Silica Nanofluids Research Articles

Rheological analysis and EOR potential of surfactant treated single-step silica nanofluid at high temperature and salinity

Single-step nanofluids have shown better stability and size control properties than conventional two-step nanofluids under similar conditions. However, for wide-spread oilfield acceptance, there is a need to investigate the role of oilfield conditions viz., temperature, salt and pH on stability of single-step nanofluids. Thus, in this study, single-step silica nanofluids were synthesized in base fluid (1000 ppm polyacrylamide, PAM) and their stability was investigated using methods such as dynamic light scattering (DLS) and rheological analysis to establish their viability as suitable enhanced oil recovery (EOR) agents. PAM is a widely used oilfield practically applicable polymer. Primarily, the single-step silica nanofluids were found to destabilize at higher temperatures (≥90 °C) due to thermal stability issues of PAM at high temperatures. This was also understood by PAM rheology. The inclusion of salt reduced the stability of nanofluids due to the suppression of inter-particle repulsive forces. The variation in pH also influenced nanofluid stability and pH range of 8–10 was observed for the stable behavior of nanofluids. The addition of an anionic surfactant (SDS) improved nanofluid stability by reducing salt-induced NP agglomeration; increasing surfactant concentration initially improved nanofluid resistance to salt induced agglomeration and at high surfactant concentrations, the nanofluids exhibited greater NP agglomeration even in the absence of salt. The oil recovery results also showed that surfactant use in the synthesis of silica nanofluid for oil recovery applications may provide better results than sole silica nanofluid. Based on the observations, surfactant treated single-step silica nanofluid use was found favorable for oilfield practices where conventional nanofluids may show challenges.

Impact of anionic surfactant on stability, viscoelastic moduli, and oil recovery of silica nanofluid in saline environment

Controlling nanofluid stability in saline environment has been a long-standing challenge as salt ions screen-out the surface charge of the nanoparticles (NPs), rendering them unstable. This study thus reports the use of an anionic surfactant (sodium dodecylsulfate, SDS), as co-stabilizer, that not only controls the effect of salt, but also dramatically improves nanofluid stability by controlling the agglomeration rate. Silica NPs of 0.5 wt%, SDS with concentration ≥ critical micelles concentration (CMC), and polymer polyacrylamide (PAM) of 1000 ppm were used while the concentration of NaCl was explored up to 5 wt%. The dispersion stability of nanofluid without salt (NaCl) was found to be ~4 weeks which further increased to ~7 weeks with increasing SDS concentration. With increasing SDS (>CMC), a reduction in NP agglomeration was observed that delayed the NP settlement. The effect of salinity was also investigated for flow properties of nanofluids and, an unstable rheological response (transition from viscoelastic to viscous) was observed with increasing NaCl concentration. However, SDS (>CMC) made nanofluid rheologically stable up to saline environment of 3 wt%, an optimum salinity was identified. SDS role on nanofluid stabilization in saline environment is also generalized for enhanced oil recovery (EOR) applications in a porous media enriched with varying salinity. With increasing salinity, the cumulative oil recovery from sand-pack reduced and reached to minimum level of 48% original oil in place (OOIP) at 3 wt% NaCl which was 58% OOIP without salinity. Oil recovery re-established to 55% OOIP in presence of increasing SDS concentration, which is remarkable for nanofluid applicability in saline environment where conventional methods typically show challenges. Even in the presence of 4 wt% NaCl, the synergy between surfactant and nanofluid enabled an improvement in oil recovery and subdued surfactant adsorption in both unconsolidated and consolidated porous media, paving future way for field implementation.

