Onset Of Flocculation Research Articles

Assessment of Asphaltene Stability in Crude Oils Using Conventional Techniques

Fundamental physicochemical factors involved in asphaltene precipitation under ambient conditions are studied in an effort to correlate them with the precipitation behavior observed in the oilfields. Asphaltene stabilization was evaluated by flocculation onset determination in titration experiments. The reversibility of asphaltene precipitation at ambient conditions was also explored with the proposed titration technique. It was found that the flocculation onsets of recombined long distillation residua are usually lower than the ones of the original samples.This finding suggests an irreversible nature of the process; this irreversibility is particularly observed for crude oils deemed stable from their field production records. Physicochemical characterization of crude oil hydrocarbon group-types was carried out and their influence on asphaltene stability was evaluated. Stable crude oils are characterized by possessing asphaltenes with lower density and lower aromaticity, compared with asphaltenes from unstable crude oils. Their resins show a higher stabilizing activity than the ones from unstable crude oils, and their maltenes also exhibit higher asphaltene stabilization effectiveness. Flocculation onsets of stable crude oils are higher than the flocculation onsets of unstable oils, at the same asphaltene content in the sample to be titrated. On the basis of this finding, a simple method is proposed for the evaluation of the possible risk of asphaltene precipitation in the oilfields.

The influence of xanthan andlambda-carrageenan on the creaming and flocculation of an oil-in-water emulsion containing soy protein

The effect of polysaccharide content on the stability of an oil-in-water emulsion (20% oil, droplet diameter 6.5 mum, pH = 7) containing soy protein (5 mg/ml) as the emulsifying agent was studied. Flocculation occurs by addition of two depletion flocculants: xanthan (0.01- 0.4%) and lambda-carrageenan (0.001- 2%). We report that in both cases the onset of flocculation occurs below the overlap polymer concentration (c* = 0.15 % for xanthan and c* = 0.58% for lambda-carrageenan). The strength of depletion interaction is dependent on such factors as polymer concentration, molecular weight and also the presence of other macromolecules. Profiles of the creaming behaviour of the sample emulsions were obtained by measuring the height of the boundary between the cream phase and the serum as a function of time for each emulsion. The result indicates that creaming kinetics is dependent on polymer concentration in a complex way. The turbidity of the serum gave an indication of whether the system was fully flocculated or contained flocks together with unflocculated droplets. At very low polymer concentrations the droplets cream individually or in small aggregates at the top of the container. At higher concentrations the droplets appear to cream as a single entity, with a sharp lower boundary separating the cream phase from a clear serum. In these emulsions and in some of the coexistent ones, there is a delay before creaming starts. The presence of the polymers at higher concentrations resulted in a stable emulsion with a very high apparent viscosity for the continuous phase and/or a strong emulsion gel network. The length of the delay phase increased with increasing concentration of both polymers.

Single-Phase Bottomhole Sampling Technology

Abstract Oilphase, a Schlumberger company, has developed and successfully tested a novel Single-phase Sampling Technology (SST), which is in use worldwide. In this system, the collected reservoir fluid pressure is maintained at or above reservoir pressure during retrieval by the release of a pre-set nitrogen charge. Subsequent to collecting the single-phase reservoir fluid, experiments were conducted in the laboratory to demonstrate the importance of SST. Results indicate that the onset of asphaltene flocculation pressure indeed varies with the amount of asphaltene content in the reservoir fluid. The collection of a non-representative reservoir fluid sample may carry a non-representative asphaltene amount due to irreversible precipitation, and hence, result in characterization of a non-representative asphaltene flocculation onset. Therefore, asphaltene characterization on a nonrepresentative reservoir fluid sample will lead to either over- or under-design of the production system. Introduction Reservoir fluids containing hydrocarbon solids are common in the petroleum industry. The primary constituents of the solids are waxes and asphaltenes. These compounds remain in solution under reservoir temperature and pressure conditions. The hydrocarbon solids will destabilize from the reservoir fluid when the thermodynamic equilibrium conditions (that is, temperature, pressure, and composition) are altered. Asphaltenes are dark brown to black solid molecules with no definite melting point. They decompose while heating, and leave a carbonaceous residue. They are non-crystalline substances or mixtures of relatively high molecular weight fractions(1) of bitumen with characteristics of strong aromatic polar substances(2, 3). Asphaltenes are defined as the n-heptane insoluble fraction of crude oil(4, 5) that are also soluble in toluene(6). They are classified by the particular solvent used to precipitate them(7). Various laboratory techniques are used to determine the onset of asphaltene flocculation.(8–13) Most of these techniques are dependent on the oil characteristics. The most important characteristic is the colour of the oil. For dark-coloured oil, the popular light-scattering technique using a laser source in the visible spectrum becomes inadequate. In this case, near-infrared (NIR) light spectrum is necessary to identify any changes in the response due to a phase change phenomenon(14). Once flocculated, asphaltenes have the propensity to grow in size, and subsequently, may start to deposit on the reservoir and production circuit (Figure 1). Flocculation and deposition of asphaltenes have reportedly caused a multitude of operations problems(15), thereby increasing the cost of production significantly. From a reservoir management point of view, high onset of asphaltene flocculation pressure can severely limit the primary recovery potential. To avoid the reservoir pore throat clogging, operators may need to implement a reservoir pressure maintenance scheme. Recently, Kabir and Jamaluddin(16) have presented their work related to the requirements of pressure maintenance in order to produce from the South Kuwait Marrat formation without having to experience the asphaltene deposition problem. Regardless of various approaches, we believe that the correct operating procedure to minimize the asphaltene problem is not well understood. This could be attributed to our inability to retrieve a representative bottomhole sample using the conventional bottomhole sampler.

