Thermal destabilisation of bitumen-in-water emulsions - A spinning drop tensiometry study

Nonionic surfactant-stabilised oil-in-water emulsions offer a potentially useful vehicle for transporting heavy crude oils from oilfields to refineries or distribution terminals. Prior to refining, separation of the oil from the emulsion is necessary. Previous studies have suggested that heating the emulsion is sufficient for destabilisation and recovery of the oil. The present work examines this process on a batch laboratory scale and monitors the effect of thermal treatment on the heavy oil/water interfacial tension using spinning drop tensiometry. The present research has confirmed that heating Wolf Lake (Canada) bitumen-in-water emulsions to a temperature close to the cloud point of the surfactant results in efficient bitumen/water resolution, together with separation of a dense surfactant-rich coacervate phase that could recycled in a commercial heavy oil transportation process. The corresponding temperature dependence of the bitumen/water interfacial tension provides further insight into the emulsion resolution process.     

Influence of water-soluble and water-insoluble natural surface active components on the stability of water-in-toluene-diluted bitumen emulsion

Bitumen, a very heavy crude oil, contains both water-soluble and water-insoluble natural surface active species. This study shows that complete removal of the water-soluble surface active species from bitumen by water extraction resulted in an increased emulsion stability and that the water-insoluble surface active asphaltenes are the key stabilizing agents for water-in-toluene-diluted bitumen emulsions. Separation of the toluene-diluted bitumen continuous phase from the emulsion by centrifuging at 1, 10, 100, 1000 and 10,000g was conducted. Emulsion stability tests for the separated toluene-diluted bitumen and element analysis of the precipitated asphaltenes indicated that the asphaltenes in the separated organic continuous phase are different from those associated with the water droplet interface. The asphaltenes associated with the interface had a lower H/C ratio and a higher O/C ratio.     

Pipeline flow behaviour of heavy crude oil emulsions

Pipeline transportation of heavy oils as oil-in-water emulsions has been proposed as an alternative to blending the crude oil with natural gas condensate or other diluent. An 18 m long, 0.02 m I.D. closed loop was constructed to investigate the behaviour of an emulsified Cold Lake crude oil under pipeline flow. Pressure drop was measured as a function of flow rate for freshly produced emulsions to establish correlations of friction factor versus Reynolds number. Stability was observed for long term pipeline flow. The time at which the emulsion breakdown occurred was found to be a function of oil concentration and shear rate. The breakdown of the emulsion was clearly indicated by a simultaneous change in the system variables of pressure drop, temperature and power required to turn the pump at constant speed.     

Breakup of non-newtonian emulsion jets

The breakup of non-Newtonian emulsion jets into drops was experimentally studied by ejecting both O/W and W/O emulsions vertically downward into stagnant air through nozzles. Breakup lengths of non-Newtonian emulsion jets were found to be almost equivalent to those of Newtonian jets. Experimental breakup data establish that the static surface tension of the oil phase can be used as the surface tension of W/O emulsion jets, whereas the dynamic surface tension of aqueous surfactant solutions is used as that of O/W emulsion jets. Diameters of drops formed from non-Newtonian emulsion jets are in good agreement with the prediction from the stability theory previously developed by the authors. When the rheological index in a power law model is appreciably smaller than unity and the Ohnesorge number is significantly large, however, drop sizes are larger than the prediction because of the profile relaxation in jets. The critical velocity of emulsion jets, either O/W or W/O emulsion, is significantly lower than that of homogeneous Newtonian jets.     