Influence of (3–Aminopropyl) triethoxysilane on silica nanoparticle for enhanced oil recovery

A substantial volume of oil is trapped in the reservoir after the primary and secondary recovery processes because of pressure and reservoir heterogeneity. Experimental results have indicated that silica nanoparticle (SNP) flooding is highly efficient in enhanced oil recovery (EOR). The performance is a function of preparation and modification processes. The use of SNP modified by (3–Aminopropyl) triethoxysilane (APTES) is yet to be extensively examined for potential use in EOR. In this study, a modified SNP was examined to determine its influence in EOR applications. Sessile drop technique was utilized to determine the effectiveness of the modified SNP in altering the wettability of the oil-wet sandstone core. Subsequently, the interfacial tension (IFT) between oil and water was also investigated. Furthermore, the oil displacement efficiency of the modified nanofluid was compared with the unmodified. Zeta potential (ζ–potential), Fourier transform infrared spectrometry (FTIR), field emission scanning electron microscope (FESEM), and energy dispersive X–ray (EDX) spectra were used to confirm the modification of the SNP. The results show that APTES adhered to the surface of the modified SNP, and the particles are finely dispersed and stable in aqueous solution. The ζ–potential indicates that the surface charge of the particles increased from −16 mV to +26.4 mV after modification, which indicates long term stability when used in EOR processes. The silica nanofluids (SNFs) altered the wettability of sandstone core from oil–wet at a contact angle of 134.7° to water–wet at a contact angle of 54.3° (modified SNF) and 54.5° (unmodified SNF), at low concentrations. Also, the IFT of the modified SNF was low compared to unmodified SNF and APTES. The oil recovery of water flooding showed 62.9% and it improved to 75% and 69.6% when modified and unmodified SNFs were used, respectively. The pressure drop of the modified SNF was higher compared to the unmodified SNF which confirmed the stability of the modified SNF. Thus, the SNFs were very efficient in mobilizing trapped oil at ambient conditions and is, therefore, recommended for EOR processes.

Analysis of thermal-hydraulic performance and flow structures of nanofluids across various corrugated channels: An experimental and numerical study

The combination of nanofluid and corrugated surface is regarded as a very cost-efficient strategy for providing high heat transfer performance between the target surface and working fluid in different heating and cooling system applications. Herein a comparison study is reported on the thermal performance of different corrugated channels using nanofluids under turbulent flow and constant heat flux conditions. Three shapes, namely, semicircle corrugated channel (SCC), trapezoidal corrugated channel (TCC), and straight channel (SC) are fabricated and tested with 1% and 2% volume fraction of SiO2-water and Al2O3-water nanofluids. Nanoparticles with a size of 20 nm dispersed in water with specific volume fractions are used for comparison and evaluation. The numerical simulations present the flow structures of nanofluids in terms of velocity, isotherms, turbulent viscosity, vorticity and turbulent kinetic energy contours. The findings show that the heat transfer and pressure drop increase as volume fractions of nanofluids and Reynolds number increase. The experiments also revealed that the use of modified channels significantly increases the heat transfer ratio and the greatest enhancement ratio was achieved through the use of a trapezoidal corrugated channel with ϕ=2% of silica nanofluid. Over ranges of considered flow, silica nanofluid was better than alumina nanofluid and the best thermal performance of 1.94 was recorded using silica nanofluid at ϕ=2% and TCC at Reynolds number of 10000. Additionally, new empirical correlations were proposed and reported based on experimental data.

Nanoscale investigation of silicon dioxide nanofluids and implications for enhanced oil recovery – An atomic force microscope study

The use of silica-based nanofluids in enhanced oil recovery (EOR) has received significant attention recently. Aqueous dispersion of silica nanoparticles (<100 nm) can improve oil recovery through wettability alteration via rock/fluid and fluid/fluid interactions. Silicon dioxide nanofluids also offer superior advantages such as controllable chemistry and environmental safety. The potential of these chemicals has been studied reasonably at larger scales through contact angle and force imbibition tests. However, there is inadequate scientific understanding of nanofluid EOR. Evidence of oil recovery at nanoscale is also limited, which is important for low-porosity and permeability petroleum rocks with nanopores. In this study, we conducted an atomic force microscopy (AFM) study to investigate the effect of silica-based nanofluids on wettability alteration in model sandstones at nanoscale. We used CH2- and C6H5- terminated functionalized AFM probes to represent saturated and aromatic crude oils (respectively), and quartz & feldspar minerals to represent model rock surfaces. Our results show that adhesion force between these non-polar moieties and minerals decrease with increasing nanofluid concentration. We demonstrate experimentally at nanoscale that silica nanofluids significantly reduces work of adhesion – a fundamental wettability indicator - between functionalized probes and substrates. Across all tests, we observed a threshold concentration of 0.5 wt% above which wettability is not improved. Our findings offer fresh insight into the fundamental investigations of oil release mechanism with dispersed nanoparticles and provide original evidence on the implications of nanofluid injection for enhanced oil recovery at sub-micron scale.

