Indigenous Surfactants Research Articles

Experimental investigation of the Electrical Submersible Pump's energy consumption under unstable and stable oil/water emulsions: A catastrophic phase inversion analysis

The presence of water in crude oil exploitation by the Electrical Submersible Pump (ESP) systems may cause several problems in energy consumption and operational instabilities due to emulsion formation. Indigenous surfactants in crude oil also contribute to emulsion stabilization, which can exacerbate these problems. In this paper will be experimentally investigated the influence of the emulsion stability on ESP energy consumption and operational instabilities through an 8-stage ESP operating with unstable and stable emulsions, with and without a demulsifier. The experimental tests were performed for one oil viscosity, a constant total flow rate, and two ESP rotational speeds. Initially, the ESP relative dimensionless power (RDP) was analyzed along with the emulsion system and the droplet size distribution (DSD). An interesting difference regarding the presence of surfactants was observed experimentally in the RDP and phase inversion points. The relationship among the ESP dimensionless power, torque, and electrical current with maximum droplet size allowed to conclude that these parameters can be related to the start of the coalescence process, i. e, able to predict the catastrophic phase inversion (CPI) point.

The effects of pH, acidity, asphaltene and resin fraction on crude oil/water interfacial tension

A basic understanding of the activities of indigenous surfactants of crude oil at the water/oil interface as a function of aqueous phase pH can give us a better insight into the alkaline enhanced oil recovery processes. The present study aimed to elucidate the effect of salinity and crude oil type, specifically the influence of resin and asphaltene molecules during alkaline flooding through interfacial tension (IFT) measurements via pendant drop and spinning techniques. Several model oils containing asphaltene and resin fractions were prepared and their IFTs were compared with those of the original crude oils. Moreover, the elemental analyses of asphaltene and resin fractions were performed, and the total acid numbers of all oils were measured as well. The IFT results of three studied crude oils and the asphaltenic and resinous model oils with sea water and deionized water underlined the importance of the degree of salinity, and qualitative and quantitative nature of resin and asphaltene fractions. It was also revealed that the amount of asphaltene and resin fractions as well as their structural nitrogen and oxygen contents were the most influential parameters on the IFT of crude oil as a function of pH values. In addition, the variations of IFT crude oils/the ionic solution and deionized water were more noticeable in the basic aqueous solutions.

Effect of Aqueous Phase pH on the Dynamic Interfacial Tension of Acidic Crude Oils and Myristic Acid in Dodecane

The time dependence of the interfacial tension between water–acidic crude oil and water–synthetic oil was investigated for aqueous phase pHs ranging from 2 to 9 using the du Noüy ring method at 20°C. Myristic acid in dodecane was selected as a model (synthetic oil) for acidic crude oil containing indigenous surfactants, and the similarities and differences between the dynamic interfacial tension behaviours of the natural and synthetic crude oil systems were compared. The initial interfacial tension and the relaxation of the interfacial tension are sensitive to the aqueous phase pH for both systems. The adsorption kinetics of the indigenous surfactants and myristic acid could be well fitted with the monoexponential model, and the time constants obtained in this manner indicates that reorganization of the indigenous surfactants and myristic acid at the w/o interface are pH dependent. The experimental results also indicate that indigenous surfactants in acidic crude oil and myristic acid in dodecane have similar film formation behaviours at the w/o interface for the range of pHs investigated.

Thixotropy in Native Petroleum Emulsions

Native water in crude oil emulsions, stabilized by indigenous surfactants, exhibit both positive thixotropy (PT) and negative thixotropy (NT) in Couette flow. PT is associated with microscopic processes, local break-up of droplet clusters in emulsions with low and moderate volume fractions of water φ, or fracturing of emulsion-gels with φ > 0.7. The latter process involves the coalescence of water droplets along a fracture plain, which results in vorticity banding of emulsion flow. NT reflects evolution of the macroscopic radial banding in flow of emulsions with 0.18 < φ < 0.58 and is dictated by the displacement of the interface between the sheared and unsheared regions.

Composite Particles of Disinfectant Nanocapsules-Skim Rubber Latex

Skim latex, a by-product of natural rubber latex, was prevulcanized by sulfur and then used in the preparation of composite particles with disinfectant nanocapsules. Each polymeric nanocapsule contained chlorhexidine digluconate (CHD) as a disinfectant agent encapsulated with poly(methyl acrylate) (PMA) as a shell. The driving force for the heterocoagulation of CHD-PMA nanocapsule and sulfur-prevulcanized skim (SPVS) particle was the electrostatic interaction between the positive charge of lecithin residing on the surface of the nanocapsule and the negative charge from the indigenous surfactant (protein-lipid) and/or from sodium dodecyl sulfate on the surface of the SPVS latex particle. The zeta potential and morphology of heterocoagulated particles indicated the formation of the CHD-PMA/SPVS composite particles. Structures and formation mechanisms of the composite particles with different blend ratios were revealed by depth profiling confocal Raman spectra.