Characterization of crude oils by inverse gas chromatography

It was shown that the flocculation onset of asphaltenes in crude oils could be predicted on the basis of the inverse gas chromatography characterization of the crude oil properties. Hildebrand’s solubility parameters of four crude oils were calculated from inverse chromatography data and compared with values obtained from the onset of asphaltene flocculation measurements. A good agreement was observed with three crude oils of different origin. A relation between Hildebrand’s solubility parameter and linear solvation energy relationship descriptors was established and it was demonstrated that the solubility parameter of a crude oil is determined mainly with dispersion interactions and the hydrogen bond basicity. A large basicity lowers the oil solubility parameter, and increases its stability in respect to flocculation.

FLOCCULATION OF ASPHALTENES AT HIGH PRESSURE. II. CALCULATION OF THE ONSET OF FLOCCULATION

ABSTRACT The influence of pressure on the onset of flocculation of asphaltenes was calculated in the region from 1 to 300 bar and from 50 to 100°C. These calculations are the counterpart to our experimental data which, recently, have been reported in part 1 of an equally titled article [9]. As gas component methane and as precipitant i-octane were used. The asphaltene flocculation was considered to be a liquid–liquid equilibrium. For modelling the van der Waals equation of state (vdW-EOS) in the framework of continuous thermodynamics was applied. The composition of the crude oil was described by a continuous distribution function with respect to the solubility parameter δ of the Scatchard-Hildebrand theory. Within the distribution the asphaltenes represent the species with the highest δ-values. For oils with a very low content of asphaltenes the model developed describes the experimental flocculation data reasonably. In accordance to the experimental data the model predicts that, in the considered pressure range, without addition of i-octane asphaltene flocculation does not occur. However, on contrary to the experimental results, the model predicts the asphaltenes to show a higher flocculation tendency with increasing asphaltene content of the crude oil. For very high asphaltene contents the model even completely fails. Probably, the reason of this lack is the disregarding of asphaltene association.

Crude oil and asphaltene characterization for prediction of wetting alteration

Measures of a crude oil's polar functionality and asphaltene stability are key to predicting its wetting behavior. No publicly available data sources and few proprietary databases include all of the information necessary to characterize a crude oil with respect to its interactions with solid surfaces in the presence of an aqueous phase. At a minimum, this information includes both acid and base numbers, which are related to polar and ionic interactions between oil components and charged mineral surfaces, and refractive indeces (RI) of both the oil and oil mixtures at the onset of asphaltene flocculation, which is related to asphaltene stability. Data accumulated thus far illustrate a linear relationship between API gravity and refractive index that can be used to estimate refractive index from existing data. Acid and base numbers for many different crude oil samples show little evidence of correlation between the two, thus both numbers are needed for prediction of wetting alteration. Measurements of refractive index at the onset of precipitation with n-heptane are used to characterize asphaltene stability. Extensive data for seven crude oils are presented to illustrate how asphaltene stability can be predicted over a wide range of conditions from the n-heptane onsets.