Single-step silica nanofluid for improved carbon dioxide flow and reduced formation damage in porous media for carbon utilization

Water-alternating gas (WAG) is affected by viscous fingering (with too much gas) and trapping of reservoir oil (with too much water) that can be addressed by advanced methods such as nanofluids, those not only increase CO2 capturing but also provide significant control on fingering. Therefore, this study reports the use of single-step silica nanofluids, of controllable nanoparticle (NP) size (below 100 nm), for improved CO2 flow and reduced formation damage in porous and permeable media. Polyacrylamide (PAM, 1000 ppm) was used as viscosifier and found favorable for enhanced dispersion stability (more than 2 months) in nanofluids. The parameters, such as amount of precursor (Tetraethylorthosilicate-TEOS) and catalyst (ammonium hydroxide-NH4OH), and amount of PAM were varied. Silica NPs were highly stable against agglomeration as reported by DLS, FTIR, TEM, SEM, and UV methods. Silica Nanofluids delayed CO2 breakthrough by retaining CO2 in sand-pack for longer duration than water/PAM. CO2 in presence of NPs made stable foam that was viscous and least mobile (than CO2) as confirmed by progressive increase in pressure while CO2 flow with water/PAM was unstable as pressure varied non-uniformly. This is of key importance for CO2 sequestration studies in porous reservoirs. Since NPs are solid substances, they can retain in sand-pack during nanofluid use for CO2 utilization strategies. NP retention was determined experimentally for different (1) sand-pack length, (2) flow rate, (3) NP concertation, and (4) test temperature. NP retention of only 8–12% of total injected amount was reported with Sand-pack length as the most influential variable.

CO2 capturing evaluation of single-step silica nanofluid through rheological investigation for nanofluid use in carbon utilization applications

Abstract Single-step silica nanofluids offer better stability and size-control due to less nanoparticle (NP) agglomeration. Uniform distribution and desired size of NP make nanofluid a rheologically modified fluid to be suitable for carbon utilization applications. Thus, in this work, single-step (sol-gel) technique is used to prepare silica nanofluids of different particle sizes (34–142 nm) in base of polyacrylamide (PAM, 1000 ppm). These nanofluids was tested for CO2 capturing applications using rheological measurements (shear and dynamic) as a function of different conditions [particle concentration = 0.1, 0.5, and 1 wt% and temperature = 303, 323, and 353 K]. Increasing particle size was found to affect rheological properties insignificantly while increasing particle concentration led to increment in viscosity and viscoelastic moduli (elastic: G′ and viscous: G″), good for nanofluid usage in oilfield practices where improved viscosity is required for higher oil recovery. The inclusion of CO2 made nanofluid lighter and thus, viscosity and moduli values slightly reduced for CO2 laden nanofluids. The effect of high temperature (353 K) on capturing potential of nanofluids was found marginal as viscosity and viscoelastic properties and their flow trends remained almost similar at each test temperature, which indicates CO2 capturing into the networks of NP and PAM was intact and even temperature could not deform it. However, a slight reduction in viscosity and moduli of nanofluids was attributed to temperature effect on PAM rheology. Thus, the synthesized nanofluids behaved almost thermally stable and showed marginal effects of flow conditions (shear rate, amplitude, and frequency) on rheological properties and CO2 capturing potential of silica nanofluids, which is of key importance for various applications where conditions differ on a large scale.

Experimental Study on the Viscosity Behavior of Silica Nanofluids with Different Ions of Electrolytes

Understanding the mechanisms behind the interaction between the nanoparticles (NPs) and the brine/seawater is critical for successful oil recovery. In this study, the effect of ionic components of ...

Evaluation of Silica Nanofluids in Static and Dynamic Conditions by an Optical Fiber Sensor.