聚合物3530S对坨一原油各组分油水界面性质及乳状液稳定性影响

用界面张力仪、表面粘弹性仪和Zeta电位仪研究了聚合物3530S对胜利坨一原油各组分模型油与模拟水间的界面特性及乳状液稳定性的影响规律。结果表明,沥青质及胶质模型油与模拟水间的界面张力低于蜡组分模型油,原油中的界面活性组分主要为沥青质和胶质。聚合物加入模拟水后,含有聚合物的模拟水与沥青质、胶质及蜡组分模型油之间的界面剪切粘度与界面张力均上升,油滴表面的Zeta电位降低。沥青质和胶质模型油与含聚合物3530S的模拟水所形成的W/O乳状液较蜡组分模型油所形成的W/O乳状液更稳定。     

Factors affecting the aeration of small bitumen droplets

Small bitumen droplets, roughly 10 to 40 μm in diameter, constitute a significant fraction of the total hydrocarbon in an oil sands flotation process. In this study, the aeration of such droplets is examined—both from a surface energetic perspective as well as from direct observations. The spreading coefficient associated with bitumen aeration is evaluated based on in situ measurements of interracial and surface tensions. In addition, micropipette techniques are employed to monitor the aeration process and to quantify the probability of aeration. Our results suggest that a positive spreading coefficient does not always guarantee the aeration of bitumen droplets, and that such a process may best be described from a statistical stand point.     

Study of Interfacial Interactions between Bitumen and Various Aggregates Used in Road Construction

Our objectives were first to develop new physico-chemical methods to characterise the aggregate, the bitumen, and the bitumen emulsion surfaces, then to compare the properties of the new sustainable emulsifiers with those currently used in the road industry, and finally to explain the role of the bitumen/aggregate interactions in the bitumen emulsion breakdown. It was possible by using a Drop Shape Analysis System to determine the surface tension of complex liquids such as bitumen, surfactant containing aqueous phase, and bitumen emulsions. The interfacial phenomena between a bitumen emulsion and an aggregate are driven by the polar and dispersion interactions. The polar interactions play a major role in the emulsion adhesion to the aggregate and also in the emulsion breakdown.     

A filtration model for the flow of dilute,stable emulsions in porous media—I. Theory

Flow of dilute, stable emulsions in porous media is important in several oil recovery processes. Because underground media have relatively low permeabilities, the emulsion drop sizes may overlap the pore sizes. Hence, strong interaction occurs between the emulsion droplets and pore constrictions, and local flow redistribution occurs within the porous medium. To predict quantitatively how emulsions are transported in underground media, a theoretical model is required which correctly accounts for the interactions between the flowing droplets and the pore walls.In Part I of this work, we present a simplified filtration model describing the flow of stable, dilute emulsions in unconsolidated porous media. In the model, emulsion drops are captured in pores by straining and interception and, thus, reduce the overall permeability. Transient flow behaviour is characterized by there parameters: a filter coefficient, a flow-redistribution parameter and a flow-restriction parameter. The filter coefficient controls the sharpness of the emulsion front, the flow-redistribution parameter dictates the steady-state retention, as well as the flow redistribution phenomenon, and the flow-restriction parameters describes the effectiveness of retained drops in reducing permeability.Critical comparison is made between the new filtration theory and the current continuum—viscous and retardation models for emulsion flow in porous media. Only the filtration picture is able to explain all the experimental observations. Quantitative comparison between the filtration flow theory and experiment is presented in Part II.     

Monte Carlo Simulation of Coalescence Processes in Oil Sands Slurries

Conditioning of an oil sand slurry is a critical step in the extraction of bitumen from oil sand ore. To model the conditioning process, a constant‐number Monte Carlo algorithm is used to simulate the mean‐field kinetics of coalescing bitumen drops and air bubbles. The coalescence rate of drops and bubbles is described by the model of Coulaloglou and Tavlarides (1977). Simulations yield results that are consistent with aerated bitumen drop sizes and conditioning times reported in the literature. The effects of turbulent energy, bitumen concentration, and initial bitumen drop size on the evolution of drop size distributions are investigated.     