AN EXPERIMENTAL THEORETICAL APPROACH TO THE ACTIVITY OF AMPHIPHILES AS ASPHALTENE STABILIZERS

ABSTRACT The addition of amphiphiles is one of the most frequent approaches used to prevent asphaltene precipitation in reservoir rocks and wellbore tubing. These substances can solubilize the asphaltenes otherwise insoluble under production conditions. The activity of the amphiphiles as asphaltene stabilizers is directly related to the adsorption behavior of the amphiphile on the asphaltene surface. In this study, a semiquantitative description of the adsorption behavior of different amphiphiles is carried out using molecular modeling to characterize the mutual interactions between the amphiphile, asphaltene and solvent. At the same time, flocculation onset measurements using n-heptane as a precipitating agent were carried out to evaluate the experimental activity of the different amphiphiles as asphaltene stabilizers. Two different indexes calculated using the mutual interaction energies amphiphile–asphaltene–n-heptane were used to correlate them with the experimental activity shown by the amphiphiles. The results obtained indicate that the activity of the amphiphiles as asphaltene stabilizers increases, as their adsorption on the asphaltene is more favorable. In fact, the net adsorption energies of amphiphiles on asphaltenes from n-heptane can be used as a good criterion for the selection of asphaltene precipitation inhibitors.

FLOCCULATION OF ASPHALTENES AT HIGH PRESSURE. I. EXPERIMENTAL DETERMINATION OF THE ONSET OF FLOCCULATION

The influence of pressure on the onset of flocculation of asphaltenes was investigated in the pressure range from 1 to 300 bar and at temperatures of 55, 75, and 100°C. Methane was employed as gas component, and i-octane was used as precipitant. The onset of flocculation was determined with a light intensity meter. Three crude oils of different provenance were chosen for the investigations. The crude oils were stabilized in a rotary evaporator at 50 mbar and 180°C, and a part of stabilized products were mixed with different amounts of n-octane or methylcyclohexane. The dependence of the onset of flocculation on the pressure is analogous for all products. The required volume of i-octane decreases strongly with pressure up to 100 bar. Above 100 bar the influence of the pressure diminishes. This dependence corresponds with the solubility of methane in crude oil products. The amount of light hydrocarbons determines the position of the pressure dependence of the onset of flocculation. Without the addition of i-octane, the onset of flocculation could not be ascertained. The observed kinetics of flocculation depends on the asphaltene content as well as on the pressure. The influence of dispersing agents was also examined.

A Two-Component Solubility Model of the Onset of Asphaltene Flocculation in Crude Oils

A new, two-component asphaltene solubility model (ASM) has been developed to predict the phase behavior of asphaltenes in crude oils. Previous asphaltene solubility models have relied for solution upon simplifying assumptions (e.g., nucleation of a pure asphaltene or pure solvent phase) and approximation methods for determining crude oil solubility parameters. No such simplifying assumptions or approximations are needed if a simple correlation between the solubility parameter and the refractive index of nonpolar species is used to characterize the oil. Compositional ranges over which asphaltenes are stable, metastable, or unstable to phase separation can be defined from calculations of changes in Gibbs free energy using the Flory−Huggins theory for mixtures of crude oil and known amounts of hydrocarbon solvents and precipitants. Coupled values of the asphaltene solubility parameter and molar volume represent the only adjustable parameters in the model. Predictions have been tested against an extensive set...

Changes in Asphaltene Stability during Hydrotreating

The conversion of asphaltenes in heavy oil hydroprocessing is important as the asphaltenic fraction often contains the most refractive components. In residual oil feeds, the content of asphaltenic sulfur amounts to less than 20% of the total sulfur content; in hydrotreated oil products, however, more than 60% of the sulfur content may be asphaltenic. When hydrotreating heavy oils, both the non-asphaltenic phase and the asphaltenes undergo a chemical conversion, which may lead to unstable products as well as to increased coke lay-down on the catalyst. To be able to explain the behavior of different catalysts, the asphaltene conversion and particularly the stability of asphaltenes in hydrotreated heavy oil products were investigated. The stability of the asphaltenes was characterized by a flocculation onset titration procedure. With this method, several different concentrations of oil in toluene were titrated with heptane, and the stability parameters were derived. This study shows how the product stability is affected by changes in reaction temperature. The critical solubility parameter for the solubility of asphaltenes follows the assumed chemistry of the hydrotreating processes in question. At low severity hydroprocessing, the stability of the product increases, but when the severity is increased, the asphaltene stability is reduced.

