Browsing by Subject "Emulsion"

Now showing 1 - 11 of 11

Assembly of colloidal nanocrystals into phospholipid structures and photothermal materials
(2012-08) Rasch, Michael; Korgel, Brian Allan, 1969-
There has been growing interest in developing colloidal metal and semiconductor nanocrystals as biomedical imaging contrast agents and therapeutics, since light excitation can cause the nanocrystals to fluoresce or heat up. Recent advances in synthetic chemistry produced fluorescent 2-4 nm diameter silicon and 1-2 nm diaemeter CuInSSe nanocrystals, as well as 16 nm diameter copper selenide (Cu₂₋[subscript x]Se) nanocrystals exhibiting strong absorbance of near infrared light suitable for biomedical applications. However, the syntheses yield nanocrystals that are stabilized by an adsorbed layer of hydrocarbons, making the nanocrystals hydrophobic and non-dispersible in aqueous solution. Encapsulating these nanocrystals in amphiphilic polymer micelles enables the nanocrystals to disperse in water. Subsequently, the Si nanocrystals were injected into tissue to demonstrate fluorescence imaging, the photothermal transduction efficiency of copper selenide nanocrystals was characterized in water, and the copper selenide nanocrystals were used enhance the photothermal destruction of cancer cells in vitro. The polymer-encapsulated copper selenide nanocrystals were found to have higher photothermal transduction efficiency than 140 nm diameter Au nanoshells, which have been widely investigated for photothermal therapy. Combining the optical properties of metal and semiconductor nanocrystals with the drug-carrying capability of lipid vesicles has received attention lately since it may create a nanomaterial capable of performing simultaneous drug delivery, optical contrast enhancement, and photo-induced therapy. Hydrophobic, dodecanethiol-coated Au nanocrystals were dispersed in water with phosphatidylcholine lipids and characterized using cryo transmission electron microscopy. 1.8 nm diameter Au nanocrystals completely load the bilayer of unsaturated lipid vesicles when the vesicles contain residual chloroform, and without chloroform the nanocrystals do not incorporate into the vesicle bilayer. 1.8 nm Au nanocrystals dispersed in water with saturated lipids to form lipid-coated nanocrystal agglomerates, which sometimes adhered to vesicles, and the shape of the agglomerates varied from linear nanocrystal chains, to flat sheets, to spherical clusters as the lipid fatty acid length was increased from 12 to 18 carbons. Including squalene formed lipid-stabilized emulsion droplets which were fully loaded with the Au nanocrystals. Results with 4.1 nm Au and 2-3 nm diameter Si nanocrystals were similar, but these nanocrystals could not completely load the bilayers of unsaturated lipids.
Carbon dioxide mobility and sweep alteration using surface-coated silica nanoparticles
(2019-08-14) Alfakher, Ahmad; DiCarlo, David Anthony, 1969-
Solvent flooding is a well-established method of enhanced oil recovery (EOR), CO₂ being the solvent most often used. CO₂ has also been injected into saline aquifers as a method of storage in an application of Carbon Capture and Storage (CCS). Both applications suffer from poor sweep efficiency. Creating in-situ CO₂ foam has previously been shown to improve the sweep efficiency of CO₂ floods. This study tested the use of surface-coated silica nanoparticles as an in-situ CO₂ foaming agent. In each experiment, the pressure drop was measured in five separate sections in the core, as well as along the whole core. In addition, the saturation in the core was measured periodically using a CT scanner. The experiments consisted of vertical core floods where liquid CO₂ displaced brine from the top to the bottom of the core, comparing the results in cases where surface-coated silica nanoparticles were suspended in the brine to cases with no nanoparticles. Pressure drop readings were analyzed to exclude capillary effects and calculate relevant flow parameters, such as CO₂ mobility. In these experiments, the mobility of CO₂ was on average 89% less in floods with nanoparticles compared to floods with no nanoparticles. This reduction in mobility was found to be long-lasting. Breakthrough occurred 45% later in foamed CO₂, and the final CO₂ saturation was also 45% greater than with un-foamed CO₂. The new measurements and mobility calculations in this study show how nanoparticles stabilize the CO₂ front. They can also be used to upscale the behavior observed from the core-scale to the reservoir scale
Development and evaluation of enzymatically-degradable hydrogel microparticles for pulmonary delivery of nanoparticles and biologics
(2012-12) Wanakule, Prinda 1985-; Roy, Krishnendu