Adsorption of surfactant during chemical enhanced oil recovery

Surfactant is extensively used as chemicals during chemical enhanced oil recovery (CEOR) process. Effectiveness of surfactant CEOR process depends on several parameters like formation of micro emulsion, ultra-low interfacial tension (IFT) and adsorption of surfactant. First two parameters enhance the effectiveness while the last parameter reduces the effectiveness. Micro emulsions are highly desirable for CEOR due to its low interfacial tension (IFT) value and higher viscosity. In this research the size of the emulsions were studied with particle size analyzer to study the liquid–liquid absorption process and the entrapment of oil drops inside surfactant drop. Initially, the average surfactant drop size was found to be 100 nm, after mixing the surfactant slug with reservoir crude, the size was increase up to 10 times. It signifies the formation of micro emulsion between surfactant and oil. Another attempt was done in this research to study the adsorption mechanism of surfactant on reservoir rock. The process of adsorption was studied by Langmuir and Freundlich isotherm to understand the adsorption phenomena. In this study, it was found that the adsorption follows Freundlich isotherm and the adsorption phenomena was chemical for surfactant flooding process. In chemical adsorption phenomena, the rate of adsorption is high because, surfactant molecules are adsorbed layer after layer by the rock surface. Use of alkali along with surfactant reduces adsorption of surfactant since, alkali blocked the active clay sites before interacting with surfactant and hence the adsorption isotherm was found to be Langmuir and phenomena was physical adsorption.     

Formation of O/W emulsions by static mixers for pharmaceutical applications

Oil-in-water (O/W) emulsions produced by static mixers in the laminar flow regime are characterized for their oil drop size spectra. The emulsions are used in the first process step for the production of microspheres for pharmaceutical applications by the emulsion extraction method. However, emulsion generation by static mixers in the laminar flow regime is rarely discussed in the scientific literature. Here we deduce a non-dimensional correlation for predicting the Sauter mean oil drop size as a function of the static mixer operation parameters and the liquid properties. First, the material properties of the organic and water phases are characterized. Second, the oil drop size spectra of the emulsions are measured by laser diffraction. Dimensional analysis is used to describe the relationship between the process parameters of the static mixer and the Sauter mean oil droplet size. Emulsion production experiments using SMX static mixers with two different diameters are carried out with the mixing of the two liquids taking place in the laminar flow regime. We provide results covering a wide range of all process parameters, which were identified influencing the droplet size of the emulsion. The correlation achieved is related to the non-dimensional drop-size based Ohnesorge number of the emulsification process and allows for the prediction of the mean oil droplet size with good accuracy, which is an essential information about the emulsion properties relevant for the pharmaceutical application.     

石油磺酸盐对原油界面性质及其乳状液稳定性的影响

The influence of petroleum sulphonate （TRS） on interfacial properties and stability of the emulsions formed by formation water and asphaltene, resin and crude model oils from Gudong crude oil was investigated by measurement of interfacial shear viscosity, interfacial tension （IFT） and emulsion stability. With increasing petroleum sulphonate concentration, IFT between the formation water and the asphaltene, resin and crude model oils decreases significantly. The interfacial shear viscosity and emulsion stability of asphaltene and crude model oil system increase for the petroleum sulphonate concentration in the range 0.1% to 0.3%, and decrease slightly when the concentration of the surfactant is 0.5%. There exists a close correlation between the interfacial shear viscosity and the stability of the emulsions formed by asphaltene or crude model oils and petroleum sulphonate solution. The stability of the emulsions is determined by the strength of the interfacial film formed of petroleum sulphonate molecules and the natural interfacial active components in the asphaltene fraction and the crude oil. The asphaltene in the crude oil plays a major role in determining the interfacial properties and the stability of the emulsions.     

Aging Effects on Surface Properties and Coalescence of Bitumen Droplets

The coalescence of emulsified bitumen droplets is examined, from the perspective of material surface properties, at temperatures of 22°C and 40°C over exposure periods of up to 8 h. The study was undertaken to better understand the nature of oil sands ore conditioning in the water‐based bitumen extraction processes of Syncrude Canada Ltd. Measurements of the bitumen droplet electrophoretic mobility showed only a slight degree of variation with temperature. The mechanical stress‐strain behaviour of the droplets was investigated using a micropipette‐based technique. These results indicate that the interfacial dilational elasticity of bitumen droplets depends on temperature and droplet age, while the tension is relatively invariant to duration of exposure. Interaction experiments between emulsified bitumen droplets quantify a coalescence probability that correlates with dilational elasticity at their surfaces.     