Variation of Oil-solvent Mixture Viscosity In Relation to the Onset of Asphaltene Flocculation And Deposition

Abstract High pressure experiments with three oils and propane as an asphaltene flocculant were performed. A capillary tube was used for the viscosity measurements. Viscosities of oil mixed with a gaseous solvent under miscible conditions were measured and compared with data on onset of asphaltene flocculation (OAF). For these oil-propane systems the OAF values were previously determined by a photometric method. Sharp increases in viscosity of the oil-solvent mixture, at increasing amounts of solvent (beyond the point of asphaltene flocculation), were detected. Viscosity increases caused by adding hydrocarbon solvent gases at high pressure were very significant in contrast to the expected decreasing trend in oil viscosities upon adding increasing amounts of a non-flocculating solvent with a lower viscosity. Upon asphaltene flocculation/ deposition, a minimum in mixture viscosity followed by a sharp increase was noted. This was interpreted as the onset of asphaltene deposition. The values of measured viscosity were compared with corresponding values obtained from diferent correlations. It was seen that these correlations resulted in values substantially lower than the real values, even at low solvent concentrations (lower than the OAF), confirming that the flocculation/ deposition mechanisms are much more complex than are generally perceived. Introduction The oil industry has faced the problem of asphaltene deposition for many years. Asphaltene deposition in the reservoir, well bores, well head equipment, pipelines and other downstream equipment can lead to serious problems and can increase the cost of producing oil. Asphaltene deposition increases whenever anything disrupts or destabilizes the asphaltene-resin micelles equilibrium. For example, the addition of low-molecular weight hydrocarbons-such as propane, n-pentane, petroleum naphtha or gasoline-will result in a flocculation of asphaltenes by solubilizing resins in the bulk oil phase. In this case the viscosity of the oil-solvent mixture would also heavily depend on asphaltene content. There are two different types of asphaltene deposition:Asphaltene deposition during primary recovery of oil, which is mainly due to the changes in pressure and temperature.Asphaltene deposition during miscible flooding involving rich hydrocarbon gases and carbon dioxide. For the latter, the most important problems are to determine:the viscosity of the oil-solvent mixture,the OAF (which is the minimum amount of solvent that would trigger the flocculation process, at the prevailing pressure) andthe onset of asphaltene deposition (OAD). The amount of asphaltene deposited is also of interest. In addition, presently, there is no reliable method to estimate the viscosity of oil-solvent mixtures for the purposes of calculating upwards flow within oil wells or, in the surface pipelines or, in flow through porous media; all the existing viscosity correlations are valid only when asphaltene flocculation does not occur. The objective of this paper is to fill this gap and to propose a method to determine the OAD. Determination of Onset of Asphaltene Flocculation for the Oil-Propane Systems As mentioned, accurate determination of onset of asphaltene flocculation (OAF) and onset of asphaltene deposition (OAD) are very important for the choice of methods for preventing/combating asphaltene deposition.

Flocculation of dilute titanium dioxide suspensions by graft cationic polyelectrolytes

The flocculation of a dilute titanium dioxide (TiO2) suspension using homopolymers and graft copolymers of acrylamide (AM) and diallyldimethylammonium chloride (DADMAC) was investigated. The graft copolymers produced by γ-irradiating the mixtures of polyacrylamide (PAM) and polyDADMAC gave better flocculating performance than homopolymers, reflecting the higher fractions of large particles and bigger floc size. A kinetic delay in the onset of flocculation was observed after adding the copolymers in the dose range 5–30 [mg polymer]/ [g TiO2]. Increasing dosage resulted in a longer delay period. No significant flocculation was observed when the dose was above 50 [mg polymer]/[g TiO2]. This delay was interpreted in terms of the re-conformation of polymer chains driven by charge neutralization, between the positively charged polymer branches and the negative particle surface. Depending on the dosage used, the flocculation behavior of the graft copolymer has been suggested to be equilibrium and non-equilibrium flocculation. It was also observed that re-conformation is not affected by the ion strength of the media, but a strong shear force significantly reduces the chain reconformation time.

Flocculation Onset Titration of Petroleum Asphaltenes

The abundantly used technique of flocculation onset titration (FT) of asphaltenes is investigated, and it is shown how additional information on asphaltene and oil properties in terms of solubility parameters may be derived from the data obtained. The classical ways of interpreting the results are outlined. Analysis of the effect of oil concentration on FT is shown to add information on the stability of the asphaltenes in the oil. Application to various areas of asphaltene stability related problems is shown. This includes emulsion stability by asphaltenes, change in stability by conversion, oil field deposition, segregation, and asphaltene dispersant evaluation. Recommendations are given on the performance of this type of experiment, such as on titration rates. The analyses of more than 25 different oils are reported in the present work.