The emerging class of biologic drugs, including proteins, peptides, and gene therapies, are widely administered by injection, despite potential systemic side effects. Rational design of targeted carriers that can be delivered non-invasively, with reduced side effects, is essential for the success of these therapies, as well as for the improvement of patient compliance and quality of life. One potential approach is to take advantage of specific physiological cues, such as enzymes, which would trigger drug release from a drug carrier. Enzymatic cleavage is highly specific and could be tailored for certain diseased tissues where specific enzymes are up regulated. Enzymatically-degradable hydrogels, which incorporate an enzyme- cleavable peptide into the network structure, have been extensively reported for releasing drugs for tissue engineering applications. These studies showed that a rapid response and corresponding drug release occurs upon enzyme exposure, whereas minimal degradation occurs without enzyme. Recently, Michael addition reactions have been developed for the synthesis of such enzymatically-degradable hydrogels. Michael addition reactions occur under mild physiological conditions, making them ideally suited for polymerizing hydrogels with encapsulated biologic drugs without affecting its bioactivity, as in traditional polymerization and particle synthesis. The focus of my research was to create enzymatically-degradable hydrogel microparticles, using Michael addition chemistry, to evaluate for use as an inhalable, disease-responsive delivery system for biologic drugs and nanoparticles. In this dissertation, I utilize bioconjugation and Michael addition chemistries in the design and development of enzymatically-degradable hydrogels, which may be tailored to a multitude of disease applications. I then introduce a new method of hydrogel microparticle, or microgel, synthesis known as the Michael Addition During Emulsion (MADE) method. These microgel carriers were evaluated in vitro, and found to exhibit triggered release of encapsulated biologic drugs in response to enzyme, no significant cytotoxic effects, and the ability the avoid rapid clearance by macrophages. Lastly, in vivo studies in mice were conducted, and microgels were found to exhibit successful delivery to the deep lung, as well as prolonged pulmonary retention after intratracheal aerosol delivery. In conclusion, a new class of enzymatically-degradable microgels were successfully developed and characterized as a versatile and promising new system for pulmonary, disease-responsive delivery of biologic drugs.
Enhanced oil recovery of heavy oils by non-thermal chemical methods
(2013-05) Kumar, Rahul, active 2013; Mohanty, Kishore Kumar
It is estimated that the shallow reservoirs of Ugnu, West Sak and Shraeder Bluff in the North Slope of Alaska hold about 20 billion barrels of heavy oil. The proximity of these reservoirs to the permafrost makes the application of thermal methods for the oil recovery very unattractive. It is feared that the heat from the thermal methods may melt this permafrost leading to subsidence of the unconsolidated sand (Marques 2009; Peyton 1970; Wilson 1972). Thus it is necessary to consider the development of cheap non-thermal methods for the recovery of these heavy oils. This study investigates non-thermal techniques for the recovery of heavy oils. Chemicals such as alkali, surfactant and polymer are used to demonstrate improved recovery over waterflooding for two oils (A:10,000cp and B:330 cp). Chemical screening studies showed that appropriate concentrations of chemicals, such as alkali and surfactant, could generate emulsions with oil A. At low brine salinity oil-in-water (O/W) emulsions were generated whereas water-in-oil (W/O) emulsions were generated at higher salinities. 1D and 2D sand pack floods conducted with alkali surfactant (AS) at different salinities demonstrated an improvement of oil recovery over waterflooding. Low salinity AS flood generated lower pressure drop, but also resulted in lower oil recovery rates. High salinity AS flood generated higher pressure drop, high viscosity emulsions in the system, but resulted in a greater improvement in oil recovery over waterfloods. Polymers can also be used to improve the sweep efficiency over waterflooding. A 100 cp polymer flood improved the oil recovery over waterflood both in 1D and 2D geometry. In 1D geometry 1PV of polymer injection increased the oil recovery from 30% after waterflood to 50% OOIP. The tertiary polymer injection was found to be equally beneficial as the secondary polymer injection. It was also found that the combined application of AS and polymer did not give any major advantage over polymer flood or AS flood alone. Chemical EOR technique was considered for the 330cp oil B. Chemical screening studies showed that microemulsions could be generated in the system when appropriate concentrations of alkali and surfactant were added. Solubilization ratio measurement indicted that the interfacial tension in the system approached ultra-low values of about 10-3 dynes/cm. The selected alkali surfactant system was tested in a sand pack flood. Additionally a partially hydrolyzed polymer was used to provide mobility control to the process. The tertiary injection of ASP (Alkali-Surfactant-Polymer) was able to improve the oil recovery from 60% OOIP after the waterflood to almost 98% OOIP. A simple mathematical model was built around viscous fingering phenomenon to match the experimental oil recoveries and pressure drops during the waterflood. Pseudo oil and water relative permeabilities were calculated from the model, which were then used directly in a reservoir simulator in place of the intrinsic oil-water relative permeabilities. Good agreement with the experimental values was obtained. For history matching the polymer flood of heavy oil, intrinsic