Preparation of core-shell particle of disinfectant agent nanocapsules-skim rubber particles by the heterocoagulation technique

Sulphur-prevulcanised skim (SPVS) rubber particles were heterocoagulated on an aggregate of a disinfectant agent (chlorhexidine digluconate; CHD)-poly(methyl acrylate) (PMA) nanocapsules. The CHD-PMA nanocapsule stabilized by lecithin was prepared using the modified nanoprecipitation of PMA from an organic continuous phase onto nanodroplet containing the CHD aqueous solution. Cationic and anionic nanocapsules were produced by separately redispersing the nanocapsules into a water and 0.5% sodium dodecyl sulphate (SDS) aqueous solution, respectively. The largest aggregate, which was obtained from homocoagulation of the CHD-PMA nanocapsules with opposite charges, was selected as a core surrounded with SPVS shell particles. An interpolymer complex between poly(ethylene oxide) (PEO) moieties adsorbed on the aggregate and indigenous surfactant (protein-lipid) and/or SDS on the SPVS particle surface was the driving force for heterocoagulation. Data from the size, zeta potential measurements and TEM images of the heterocoagulated CHD-PMA/SPVS indicated the composite particle containing the CHD-PMA core.

Prevulcanisation of skim latex: morphology and its use in natural rubber based composite material

The prevulcanisation of skim latex, a by-product of field natural rubber (NR) latex concentrated by centrifugation, using sulphur and peroxide systems was investigated. Compared to the peroxide prevulcanisation, the lower swelling ratio of film casted from sulphur-prevulcanised skim (SPVS) latex was observed. The latter was then employed for preparation of NR/SPVS core–shell particles by using heterocoagulation technique whose driving force was an interpolymer complex between poly(ethylene oxide) (PEO) moieties of a non-ionic surfactant (Nonidet) adsorbed on small SPVS particles and the indigenous surfactant (protein–lipid) on a large NR particle. The value of zeta potential of heterocoagulated particle and the better oil resistance of films casted from the composite latex when compared to that of the NR film revealed the NR/SPVS core–shell structure.

Excess density in oilfield water—crude oil dispersions

Extensive density measurements were performed with mixtures of 12 degassed (dead) crude oils with respective oilfield brines (formation waters). All unprocessed samples were collected directly from wellheads and contained only indigenous surfactants, such as asphaltenes and fine solids. Nonzero excess densities and excess thermal expansions (evaluated on the assumption of quasi-binary water–oil mixtures) were observed for water cuts in the range from X = 0.4 to 0.6 at all studied temperatures T = 5 – 50 ° C . We suggest that these results are due to the formation of a dense asphaltene-mediated “middle phase” in the studied w/o dispersions. This suggestion is substantiated by plotting T– X phase diagrams which topologically strongly resemble those conventionally observed in some standard Winsor III-type systems. The formation of a complexly structured “middle phase” has been directly verified by preliminary visual/microscopic studies of a phase separation in a crude oil–water mixture.

Composite natural rubber based latex particles: a novel approach

The oil resistance of natural rubber (NR) film could be effectively improved by using the heterocoagulation of large NR particle with small polychloroprene (CR) particles. In the preparation of NR/CR composite particle with a core-shell structure, a nonionic surfactant whose molecule bears poly(ethylene oxide) (PEO) was adsorbed on CR particles and allowed to form complexes between PEO and indigenous surfactant (protein–lipid) on the NR particle surface. Composite latex particle obtained was characterised by particle size, zeta potential and glass transition temperature measurements and the data indicated the presence of CR on the outer layer of composite particle. Better oil resistance of film casted from heterocoagulated latex when compared to that of NR film confirmed the NR/CR core-shell structure. The epoxidised natural rubber (ENR), crosslinked ENR and/or skim latex particles were investigated in order to replace the use of CR in the heterocoagulation process.

Heterocoagulation of polychloroprene on natural rubber latex particles for use in the preparation of toughened polystyrene

AbstractThe toughness of high‐impact polystyrene based on γ‐radiation‐vulcanized natural rubber (NR) was effectively enhanced by the addition of a block copolymer at the NR/polystyrene interface. An NR/polychloroprene (CR) composite latex particle was produced by the heterocoagulation technique for its use as a model in a compatibilization study. A nonionic surfactant (Tween 80), whose molecule bore poly(ethylene oxide) (PEO), was adsorbed onto the CR particle and allowed to form a complex between PEO and an indigenous surfactant (protein–lipid) on the NR particle surface. The presence of CR–Tween on the outer layer of the obtained composite polymer particle was characterized by the particle size, ζ potential, and glass‐transition temperature. That the film cast from the heterocoagulated latex showed better oil resistance than the NR film confirmed the NR/CR core–shell structure. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 9–13, 2003

Composite natural rubber-polychloroprene latex particles produced by the heterocoagulation technique

Composite natural rubber (NR) based latex particles were prepared using the heterocoagulation technique. A nonionic surfactant (Tween 80) whose molecules bear poly(ethylene oxide) (PEO) was adsorbed on polychloroprene (CR) latex particles and allowed to form complexes between PEO and indigenous surfactant (protein–lipid) on the NR particle surface. The heterocoagulated NR/CR–Tween particles produced were characterised by particle size, zeta-potential and glass-transition temperature measurements and the data indicated the presence of CR–Tween on the outer layer of the composite polymer particles. The results agreed well with the better oil resistance of films cast from heterocoagulated latex when compared with that of the NR film.