This work presents an optical fiber dynamic light scattering sensor capable of simultaneously assessing concentration and flow speed of nanofluids. Silica nanoparticles (189 nm) in water were tested, yielding a sensitivity of 0.78288 × 10³ s−1 for static conditions. Then, the sensor was submitted to situations that simulate spatial concentration changes, offering better results than those obtained by traditional mathematical models. Finally, in flow tests, the light backscattered by the nanoparticles were collected by a fiber probe placed parallel to the streamline, whereas intensity values were processed by artificial neural networks. The sensor provides average errors of 0.09 wt% and 0.26 cm/s for concentration and speed measurements, respectively, and can be further applied to assess different types of nanofluids and inline processes.

Convective heat transfer studies in dilute alumina and silica nanofluids flowing through a channel using Mach-Zehnder interferometry

Convective heat transfer in dilute oxide nanofluids flowing through a channel was measured using the Mach-Zehnder interferometry, a non-intrusive measurement technique. The convective performance of two different concentrations (0.01 and 0.02 vol.%) of alumina and silica nanofluids were studied and compared with that of de-ionized (D.I) water. In the present work, fringe analysis based on Naylor and Duarte method, with appropriate modifications for liquids was used to measure the local heat transfer coefficients along the channel. Studies have previously been reported only on the effects of Reynolds number in the channel flow, at a single heat input. In the present work, experiments were conducted at a constant Reynolds number (200), for six different heat inputs in the range of 5 W to 30 W. At 30 W, the enhancement in average heat transfer coefficient for 0.02 vol.% alumina nanofluid was 15.9 ± 4.1%, while, 0.02 vol.% silica nanofluid showed a decrement of 11.9 ± 2.9% compared to D.I water. Silica nanofluids were found performing inferior to D.I water and alumina nanofluids for all heat inputs. The variations in the trend for silica nanofluids are explained in the light of thermophoretic effects, Brownian motion and disruption of boundary layer.

Wettability alteration of calcite and dolomite carbonates using silica nanoparticles coated with fluorine groups

Altering the wettability of a gas-liquid system from liquid-wetting to intermediate gas-wetting is a novel strategy for removing condensate from gas condensate reservoirs. In this paper, the role of a silica nanofluid modified by fluorine groups in the wettability alteration of seven carbonate samples was investigated. An acid test and Energy Dispersive X-ray Spectroscopy analysis were carried out to identify the levels of calcite and dolomite as dominant carbonate minerals and evaluate the coating ability of the proposed chemical used on carbonate surfaces. Contact angle measurements and spontaneous imbibition experiments were conducted before and after wettability alteration. In addition, gas flooding experiments were conducted on three permeable core samples to investigate the effect of the nanofluid on the fluid flow at the core scale. Contact angle measurements demonstrated that the wetting tendency of core samples altered from liquid-wetting into gas-wetting after surface treatment, and a higher contact angle was achieved for carbonate cores with less dolomite than calcite. EDX analysis showed more fluorine and silica adsorption on calcite, compared to dolomite cores. After surface modification, the brine imbibed into carbonate core samples 1 to 7 decreased by 0.104, 0.174, 0.0016, 0.773, 0.355, 0.056, and 0.279, respectively. Core flooding results demonstrated that the recovery factor of three permeable core samples increased from 56.52%, 49.69%, and 65.33%–69.34%, 56.75%, and 76.72%, respectively.

Simulation of pool boiling of nanofluids by using Eulerian multiphase model

In the present work, a new simulation of nanofluid/vapor two-phase flow inside the 2-D rectangular boiling chamber was numerically investigated. The Eulerian–Eulerian approach used to predict the boiling curve and the interaction between two phases. The surface modification during pool boiling of silica nanofluid represented by surface roughness and wettability is put into the account in this simulation. New closure correlations regarding the nucleation sites density and bubble departure diameter during boiling of silica nanofluid were inserted to extend the boiling model in this work. Besides, the bubble waiting time coefficient which involved in quenching heat flux under heat flux partitioning HFP model was corrected to improve the results of this study. The numerical results validated with experimental works in the literature, and they revealed good agreements for both pure water and nanofluids. The results found that when improving the heat flux partitioning model HFP by considering the surface modification of nucleate pool boiling parameters, it will give more mechanistic sights compared to the classical model, which is used for predicting of boiling heat transfer of pure liquid.