oil-water relative permeabilities were found to be adequate. Laboratory data showed that polymer viscosity is dependent on the polymer concentration and the effective brine salinity. Both these effects were taken into account when simulating the polymer flood or the ASP flood. The filtration theory developed by Soo and Radke (1984) was used to simulate the dilute oil-in-water emulsion flow in the porous media when alkali-surfactant flood of the heavy oil was conducted. The generation of emulsion in the porous media is simulated via a reaction between alkali, surfactant, water and heavy oil. The theory developed by Soo and Radke (1984) states that the flowing emulsified oil droplets clog in pore constrictions and on the pore walls, thereby restricting flow. Once captured, there is a negligible particle re-entrainment. The simulator modeled the capture of the emulsion droplets via chemical reaction. Next, the local water relative permeability was reduced as the trapping of the oil droplets will reduce the mobility of the water phase. This entrapment mechanism is responsible for the increase in the pressure drop and improvement in oil recovery. The model is very sensitive to the reaction rate constants and the oil-water relative permeabilities. ASP process for lower viscosity 330 cp oil was modeled using the UTCHEM multiphase-multicomponent simulator developed at the University of Texas at Austin. The simulator can handle the flow of three liquid phases; oil, water and microemulsion. The generation of microemulsion is modeled by the reaction of the crude oil with the chemical species present in the aqueous phase. The experimental phase behavior of alkali and surfactant with the crude oil was modeled using the phase behavior mixing model of the simulator. Oil and water relative permeabilities were enhanced where microemulsion is generated and interfacial tension gets reduced. Experimental oil recovery and pressure drop data were successfully history matched using UTCHEM simulator.
Experimental analysis of evaporation driven emulsion flow in porous media
(2013-05) Kulkarni, Akhil; Berberoglu, Halil
In some configurations of compact, biofilm based photobioreactors, algae grow on a porous substrate that acts as the support system for the cells providing them with the necessary water and nutrients as well as carrying away their secreted products. The flow in these porous media can be driven by evaporation, mimicking the function of a synthetic leaf. The surface properties of the porous medium as well as the presence of a second immiscible phase in the fluid transported can significantly alter the transport capability and evaporative performance of the porous medium. The focus of this study is to investigate these effects through an experimental study. A dilute, 1% emulsion of lauric acid (chemical formula: C₁₂H₂₄O₂) in water was prepared using Tween® 80 surfactant. Evaporation driven flow of deionized water and the emulsion through two porous media, a hydrophilic glass fiber membrane and a less hydrophilic poly(vinylidene) fluoride (PVDF) membrane were studied. Experiments were conducted to determine the effect of porous medium and fluid properties on the rate of evaporation. The parameters investigated were the hydrophilicity of the porous medium and the area of the porous medium available for evaporation for both water and emulsion. During the experiment, the mass flow rate of the fluid as well as the temperature and the relative humidity of the ambient air were monitored. The results showed that for dilute emulsions, the rate of evaporation observed was the same as that for water and was dictated by the governing laws of convection applicable to the situation based on the geometry of the setup and the ambient conditions. The response of the porous medium to flow of dilute emulsion showed that the highly hydrophilic glass fiber porous medium rejected any accumulation of the oil phase in the pores, and ejected it out, whereas the lesser hydrophilic PVDF porous medium allowed the pores to be clogged by the oil phase, resulting in change in the properties of the medium. However, the dependence of this observation solely on surface properties of the medium cannot be ascertained as the glass fiber medium had a larger pore diameter than the PVDF medium, and this factor could be of effect. The relative humidity of ambient air affected the rate of evaporation, which implied that the flow was limited by evaporation rather than by the viscous losses in the porous medium. The response of change in rate of evaporation to change in relative humidity showed a high time lag. Also, it was seen that there was a maximum area over which evaporation occurred which was dictated by the capillary pressure generated by the porous medium and the viscous losses for the fluid flow through the medium. Any excess area available for evaporation did not have any effect on the rate of evaporation. Electrospinning, as a simple and effective process for generating fibrous porous media was presented and a sample porous medium was prepared using this method. A parametric analysis of the effect of the potential difference applied between the syringe tip and the collector electrode, and the distance between the tip and the collector on the diameter of fibers produced, was performed.