Calorimetric investigation of cyclopentane hydrate formation in an emulsion

Differential scanning calorimetry (DSC) is applied to investigate the formation of cyclopentane hydrates in a water-in-oil emulsion. Protocols of cooling below the ice formation temperature and warming to a temperature above the ice and hydrate melting temperatures are applied. Cyclopentane, which forms hydrates at atmospheric pressure, is a component of the continuous oil phase in the hydrate-forming emulsion and is replaced by iso-octane to obtain a comparable ice-forming emulsion. A method based on comparing the heat flow measured by DSC for samples of identically prepared hydrate-forming and non-hydrate (ice-forming) emulsions is developed to obtain the rate of cyclopentane hydrate growth. Results are reported for a 40% water volume fraction emulsion. Experimental results lead to the conclusion that the hydrate formation takes place primarily at the interface between water drops and the continuous oil phase. In the absence of surfactants, a robust hydrate “shell” develops around the water drop limiting transport of hydrate former to the free water which remains trapped inside the hydrate layer. Direct visualization of hydrate formation in larger water drops under the influence of oil-soluble surfactants shows that the hydrate crystals have much smaller features and the appearance is hairy or mushy. A three-step mechanism – nucleation, surface growth and radial growth – is described to capture the main features of the hydrate formation process. Mechanical stresses developed in the hydrate shell due to volume expansion upon hydrate formation (a liquid–solid transition) are analyzed.     

Stabilisation of emulsion droplets by fine powders

Finely divided solids can stabilize emulsion droplets provided the solids are partially wetted by both the disperse liquid phase and the continuous liquid phase. The stabilisation of oil/water emulsions by finely divided solids in the presence of suitable organics has been related to the three phase (solid/oil/water) contact line. Schulman and Leja (1954a) and Taubman and Koretskii (1965) provide evidence that O/W emulsions are formed when the contact angle is less than 90° but inversion occurs to W/O emulsions when the contact angle exceeds 90°. We present a thermodynamic study of emulsion stabilization by finely divided solids, which is an extension of an earlier theory by Van der Minne (1928) who neglected interactions among the particles and droplets and also entropy effects due to Brownian motion. Only stable W/O emulsions are considered here. The starting point of the theory is an expression for the Helmholtz free energy associated with the oil/water interfaces stabilized by finely divided solids in the presence of surfactants. By minimising this free energy, it is shown that in a stable emulsion almost all the solid particles are adsorbed at the oil/water interface of the oil drops. This accounts for the experimental result that the average size of oil droplets decreases with increase in the concentration of solids. A particular example of emulsion stabilization by solids occurs in the hot water extraction process on the Athabasca oil sands. Both clay particles and anionic surfactants act as stabilizers of the bitumen droplets suspended in an aqueous alkaline environment.     

Stability of multiple emulsions under shear stress

Multiple liquid emulsions of the water in oil in water (W₁/O/W₂) type are used in a variety of consumer or technical applications, for instance in the encapsulation of certain active ingredients. The encapsulation process and release mechanisms of the inner phase of the carrier drops are important in order to properly process and formulate such liquid-liquid systems. In this work the stability and breakage of multiple W₁/O/W₂ emulsions under mechanical shear stress are investigated for emulsions with different surfactants and surfactant concentrations of the internal emulsion. Stressing the emulsions in a mechanical stirring process is compared to the membrane emulsification process. The membrane emulsification process results in higher encapsulation efficiencies than the stirring process. The emulsion droplets were subjected to shear stress below and above the critical capillary number for drop breakup. The results show that stable inner emulsions with sufficient surfactant concentrations increase the overall encapsulation efficiency for multiple emulsions subjected to shear stress, although the effect is not prominent. The depletion of the carrier oil droplets could be achieved for Ca numbers below the critical limit, reducing the encapsulation efficiency below 10 %. This shows that even a low shear stress can result in content release from the internal droplet phase. The experimental emulsion release study is supported by a numerical simulation of drop deformation and break-up under shear stress.     