Evaluating the potential of surface-modified silica nanoparticles using internal olefin sulfonate for enhanced oil recovery

Recently, nanoparticles have proven to enhance oil recovery on the core-flood scale in challenging high-pressure high-temperature reservoirs. Nanomaterials generally appear to improve oil production through wettability alteration and reduction in interfacial tension between oil and water phases. Besides, they are environmentally friendly and cost-effective enhanced oil recovery techniques. Studying the rheological properties of nanoparticles is critical for field applications. The instability of nanoparticle dispersion due to aggregation is considered as an unfavorable phenomenon in nanofluid flooding while conducting an EOR process. In this study, wettability behavior and rheological properties of surface-treated silica nanoparticles using internal olefins sulfonates (IOS20–24 and IOS19–23), anionic surfactants were investigated. Surface modification effect on the stability of the colloidal solution in porous media and oil recovery was inspected. The rheology of pure and surface-treated silica nanoparticles was investigated using a HPHT rheometer. Morphology and particle size distributions of pure and coated silica nanoparticles were studied using a field emission scanning electron microscope. A series of core-flood runs was conducted to evaluate the oil recovery factor. The coated silica nanoparticles were found to alter rheological properties and exhibited a shear-thinning behavior as the stability of the coated silica nanoparticles could be improved considerably. At low shear rates, the viscosity slightly increases, and the opposite happens at higher shear rates. Furthermore, the surface-modified silica nanoparticles were found to alter the wettability of the aqueous phase into strongly water-wet by changing the contact angle from 80° to 3° measured against glass slides representing sandstone rocks. Oil–water IFT results showed that the surface treatment by surfactant lowered the oil–water IFT by 30%. Also, the viscosity of brine increased from 0.001 to 0.008 Pa s by introducing SiO2 nanoparticles to the aqueous phase for better displacement efficiency during chemical-assisted EOR. The core-flood experiments revealed that the ultimate oil recovery is increased by approximately 13% with a surfactant-coated silica nanofluid flood after the conventional waterflooding that proves the potential of smart nanofluids for enhancing oil recovery. The experimental results imply that the use of surfactant-coated nanoparticles in tertiary oil recovery could facilitate the displacement efficiency, alter the wettability toward more water-wet and avoid viscous fingering for stable flood front and additional oil recovery.

Solvent-free ionic silica nanofluids: Smart lubrication materials exhibiting remarkable responsiveness to weak electrical stimuli

Solvent-free ionic nanofluids (NFs) are promising smart lubrication materials due to their remarkable stimuli responsiveness to an external electric field. In this study, four kinds of silica (SiO2) NFs with diverse corona molecule structures were successfully synthesized. Effects of NFs’ structures on their physic-chemical properties and lubricity were investigated. In particular, nanostructures of the tribofilms were comprehensively characterized for shedding light on lubricating mechanisms of the NFs. Our results demonstrate that the newly synthesized NFs exhibit excellent lubrication performance and their lubricity displays remarkable electrical responsiveness. Applying even a rather low electrical potential, e.g. 1.5 V, gives rise to significant and immediate friction reduction. Moreover, lubricity and electrical responsiveness of the NFs are closely dependent on structures of the corona layers. Interestingly, our work provides direct evidence that feeding NFs onto the friction zone expedites growth of a robust tribofilm consisting mainly of SiO2 nanoparticles and tribochemical products. This work opens up new opportunities for tuning structures and functionalities of boundary layers of numerous motion components by tailoring architectures of NFs and controlling the electrical stimuli.