Experimental evaluation of nanoparticles impact on displacement dynamics for water-wet and oil-wet porous media
(2015-08) Alghamdi, Abdullah Ali L; DiCarlo, David Anthony, 1969-; Bryant, Steven L
The potential of utilizing nanoparticles for production enhancement during oil-water displacement can play a significant role to achieve efficient and sustainable production of resources as they have shown great promise in stabilizing emulsion inside porous media. Furthermore, the displacement of brine solution containing nanoparticles by another non-wetting phase such as n-octane under water-wet condition has been shown to produce the signs of nanoparticle-stabilized emulsion. Because it is hypothesized that emulsion effects are caused by pore scale events that shear the fluids, this research aims to evaluate the impact of nanoparticles on different displacement scenarios (primary imbibition, primary drainage, secondary imbibition, and secondary drainage) and address the effect of wettability (oil-wet vs. water-wet), displacement types (different pore scale processes), and viscous stability (lower viscosity n-octane vs. higher viscosity tetradecane) on the generation of nanoparticle-stabilized emulsion in situ during immiscible displacement. Studying the impact of these changes is of primary importance since they contribute to changing pore scale events, fluids positioning and distribution, and displacement stability. Nanoparticle-stabilized emulsion has been associated with some indirect observable signs which include i) a rapid pressure drop increase exceeding the viscosity ratio between the brine and brine-nanoparticle dispersion, ii) a later breakthrough, , iii) a reduction in resident fluid residual saturation, and iv) a reduction of the invading phase endpoint relative permeability. Therefore, the impact of nanoparticles on the displacement was evaluated by measuring pressure drop data and effluent fluid histories. Those data were used to indicate the signs of nanoparticle-stabilized emulsion generation by interpreting pressure drop trends, water saturation histories, pressure drop ratio profile, residual fluid saturation, and endpoint relative permeability of the invading phase. Furthermore, the study attempts to examine the hypothesis that the displacement of a wetting hydrocarbon phase containing hydrophobic nanoparticles by another non-wetting aqueous phase will also generate nanoparticle-stabilized emulsion symptoms. This research reveals that compared to the control case (no nanoparticles), nanoparticles have the greatest effect on drainage type displacement (hydrocarbon invasion) with pressure drop reaching up to 500 % or even greater compared to the initial pressure drop observed at the start of the displacement. It also shows that those particles have little effect on imbibition displacement (aqueous phase invasion). This was found to be true for both oil-wet and water-wet despite the fact that fluids are configured differently at the pore-scale level. As for a more viscous hydrocarbon phase (tetradecane), the observed effects are generally lessened. As for secondary drainage displacement, initial trapping and the distribution of the hydrocarbon phase has also reduced the severity of the emulsion generation process. Based on the previous findings, an attempt to test the hypothesis of displacing hydrophobic nanoparticle dispersion by an aqueous brine solution under oil-wet condition was inconclusive due to the difficulty of maintaining stable hydrocarbon-nanoparticle dispersion. The displacement profile for all imbibition cases showed no significant differences between nanoparticle case and control case. Yet, we observe that nanoparticles have caused a reduction in the residual hydrocarbon saturation. This reduction was slightly greater for water-wet core compared to oil-wet. For these results I conclude that Haines jump and Roof snap-off may be one of the primary processes responsible to generate nanoparticle-stabilized emulsion during drainage displacement. However, observing emulsion symptoms during secondary drainage in oil-wet cores suggest either a) exact configuration is not important or b) possible alteration in the rock wettability by nanoparticles to produce the same configuration. The viscosity results suggest that nanoparticle effects have largely altered the conformance of the displacement. The presence of ethylene glycol and/or other coating chemicals used to maintain stability of nanoparticle dispersion may have caused the reduction of hydrocarbon phase residual saturation during all imbibition type displacement.