The effect of monoethylene glycol on the stability of water-in-oil emulsions

It is important from both a strategic and economic standpoint to study the mechanism of formation of water/oil emulsions, to predict their increase of viscosity with respect to that of the crude oil, and to obtain information about the stability vs separation of these substances (since their presence can impair oil processing and distribution). The objective of this work was to ascertain the influence of monoethylene glycol (MEG) on these parameters and its action mechanism. The addition of MEG in different proportions in the oil emulsions significantly changed the flow curve of the emulsion, passing from a quasi-Newtonian one to a shear thinning behaviour. Besides this, when MEG was present at low concentrations, the demulsification process was slow and an increase in concentration made the emulsions more stable than samples containing the same aqueous phase proportion. Under the conditions studied, the addition of MEG did not reduce the quantity of the aqueous phase separated compared to the emulsions free of MEG, but significantly delayed the demulsification process. Rheology provided important information regarding the phase separation process of the aqueous phase in oil phase emulsions, and dynamic testing suggested that the most relevant effect of the addition of MEG is an increase of the emulsion elasticity that can be correlated with the increase in the emulsion stability observed by bottle test and Turbiscan.     

模拟乳化体的制备和研究

随着三元复合驱采油技术的大面积推广,三元复合驱采出液的化学破乳作为重要的配套技术也开始成为人们必须关注的问题。在对三元复合驱采出液化学破乳的室内研究中,受工作时间和条件的限制,不可能以不同的采出阶段的油田的实际采出液作为研究客体进行实验。因此,本文考虑以杏1- 4-23和杏2-2-试采出液上层乳化油和下层游离水按一定比例混合后均质制得模拟乳化体。考察了影响模拟乳化体性状的因素,并与实际采出液的性质作对比。     

Interfacial Activity of Bitumen Components

The interfacial activity of asphaltenes, naphthenic acids, and naphthenates has been amply studied in the literature, as they are involved in the formation and stabilization of bitumen and heavy crude oil emulsions. While most of the literature evaluates one component at a time, in this work these bitumen components were separated one at a time from Athabasca bitumen, and the surface activity of the resulting fraction was evaluated as a function of pH, solvent aromaticity (heptane/toluene mixtures, known as heptol, at volume ratios 50/50 and 80/20), and temperature for selected systems. The interfacial activity was evaluated in two ways: via dynamic interfacial tension during adsorption on a bitumen drop of constant volume, and via dynamic interfacial tension during drop volume cycling. The adsorption data were interpreted using a model that combined multicomponent adsorption kinetics inspired by Langmuir–Freundlich kinetics with the Fainerman surface equation of state. The volume cycling experiments were interpreted using the compression relaxation model, which segregates adsorption/relaxation effects from elastic phenomena at interfaces. Overall, the adsorption data confirmed that naphthenic acids are the fastest adsorbing species that tend to dominate the interface, but that asphaltenes adsorb, almost irreversibly, at longer time scales and likely forming a sublayer previously proposed in the literature. The dilatational elasticity of the interface seems to be highly influenced by that asphaltene sublayer, which softens at high pH at room temperature, or at 80 °C independently of the pH of the system.     

油水乳状液的稳定机理及其化学破乳技术的研究进展

油/水乳状液的破乳是重油生产和加工过程的重要环节,破乳剂的研发一直是油田化学中重要的研究内容。本文综述了国内外化学破乳剂研发的现状与趋势,阐述了重油中以沥青质为主的天然乳化剂的结构特点,深入分析了沥青质在油水乳状液的形成与稳定的过程中所起到的关键性作用,揭示了油水乳状液的形成与稳定性机理。进一步论述了具有普适性强、无毒、可生物降解且价格低廉的天然高分子破乳剂的破乳作用及其最新研究结果。重点介绍了微吸液管技术和原子力显微镜技术等现代分析手段在油水乳状液破乳过程中对相关微观机理研究的重要应用。