Turbulent convective heat transfer of silica oxide nanofluid through corrugated channels: An experimental and numerical study

Combining a corrugated surface and nanofluids technologies have caused attracted significant interest to develop the ability of compact heat exchangers in order to produce more efficient and reliable thermal systems. In this paper, the forced convective turbulent flow of SiO2-water nanofluid through different corrugated channels is studied numerically and experimentally. All studies are performed for the straight channel (SC) and different two corrugated channels, namely semicircle corrugated channel (SCC) and trapezoidal corrugated channel (TCC) over Reynolds number ranges of 10000–30000. SiO2 nanoparticles suspended in distilled water with two particle volume fractions (1% and 2%) were successfully prepared and tested. Numerically, the discussion and analysis on heat transfer and flow characteristics which including velocity, isotherms contours, turbulence kinetic energy, vortices magnitude are provided. The results show that the corrugation profile has a significant impact on heat transfer enhancement compared to the straight profile. Also, silica nanofluid shows a better heat transfer in comparison with the base fluid. The new style of trapezoidal corrugated channel offers the best heat transfer enhancement. This indicated that this geometry with silica nanofluid can improve the heat transfer significantly with a reasonable increase in pressure drop. The results for the numerical outcomes and experimental data are in good agreement.

Insights into stability of silica nanofluids in brine solution coupled with rock wettability alteration: An enhanced oil recovery study in oil-wet carbonates

Stability of nanoparticle dispersion in brine solution is a key parameter for a successful nanofluid- based enhanced oil recovery processes. This paper aims to provide a systematic laboratory study to investigate the stability of silica nanoparticles (NPs) in presence of mono and divalent salts, namely NaCl and MgCl2, coupled with their potential to alter wettability of low-permeable, oil-wet carbonates at 80 °C. First, silica nanofluids with different salt concentrations were prepared using sonication process. Results showed that presence of divalent cations significantly hinders the stability of silica nanofluids as compared to monovalent ones. It was found that most of silica NPs was precipitated in presence MgCl2 even at a low concentration of 2000 ppm while no particle precipitation was observed with 10,000 ppm NaCl over a two- week period. This was in line with a smaller particle size of silica NPs with 10,000 ppm NaCl (73 nm) as compared to MgCl2, 388 nm. Also, we found a noticeable reduction in zeta potential of silica nanofluids with MgCl2, −8 mV, as compared to NaCl, −25 mV. This reveals that the negative surface charge of silica NPs became more neutralized in presence of MgCl2 and thus more chance for agglomeration of silica NPs through the aqueous phase. As to rock- nanofluid interaction, silica nanofluids in presence of NaCl exhibited a higher potential to alter rock wettability to more water-wetness than MgCl2. Such wettability alteration was discussed in terms of adsorption of silica NPs on the carbonate rock followed by a generation of thin layer of silica NPs on the rock surface, leading to an extra pressure on oil droplet. This was in line with SEM- EDX analyses indicting that silica NPs covers the carbonate rock surface. In terms of oil recovery, imbibition of silica nanofluid containing 10,000 ppm NaCl provided 14% incremental oil while the lowest oil recovery was obtained for silica nanofluids containing MgCl2 due to their less stability. These results showed that there could be a correlation between the stability of silica nanofluids and their EOR potential, which is strongly dependent on the salt type and concentration.

Enhancement of nanofluid heat transfer in a mini-tube using SiO2 nanoparticles

ABSTRACTThis study is aimed to investigate the effect of SiO2/distilled (DI) water nanofluids on the heat transfer enhancement inside a circular mini-tube tube with an inner diameter (Di) = 0.8 mm. The flow was run at fully laminar flow with Reynolds number (Re) = 112. The initial temperatures at all channels were maintained at 50°C as uniform heat flux was applied to the outer surface of the mini-tube. Different weight concentrations (wt%) of silica/water nanofluids (0.1, 0.2, 0.3, 0.4, 0.5 wt%) were used in the experiment. The results concluded that the heat transfer coefficient and Nusselt number were significantly enhanced using silica nanofluids as compared to distilled water as heat transfer fluids. Higher values of heat transfer coefficient and Nusselt number indicate that more heat is being transferred from the tube to the fluid which results in a significant reduction of the overall outer tube surface temperature. The heat transfer enhancement was found to be dependent on the nanoparticle concentrations. The maximum heat transfer coefficient of the nanofluids was achieved using 0.5% silica nanofluids at axial location (Z/Di) = 51.25 with a value of 257.14 W/m2.K.