Generation and stabilization of emulsions and foams with nanoparticles and surfactants
(2015-12-03) Worthen, Andrew Jay; Johnston, Keith P., 1955-; Truskett, Thomas M; Bonnecaze, Roger T; Huh, Chun; Bryant, Steven L
Interactions between nanoparticles and surfactants are shown to improve the formation and stability of emulsions of dodecane-in-water and foams of carbon dioxide (CO2)-in-water. The initial work focuses on establishing a fundamental understanding of the interfacial properties of nanoparticle-surfactant combinations as novel dispersants for oil-in-water emulsions. Using the synergy between nanoparticles and surfactants, highly stable emulsions stabilized by with very low concentrations of amphiphiles are demonstrated. Additionally, amphiphilic polymers are grafted to nanoparticles to investigate their delivery to oil-water interfaces. Concepts developed in oil-in-water emulsion systems are then extended to design stabilizers for CO2-in-water foams. In this work, the first examples of viscous and opaque white foams stabilized solely with nanoparticles are demonstrated. This remarkable result was explained in terms of the nanoparticle interactions with the CO2 and water phases, which are tuned with small hydrophobic groups or amphiphilic polymers covalently grafted to the particle surfaces. Then the concept of nanoparticle-surfactant synergy is applied for the first time to CO2-in-water foams to create foams with both high stability and high viscosity. Finally, nanoparticles with grafted ligands on their surfaces are synthesized to give long-term colloidal stability in high salinity aqueous phases. These nanoparticles are then shown to improve CO2-in-water foam formation and stability. These new technologies may open new applications of nanoparticles in both seawater and reservoir brine.
Generation, stability, and transport of nanoparticle-stabilized oil-in-water emulsions in porous media
(2014-05) Gabel, Scott Thomas; Bryant, Steven L.; Huh, Chun
The ability of nanoparticles to stabilize oil/water emulsions provides many interesting opportunities for the petroleum industry. Emulsions can be used as a displacing fluid for enhanced oil recovery to improve sweep efficiencies. Emulsions can be used to improve conformance control by effectively blocking thief zones in reservoirs with a high degree of heterogeneity. As shown in this thesis emulsions can be used to deliver fluids that contact and mobilize residual oil. It is imperative to understand emulsion behavior in porous media for design purposes in enhanced or improved oil recovery processes involving emulsions. Nanoparticle-stabilized oil-in-water emulsions were continuously generated by co-injecting aqueous nanoparticle dispersion and oil through a beadpack. There exists a critical shear rate below which a stable emulsion will not be generated. The critical shear rate increased with decreasing bead size. Above the critical shear rate, the droplet size of the generated emulsion was a function of shear rate and decreased with increasing shear rate. The stable emulsions were characterized by their droplet size and rheology. The emulsion viscosity was highly dependent upon droplet size and not the bulk oil viscosity in the emulsion. The emulsions were highly shear thinning and emulsions with smaller droplets were more viscous than emulsions with larger droplets. Highly stable emulsions that were generated by co-injection were collected, separated from excess phase(s) and injected into beadpacks. In most experiments the injected emulsion coalesced into the bulk fluids. Whether the bulk fluids generated a new emulsion in the bead pack depended on the shear rate, bead size, and initial saturation of the beadpack. Different beadpack experiments showed the transition from one flow regime to a second flow regime as the slow movement of a coalescence/regeneration front propagated through the beadpack. Coreflood experiments confirmed the mechanisms hypothesized for the beadpack emulsion injection experiments. When a stable emulsion was injected the effluent emulsion rheology and droplet size were altered solely as a result of being forced through sandstone cores, not because of fluids contacted within the core. The shear rate controlled whether the emulsion coalesced and produced no effluent emulsion, regenerated into an emulsion with larger droplets, or regenerated into an emulsion with smaller droplets. Oil recovery experiments showed that nanoparticle-stabilized oil-in-water emulsion increased the recovery of oil compared to a waterflood for cores with immobile and mobile oil. The mechanism is the coalesced oil droplets form a flowing phase that is miscible with oil present in the core and thus achieves a much more efficient displacement. The possible continuous generation and coalescence of droplets may have increased the apparent viscosity, improving the sweep efficiency of the emulsion injection. A novel oil recovery mechanism was shown in imbibition experiments where nanoparticle dispersion was used to displace oil. Large shear rates coupled with the affinity for nanoparticles at the oil water interface enabled residual oil to be mobilized, or for residual oil blobs to spawn smaller droplets that are stabilized by the nanoparticles and thus can be transported with the dispersion through the core.
