![Fig. 10 AFM height images [2D (1) and 3D (2)] of calcite crystals: A) Untreated calcite; B) Silane treated calcite; C) ZrO2 modified; D) NiO modified. The different colours indicate variation in height of the surface with high Z-values (higher features appearing as white) and low Z-values (lower features appearing as dark shades).](/figures/fig-10-afm-height-images-2d-1-and-3d-2-of-calcite-crystals-a-16mwi536.webp)
Q2. What is the effect of ZrO2 on wettability?
As the dispensed water droplets get in contact with the ZrO2 nanocoated calcite, the contact angle decreases more readily, thus wettability is efficiently changed towards water-wet at minimal particle concentration.
Q3. What was used as dispersing agent for all tests?
Ultrapure de-ionised water (from David Gray, conductivity 0.02mS/cm) and NaCl (purity ≥99.5 mol%, from Rowe Scientific) brine was used as dispersing agents for all tests.
Q4. What is the effect of particle size on the formation of limestone?
Nanoparticles with particle sizes <100nm inhibits direct plugging and bridging in the micropore network systems especially in the subsurface (Li and Cathles, 2014) as such can facilitate transport through the formation.
Q5. What is the wettability modifier for calcite?
Nanoparticles adsorbed on the surface of the calcite crystals promote oil displacementthus contributing to inevitable change in wettability from oil-wet to water-wet in a very efficient way.
Q6. What is the effect of adsorption on the surface of a silica nano?
ZrO2 has been employed in adsorption and conductivity studies in the presence of surfactants, where ZrO2 nanoparticle and surfactant formulations enhanced surface activity and adsorption behaviour (Esmaeilzadeh et al., 2011).
Q7. What are the promising alternatives to carbonate formations?
Nanoparticles (nanofluids) - though still in its early stages - are promising alternatives, especially metal oxide nanoparticles.
Q8. What is the effect of NaCl concentration on the calcite surface?
The particle adsorbed on the calcite surface with increase in NaCl concentration which can be attributed to the physiochemical interactions or electrostatic forces (Li and Cathles 2014; Zhang et al., 2013) between the nanofluid and calcite.
Q9. What was used to clean the calcite substrates?
The calcite substrates were initially cleaned with analytical reagent grade acetone andmethanol (Rowe Scientific pty. Ltd) and de-ionised water (David Gray & Co. Ltd) to remove surface impurities.
Q10. What is the main mechanism for hydrocarbon recovery?
The main mechanism for hydrocarbon recovery, spontaneous imbibition of water into the matrix blocks, is often disrupted due to the oil-wet or intermediate-wet character of the limestone (Chabert et al., 2010; Rezaei Gomari and Hamouda, 2006; Thomas et al., 1993) and associated low (water) suction pressures (Strand et al., 2006).
Q11. What is the effect of a large surface area on the particle?
This large surface area enhances surface energy of the particles which causes structural transitions (Tsuzuki, 2013) and permits favourable particle adsorption at the surface boundaries and can also exhibit high tendencies of being in contact with other neighbouring materials.
Q12. What is the effect of the addition of a small fixed fraction of the nanoparticles?
The continuous changed in θ with respect to time for the systems tested is an indication that the addition of a small fixed fraction of the nanoparticles to the dispersing fluid significantly impacted the fluid-rock interaction which led to efficient displacement of oil over time thus the rock surface is rendered more water-wet.
Q13. What was used to render the calcite crystals oil-wet?
Dodecyltriethoxysilane (C18H40O3Si, from Sigma Aldrich; purity >99.0 mol%; boiling point: 538.4k; Density: 875kg/m3 – Fig. 1) was used to render the calcite crystals oil-wet.
Q14. What is the effect of the salt concentration on the wettability of zirconium oxide?
zirconium oxide when compared to other nanoparticles demonstrate better wettability alteration efficiency at very minimal concentration (0.04 - 0.05wt%).
Q15. How did the change in the presence of NiO?
ZrO2 exhibited good wettability alteration efficiency: θ changed from an intermediate wet-state (90° in air) to waterwet (60°) in 3 wt% NaCl brine but remained intermediate-wet (81°) in the presence of NiO.
Q16. What is the effect of the wettability of the NiO nanofluids?
ZrO2 displayed a slightly better performance over NiO. After 300s in air, θ exhibited a small change, θ decreased from 90° to 76° for ZrO2 nanofluid, and to 82° for NiO nanofluids.
Q17. What was the initial test for water contact angles?
Reference tests for water contact angles (θ) were initially conducted on cleaned calcite crystals to ensure a completely water-wet state.
Q18. What is the effect of different formulations on the EOR?
the influence of diverse ZrO2 and NiO formulations was systematically examined in terms of wettability alteration efficiency and the nanoparticles potentials as EOR agents.
Q19. How much NaCl was used to determine the wettability of NiO nanoflui?
ZrO2 and NiO nanoparticles were at the (fixed) optimum nanoparticle concentration (0.05 wt%; chosen due to its effectiveness; see Fig. 4, 5 above) and at a fixed 7 wt% NaCl concentration.