Reversible and irreversible adsorption of bare and hybrid silica nanoparticles onto carbonate surface at reservoir condition

Realistic implementation of nanofluids in subsurface projects including carbon geosequestration and enhanced oil recovery requires full understanding of nanoparticles (NPs) adsorption behaviour in the porous media. The physicochemical interactions between NPs and between the NP and the porous media grain surface control the adsorption behavior of NPs. This study investigates the reversible and irreversible adsorption of silica NPs onto oil-wet and water-wet carbonate surfaces at reservoir conditions. Each carbonate sample was treated with different concentrations of silica nanofluid to investigate NP adsorption in terms of nanoparticles initial size and hydrophobicity at different temperatures, and pressures. Aggregation behaviour and the reversibility of NP adsorption onto carbonate surfaces was measured using dynamic light scattering (DLS), scanning electron microscope (SEM) images, energy dispersive X-ray spectroscope (EDS), and atomic force microscope (AFM) measurement. Results show that the initial hydrophilicity of the NP and the carbonate rock surface can influence the NPs adsorption onto the rock surfaces. Typically, oppositely charged NP and rock surface are attracted to each other, forming a mono or multilayers of NPs on the rock. Operation conditions including pressure and temperature have shown minor influence on nano-treatment efficiency. Moreover, DLS measurement proved the impact of hydrophilicity on the stability and adsorption trend of NPs. This was also confirmed by SEM images. Further, AFM results indicated that a wide-ranging adsorption scenario of NPs on the carbonate surface exists. Similar results were obtained from the EDS measurements. This study thus gives the first insight into NPs adsorption onto carbonate surfaces at reservoirs conditions. High pressure/temperature cell for surface treatment with nanoparticles (nanofluid) at reservoir condition.

Effects of silica nanoparticles and low concentration on the deterioration of critical heat flux in a pool boiling experiment with a flat-type heater

An evaluation of nanoparticle size effects on the critical heat flux (CHF) was conducted through pool boiling experiments under atmospheric pressure in low concentration regions from 0.1 to 10 ppmv. A smooth flat-type heater made of stainless steel was used as a test section. Silica nanofluids were prepared by sonication processes to guarantee stability using various sizes of silica nanoparticles (8, 15, 65, and 400 nm). In the experiments, we observed the CHF enhancement at high concentration regardless of particle size. However, the deterioration of the CHF was observed in the relatively low concentration regions with particles that were smaller than 100 nm. Furthermore, when the particle size decreased, the CHF values appeared to be higher at the high concentration of 10 ppmv. On the other hand, for large particles with a size of 400 nm, no deterioration of the CHF at low concentrations was observed. The boiling time, which is considered to affect the nanoparticle deposition, had marginal influences on CHF values. Based on the CHF trends, surface analyses with heaters after the experiments were conducted through SEM images, and contact angles and roughness values were used to evaluate the surface characteristics modified by nanoparticle deposition. Furthermore, in this study, the discussions on the particle size effects and deterioration of the CHF, and also its enhancement, are included based on the behavior of the structural disjoining pressure, nucleation site density, and porous layer as a function of the nanoparticle size and concentration.

Influence of Individual Ions on Silica Nanoparticles Interaction with Berea Sandstone Minerals

Nanofluids are prepared by dispersing silica nanoparticles in aqueous media (brines). The purpose of this work is to address brine/rock interactions in presence of nanoparticles. Our previous studies have shown that silica nanofluids are effective in reducing formation damage in sandstone reservoirs. This study addresses effect of individual ions on dispersed silica nanoparticles’ interaction with Berea Sandstone minerals. The selected ions are Mg2+, SO42− and Na+, in MgCl2, Na2SO4 and NaCl, which are the major constituents of seawater. Three flooding stages for Berea Sandstone cores were followed. The first flooding stage was without nanoparticles, the second one was a slug of the nanoparticles with tracer and the third stage was a post-flushing of the core with the respective ion. The effluent tracer concentration, nanoparticle content, ion concentrations and pH reflect the effect of individual ions on nanoparticle/mineral interaction which were used for suggesting possible interaction mechanisms. Presence of Mg2+ and SO42− ions improved the adsorption of nanoparticles on minerals, however the effect of Na+ was lesser. In general, in all the cases nanoparticles reduced the mineral dissolution and associated fine migration/possible formation damage.