Nanoparticle stabilized oil-in-water emulsions for residual oil recovery
(2015-08) Ahmad, Yusra Khan; Daigle, Hugh; Huh, Chun
Transport of emulsions through porous media has the ability to play a significant role in many EOR processes. Nanoparticles can act as efficient emulsifying agents, producing emulsions that can improve sweep efficiencies leading to improved oil recoveries. This thesis has explored emulsion stability and flow through porous media whilst also assessing emulsion capabilities in residual oil recovery. Hydrophilic nanoparticle-stabilized oil-in-water emulsions of two different average droplet sizes were injected into hydrophobic beadpacks of varying bead size diameters. The smaller sized emulsion appeared to be more stable in its properties, more frequently being regenerated in the effluent in comparison to the larger droplet sized emulsion. With a decrease in bead diameter, the smaller droplet sized emulsion could not survive passage with regeneration. Smaller bead pack sizes also did not allow passage of the less stable emulsions with larger droplet sizes. The fastest emulsion regeneration was seen for emulsions with small droplet sizes through a beadpack of larger sized beads. Through the largest bead sized beadpack, small amounts of the less stable emulsion were seen to be regenerated but much later in the life of the experiment. Higher flow rates were able to regenerate emulsion for smaller droplet sizes but were unable to do so for the less stable larger sized emulsion. Pressure profiles appeared to similar for most runs where approximately the first 0-10 pore volumes show the greatest pressure buildup followed by what appears to be a more stable and slower increase in pressure. Coreflood experiments were performed to assess residual oil recovery for various oil-in-water emulsions. Higher percentage recoveries were seen to be dependent on a few leading factors. For more viscous, stable emulsions, it appeared that lower flow rates lead to higher percentage recoveries. At lower flow rates, no emulsion would also be produced in the effluent for the duration of the experiment. As pressure profiles were seen to increase throughout the experiment, attempted coalescence and regeneration were likely taking place. However, as regeneration was less successful, complete coalescence might be the reason for increased miscibility in the core, leading to higher recovery potentials. Encouraging recoveries were seen when a more viscous stable emulsion was used to recover residual oil less viscous than that of the continuous oil in the emulsion. Increasing the slug size of the emulsion injected helped recover more residual oil. Increasing the slug size however is only advantageous up till a limiting value where the injected emulsion slug would produce the same result as injected emulsion continuously through the sandstone core. Where enough emulsion was injected and therefore available inside the core, emulsion regeneration was seen. Lighter organic phases in emulsion form were used for oil recovery coreflood experiments. Similar to experiments performed with heavier organic phases in emulsion form i.e. mineral oil-in-water emulsion, octane-in-water emulsion was also not regenerated for low flow rates, completely coalescing inside the sandstone core. For higher flow rates, small amounts of octane emulsion were regenerated. In this case, similar to that of the mineral oil emulsion, increasing the flow rate seemed to have a negative effect on the percentage oil recovery. Surfactant stabilized octane-in-water emulsions showed the highest amount of percentage residual oil recovery. The pressure plot of these emulsions was different to those of nanoparticle stabilized emulsions where although the initial pressure increase matched up with the movement of the oil bank through the core, the latter part of the pressure profile appeared to decrease. This pressure profile was seen in both cases where the octane emulsion was injected into a fully brine saturated core as well as a core at residual oil saturation. It is interesting to note, however that surfactants by themselves are not capable of recovering any residual oil. It is only in emulsion form that this recovery is possible. Pentane-in-water emulsions were not seen to be stable for days unlike the other emulsions stated above. This was due to partial and continuous evaporation of pentane from the emulsion form at room temperature and pressure. When pressurized to 100 psi, however, the emulsion was seen to be stable for a number of days. All experiments were performed at high flow rates however emulsion was not seen to be regenerated in the effluent. This would suggest a lack of stability of the emulsion. Due to complete coalescence of the emulsion inside the core, miscibility would increase and this might be a reason for the higher percentage recoveries. Pressure profiles seemed to mimic all other oil-in-water emulsion injection experiments to sandstone cores at residual oil saturation.
