods to mobilize the crude oils from such reservoirs. Here silicon dioxide nanoparticles (SiO 2 NPs) were used to improve the efficiency of the chemical-enhanced oil recovery process that uses surfactant flooding. Specifically, SiO 2 NPs (i.e., 0, 0.001, 0.005, 0.01, 0.05, and 0.1 wt%) and Tween Ò 20, a nonionic surfactant, at 0, 0.5, and 2 critical micelle concentration (CMC) were varied to determine their effect on the stability of nanofluids and the interfacial tension (IFT) at the oil-aqueous interface for 5 wt% brine-surfactantSiO 2 nanofluid-oil systems for West Texas Intermediate light crude oil, Prudhoe Bay medium crude oil, and Lloydminster heavy crude oil. Our study demonstrates that SiO 2 NPs may either decrease, increase the IFT of the brinesurfactant-oil systems, or exhibit no effects at all. For the brine-surfactant-oil systems, the constituents of the oil and aqueous substances affected the IFT behavior, with the nanoparticles causing a contrast in IFT trends according to the type of crude oil. For the light oil system (0.5 and 2 CMC Tween threshold concentration resulted in a decrease in IFT, and concentrations above this threshold resulted in an increase in IFT. The IFT decreased until the NP concentration reached a threshold concentration where synergetic effects between nonionic surfactants and SiO 2 NPs are the opposite and result in antagonistic effects. Adsorption of both SiO 2 NPs and surfactants at an interface caused a synergistic effect and an increased reduction in IFT. The effectiveness of the brine-surfactant-SiO 2 nanofluids in decreasing the IFT between the oil-aqueous phase for the three tested crude oils were ranked as follows: (1) Prudhoe Bay [ (2) Lloydminster [ and (3) West Texas Intermediate. The level of asphaltenes and resins in these crude oil samples reflected these rankings. A decrease in the IFT also indicated the potential of the SiO 2 NPs to decrease capillary pressure and induce the movement and recovery of oil in original water-wet reservoirs. Conversely, an increase in IFT indicated the potential of SiO 2 NPs to increase capillary pressure and oil recovery in reservoirs subject to wettability reversal under water-wet conditions. Raspberrylike morphology particles were discovered in 5 wt% brinesurfactant-SiO 2 nanofluid-oil systems. The development of raspberry-like particles material with high surface area, high salt stability, and high capability of interfaces alteration and therefore wettability changes offers a wide range of applications in the fields of applied nanoscience, environmental engineering, and petroleum engineering.

Abstract. The vadose zone is a highly interactive heterogeneous system through which water enters the subsurface system by infiltration. This paper details the effects of simulated plant exudate and soil component solutions upon unstable flow patterns in a porous medium (ASTM silica sand; US Silica, Ottawa, IL, USA) through the use of two-dimensional tank light transmission method (LTM). The contact angle (θ ) and surface tension (γ ) of two simulated plant exudate solutions (i.e., oxalate and citrate) and two soil component solutions (i.e., tannic acid and Suwannee River natural organic matter, SRNOM) were analyzed to determine the liquidgas and liquid-solid interface characteristics of each. To determine if the unstable flow formations were dependent on the type and concentration of the simulated plant exudates and soil components, the analysis of the effects of the simulated plant exudate and soil component solutions were compared to a control solution (Hoagland nutrient solution with 0.01 M NaCl). Fingering flow patterns, vertical and horizontal water saturation profiles, water saturation at the fingertips, finger dimensions and velocity, and number of fingers were obtained using the light transmission method. Significant differences in the interface properties indicated a decrease between the control and the plant exudate and soil component solutions tested; specifically, the control (θ = 64.5 • and γ = 75.75 mN m −1 ) samples exhibited a higher contact angle and surface tension than the low concentration of citrate (θ = 52.6 • and γ = 70.8 mN m −1 ). Wetting front instability and fingering flow phenomena were reported in all infiltration experiments. The results showed that the plant exudates and soil components influenced the soil infiltration as differences in finger geometries, velocities, and water saturation profiles were detected when compared to the control. Among the tested solutions and concentrations of soil components, the largest finger width (10.19 cm) was generated by the lowest tannic acid solution concentration (0.1 mg L −1 ), and the lowest finger width (6.00 cm) was induced by the highest SRNOM concentration (10 mg L −1 ). Similarly, for the plant exudate solutions, the largest finger width (8.36 cm) was generated by the lowest oxalate solution concentration (0.1 mg L −1 ), and the lowest finger width (6.63 cm) was induced by the lowest citrate concentration (0.1 mg L −1 ). The control solution produced fingers with average width of 8.30 cm. Additionally, the wettability of the medium for the citrate, oxalate, and SRNOM solutions increased with an increase in concentration. Our research demonstrates that the plant exudates and soil components which are biochemical compounds produced and released in soil are capable of influencing the process of infiltration in soils. The results of this research also indicate that soil wettability, expressed as (cos θ )

Abstract. The vadose zone is a highly interactive heterogeneous system through which water enters into the subsurface system by infiltration. This paper details the effects of simulated plant 15 exudate and soil component solutions upon unstable flow patterns in a porous media (ASTM silica sand; US Silica, Ottawa, IL, USA) through the use of two-dimensional (2D) tank light transmission method (LTM). The contact angle and surface tension of two simulated plant exudate solutions (i.e. oxalate, and citrate) and two soil component solutions (i.e. tannic acid, and Suwannee River Natural Organic Matter) were analyzed to determine the liquid-gas and liquid-20 solid interface characteristics of each. To determine if the unstable flow formations were dependent on the type and concentration of the simulated plant exudates and soil components, the analysis of the effects of the simulated plant exudate and soil component solutions were compared to a control rainwater solution. The differences in the fingering flow were quantified with the finger geometries, the velocity of finger propagation, the vertical and horizontal water 25 saturation profiles, and the water saturation at the fingertips. Significant differences in the interface processes indicated a decrease between the control and the plant exudate and soil component solutions tested; specifically, the control at 64. 2 solutions further demonstrate that the plant exudates increased the wettability and mobility of the solutions during the infiltration process in unsaturated porous media.