Selective membrane test for crude oil based model emulsions by use of video-enhanced microscopy

A method for testing water/oil emulsion droplet membranes selectively has been demonstrated. The method uses electric fields to induce attraction, membrane thinning and coalescence between aqueous droplets deposited in an oil continuum. The coalescence process is monitored visually by the use of videomicroscopy. A set of model oils containing indigenous surfactants (asphaltenes) from a crude oil has been studied, and the effects of asphaltene concentration, oil phase aromaticity, aging of oils and interfacial exposure time have been investigated. The strength of the field at the point of coalescence is defined as the critical parameter describing membrane strength. In the current experiments a.c. fields were used and droplet sizes were of the order of 500–600 μm.

Percolation Behavior in W/O Emulsions Stabilized by Interfacially Active Fractions from Crude Oils in High External Electric Fields

In this communication we report on a percolation behavior of water in oil emulsions stabilized by indigenous surfactants from crude oils in high external electric fields. The static permittivity of the emulsion investigated increases with the applied electric field. When the electric field reaches a certain strength the system collapses and the permittivity of the system resembles that of a series coupling of the water and the oil domains. Regression analysis of a proposed scaling law shows that the system behaves according to a static percolation model, i.e., a bicontinuous system. We compare the percolation behavior in high electric fields to that reported in temperature and conductivity studies in w/o microemulsions.

Crude oil emulsions in high electric fields as studied by dielectric spectroscopy. Influence of interaction between commercial and indigenous surfactants

The behaviour of different types of water-in-oil emulsions in high electric fields as investigated by means of time-domain dielectric spectroscopy (TDS) is reported. The studied emulsions include true crude-oil-based ones as well as model systems stabilised by indigenous crude oil fractions or, alternatively, by commercial nonionic surfactants. It is seen that the developed TDS equipment gives a good quantitative measure of the emulsion stability. The emulsion stability in crude oil systems can be modelled by the separated asphaltene fraction as far as coalescence is considered. Although the resin fraction might be even more interfacially active than the asphaltenes, it cannot alone stabilise the w/o emulsions. The importance of the interplay between the asphaltenes and resins is clearly revealed. When commercial surfactants (ethoxylated nonyl phenols, NP-EO or monoalkyl sorbitan esters) are combined with the separated crude oil fractions, different levels of compatibility are displayed. The addition of a tetraoxyethylene nonyl phenol ether (NP-4), for instance, completely destabilises the original emulsion, although a high level of interfacial activity is retained in the system.

BASIC STUDY REVEALS HOW DIFFERENT CRUDE OILS INFLUENCE DISPERSANT PERFORMANCE

ABSTRACT Previous research has shown that crude oils contain various amounts of indigenous surface active agents that stabilize water-in-oil emulsions. It is also known that crude oils stabilize such emulsions to different extents. One aspect of the study was to investigate the relationship between the emulsion forming tendency of the various crude oils and the level of performance of a chemical dispersant on the particular crude oil. The results of the extensive laboratory test program indicated that dispersant effectiveness is a function of both dispersant type and the specific crude oil. However, there is no apparent correlation between the degree of emulsion-forming tendency of the crude oil, which is a function of the indigenous surfactant content, and effectiveness. A “clean” hydrocarbon, tetradecane (C14), was also tested in order to evaluate the absence of any indigenous surfactants on performance. It was found that tetradecane exhibited a higher level of effectiveness compared to the crude oils for each of the dispersants tested. In essence, the indigenous surfactants in the crude oil, in every instance, reduce dispersant effectiveness but to an unpredictable level. This is probably due to the fact that these agents present in crude oil promote a water-in-oil emulsion. Since the chemical dispersant is formulated to produce an oil-in-water dispersion, the interference of these crude oil surfactants is apparent. Hence, tetradecane would be an ideal test oil since the degree of dispersion of tetradecane by a particular dispersant represents the maximum dispersion effectiveness for that product. In order to establish more definitively the role of the indigenous surfactants, this surfactant phase was successfully separated from nine crude oils representative of different emulsion forming tendencies. It was found that the amount of surfactant residue extracted from the crude oil did correlate with the emulsion forming tendency of the crude oil. Finally, the above separated surfactant residue was added to tetradecane at the same concentrations as in the respective crude oil. As expected, in every instance, the surfactant residue decreased dispersant performance compared to “pure” tetradecane.