Optimized heavy oil-in-water emulsions for flow in pipelines
(2016-05) Nizamidin, Nabijan; Pope, G. A.; Weerasooriya, Upali P; Mohanty, Kishore; Balhoff, Matthew; Bonnecaze, Roger
Oilfield operations such as drilling, reservoir management, and production require the injection and/or production of complex fluids to improve the extraction of crude oils. Some of these complex fluids such as drilling muds, fracking fluids, foams, emulsions, surfactants, and polymers, fall under the classification of colloidal suspensions which is one substance of microscopically dispersed insoluble particles suspended throughout another substance. These colloidal suspensions show complex rheological properties that are dependent on the suspension properties, flow conditions, and flow conduit dimensions. Rheology of colloidal suspensions is a complex subject that is still being investigated. The focus of this study is on heavy oil-in-water emulsions. Heavy oil and bitumen resources account for approximately 70% of the remaining oil discovered to date in the world. Heavy crude oils are costly to produce, transport, and refine compared to light crude oils due to the high viscosity of heavy crude oils. To improve the economic viability of producing heavy oils, especially in a time with low crude oil prices, operational expenses must be reduced. One of the main areas to improve is the cost associated with transporting produced heavy oils from production wells to refineries. Currently, heavy oils are diluted with low viscosity diluents such as condensates and light crude oils to lower the mixture viscosity below 350 cSt before heavy oils can be transported through pipelines. The diluted mixtures require up to 50% (vol.) diluents to lower the heavy oil viscosity. High demand and low supply of condensates and constrained pipeline capacities have resulted in pipeline transportation costs of up to $22/bbl of diluted heavy oil from Canada to refineries in the U.S. An alternative method of transporting heavy oils is to transport heavy oils in an emulsified form, heavy oil-in-water emulsions, which can show orders of magnitude lower viscosities compared to the viscosity of heavy oils. In this study, a simple, one-step method of preparing heavy oil-in-water emulsions was developed. The physical properties of heavy oil-in-water emulsions are controlled and modified by optimizing the chemical formulation used to prepare emulsions. Stable heavy oil-in-water emulsions can be prepared with chemical formulations that are tailored to the type of heavy oils and available water sources which can range from freshwater to softened seawater. The rheology of heavy oil-in-water emulsions has been characterized with a rotational viscometer. Heavy oil-in-water emulsions, especially concentrated emulsions, showed complex rheological properties such as shear thinning behavior, two-step yield stresses, two-step wall slips, and rheopexy. A rheological equation and a wall slip equation have been developed to model the rheology of heavy oil-in-water emulsions over a range of shear rates and flow conduit dimensions. Heavy oil-in-water emulsions characterized with capillary tube viscometers showed drastically different viscosity measurements compared to the viscosity measurements obtained with a rotational viscometer. This is important because the flow of emulsions in pipelines are similar to the flow of emulsions in capillary tube viscometers, not rotational viscometers. The lower viscosities measured with capillary tube viscometers are attributed to oil droplet migration away from the tube walls due to the shear heterogeneity observed in Poiseuille (tube) flow. A scaling equation was proposed to relate the viscosity measurements of emulsions with a rotation viscometer to the viscosity measurements of emulsions with capillary tube viscometers. The rheological measurements of heavy oil-in-water emulsions are used to estimate the flow of emulsions in crude oil pipelines with various radii. Viscosity measurements of optimized heavy oil-in-water emulsions with a rotational viscometer showed that heavy oil-in-water emulsions with up to 75% dispersed heavy oil can be successfully transported in crude oil pipelines. Adding the effect of oil droplet migration measured with capillary tube viscometers, heavy oil-in-water emulsions with up to 85-90% dispersed heavy oil can be successfully transported in crude oil pipelines. The cost of chemicals used to prepare 85% heavy oil-in-water emulsion is approximately $1-3/bbl of emulsion. Heavy oil-in-water emulsions also showed drag reduction properties which can significantly increase the maximum flow capacity of crude oil pipelines. Transporting heavy oils as concentrated heavy oil-in-water emulsions appeared to be a competitive if not a better method of lowering heavy oil viscosity compared to the diluent method in terms of cost and flow performance in pipelines.
Wettability & coalescence modulation of water droplets through surface engineering, surfactants and electrowetting
(2022-04-11) Lokanathan, Manojkumar; Bahadur, Vaibhav; Bogard, David; Mohanty, Kishore; Wang, Yaguo; Hajimirza, Shima
Fluidic separation of two or more immiscible fluids is a key process in several applications. While oil-water separation has been extensively studied, there remain significant avenues for further improvement in the effectiveness, energy consumption and speed of separation. This dissertation includes multiple fundamental studies on the influence of surface engineering (texture and chemistry), surfactants and electric fields towards enhancing separation by controlling wettability of droplets and droplet coalescence. The first task (Chapter 3) details a study of wettability of water (in oil) and oil (in water) on sub-millimeter/micro/nano textured surfaces fabricated on a variety of substrates (metals, polymers, elastomers). Importantly, all the fabrication processes employed involved non-cleanroom-based scalable techniques. Textured metal surfaces coated with Teflon AF were superhydrophobic (in oil) with very low roll-off angles (4°–7°). Uncoated textured metal surfaces were superoleophobic (in water) with roll-off angles of 3°–9°. Secondly, textured polymer and elastomer surfaces exhibited ultrahydrophobicity (in oil); however not all textured elastomers exhibited superoleophobicity (in water). Thirdly, droplet roll-off was not observed on any textured elastomer and polymer surface, despite very favorable contact angles, indicating that high contact angles do not always translate to superhydrophobicity/oleophobicity. Chapter 4 analyzes and quantifies the extent of wettability alteration of water droplets on a hydrophobic surface (in air) via the use of surfactants and electrowetting (EW). Nine surfactants were chosen from the categories of anionic, cationic and zwitterionic surfactants. EW further enhanced wettability of surfactant solutions, and further reduced the contact angle (CA) by as much as 35°. Interestingly, it was seen that the influence of EW in enabling CA reduction was reduced by the addition of surfactants at pre-CMC (critical micelle concentration) levels. Conversely, surfactants strengthened the influence of EW at higher concentrations. Finally, it was seen that at post CMC concentrations, the saturation contact angles were independent of surfactant concentrations. Chapter 5 analyses dielectrophoretic (DEP) control of a water droplet at the interface of two other immiscible liquids. An analytical model was developed which balances gravity, buoyancy, capillary, and dielectrophoretic forces to predict the change in the position of the droplet and the immersion angle. Experiments and analysis were conducted for Bond numbers ranging from 0.1 to 1.7, the latter being the critical size at which a droplet will ‘sink’ due to its weight. The predicted immersion angles and threshold voltage showed a good match with the measurements. Chapter 6 studies the influence of surfactant concentration, applied voltage, frequency and electrode geometry (spacing) on surface electrocoalescence for micron-scale water droplets in hydrocarbon media. Phase maps were developed for various electrocoalescence possibilities to identify the parameter space for significant coalescence using three dimensionless parameters: i) modified electric capillary number (Ca [superscript asterisk over subscript e], ii) frequency (τ), and iii) surfactant concentration (C*). Electrocoalescence effectiveness was quantified using the parameter (δ/α): δ is the droplet density/area and α is the fraction of surface not covered by droplets. Strong coalescence (no surfactant) corresponded to δ/α < 10 droplets/mm², with best-case δ/α = 1.6 droplets/mm², with no droplets < 20 µm diameter and electrocoalesced droplets as large as 750 µm. With surfactant, electrocoalescence weakened; parameter space for strong electrocoalescence progressively reduced with concentration. Nonetheless, electrocoalescence at all concentrations resulted in substantial radius enhancement (after/before electrocoalescence); measured ratio ranged from 3.1-6.3 in the parameter space of Ca [superscript asterisk over subscript e]: 3.3-4.9, and τ ≤ 1.25 ∗ 10⁻². This study also characterized droplet generation (via satellite droplet ejection (SDE)) of 2-10 µm radii droplets. SDE was seen to scale with voltage, frequency and concentration, and inversely with electrode spacing. Overall, it was shown that water droplets can be coalesced or generated using the same microfluidic device; the parametric space to enable fluidic separation and droplet generation was identified. Chapter 7 models the microfluidic system discussed in Chapter 6 using machine learning (ML) algorithms, such as artificial neural network (ANN), eXtreme gradient boosting (XGBOOST) and polynomial regression. Features such as voltage, frequency, electrode spacing, concentration and initial droplet density normalized with uncovered area ratio (δᵢ/αᵢ), were utilized to predict nine targets: uncovered area ratio (α [subscript f]), final droplet density normalized with uncovered area (δ [subscript f]/α [subscript f]), and seven droplet density distribution (radius) bins ranging up to 500 µm. The ANN was the most accurate and consistent among the three ML models with R² of 0.89. The model accurately predicted the droplet distribution bins for three distinct test cases consisting of good coalescence, poor coalescence and satellite droplet ejection (droplet generation). SHAP (Shapley Additive exPlanations) dependence plots highlighted the parametric influence of the features for each output. Overall, this dissertation has led to significant contributions in the field of droplet coalescence and generation. This multidisciplinary work has involved experiments, analytical modeling, numerical simulations and statistical modeling. The results show that surface engineering, surfactants and EW, in conjunction, offer powerful approaches to enhance droplet wettability and coalescence. This research impacts applications in energy (oil-water separation, enhanced oil recovery), pharmaceutical (droplet emulsion generation) and infrastructure (municipal and industrial water treatment, oil spills) areas.