Properties of Resins Extracted from Boscan Crude Oil and Their Effect on the Stability of Asphaltenes in Boscan and Hamaca Crude Oils

Experimental results confirm that resins isolated from Boscan crude oil have a stabilizing effect on asphaltenes in Hamaca crude oil and in Boscan crude oil. A simple experimental technique, referred to as the filter drop spreading method, was used to detect the onset of flocculation quite accurately for crude oil mixtures and for mixtures of crude oils plus additives.

Probing Static Structure of Colloid–Polymer Suspensions with Multiply Scattered Light

Time-dependent measurements of light propagation were conducted in aqueous dispersions of 523 nm diameter polystyrene at concentrations between 0.1 and 0.4 solids volume fraction in order to assess how particle correlation is influenced by depletion interactions arising from the addition of soluble polyethyleneoxide (PEO). In the absence of polymer, the transport scattering length can be predicted from Mie scattering theory and the Percus–Yevick (P-Y) model for static structure of a dense hard-sphere colloidal solution. Depletion forces arising from the addition of PEO of varying molecular weights influenced the spatial ordering of the dispersion and caused a further increase in the transport scattering length beyond that predicted by hard-sphere static structure factor but similar to that predicted by the mean sphere approximation (MSA) to the P-Y model described by Yeet al.(1996). Onset of flocculation occurred with increased PEO addition and correlated with PEO molecular weight. Phase separation was noted by no further change in the transport scattering length, except when flocculation was induced by the highest molecular weight PEO. The use of time-dependent measurements of light propagation in dense systems provides an alternative to small-angle light, neutron, and X-ray scattering characterization of interaction potentials in dense, multiply scattering samples and promises further fruitful investigation of colloidal particle interactions in suspensions.

EFFECT OF ENVIRONMENTAL CONDITIONS ON FLOCCULATION AND IMMOBILISATION OF BREWER'S YEAST DURING PRODUCTION OF ALCOHOL-FREE BEER

A method using immobilised yeasts has been developed and successfully applied for production of alcohol-free beer. The influence of environmental conditions present during alcohol-free beer production on the flocculation and immobilisation of the yeast Saccharomyces cerevisiae var. uvarum was investigated in the present study. In wort, the cells developed flocculation at the end of exponential growth, according to the NewFlo phenotype. In defined medium, the flocculation capacity appeared to be temporary and was lost rapidly during the stationary phase. No increase in cell wall hydrophobicity at the onset of flocculation was observed in either medium. Low growth temperatures increased flocculation capacity approximately four-fold, compared to growth at high temperatures. The optimum temperature for flocculation was at 25°C with cells grown at low or high temperature. A novel method using carboxyfluorescein-stained cells was developed to analyse the initial adhesion of cells to carrier. This method also allowed rapid analysis of the effects of immobilisation to DEAE-cellulose carrier during alcohol-free beer production process. It appeared that a high flocculation capacity stimulated adhesion to the DEAE-carrier.

NMR imaging studies of asphaltene precipitation in asphalts

Nuclear magnetic resonance (NMR) images were obtained on asphalts which were dissolved in toluene and titrated with iso-octane to the point of onset of flocculation. When iso-octane was added to the asphalt and the mixture stirred, asphaltene precipitation proceeded in a normal fashion. However, when the titrant was added slowly to minimize mixing at the iso-octane-asphalt-toluene interface, the images showed that a layer of material formed at the solvent interface which was different from the asphaltenes or the maltenes. The formation of this layer appeared to depend on asphaltene concentration and degree of aging, i.e. the greater the asphaltene content and the degree of aging, the more prominent the layer. The H C ratio of the layer was similar to the resin fraction of the asphalt. These observations suggest that NMR imaging might be used to assess asphalt compatibility in aged asphalts.

Viscometric Principles of Onsets of Colloidal Asphaltene Flocculation in Paraffinic Oils and Asphaltene Micellization in Aromatics

Summary Recently, we proposed a new technique for the determination of the onset of asphaltene flocculation.1 This new method is based on viscosity measurements of a crude oil upon titration with a precipitating solvent (e.g. n-pentane, n-heptane, etc.). The onset of asphaltene flocculation is detected by a sharp increase in the relative viscosity of the suspension in which asphaltene particle aggregation occurs. The key point in this development is the phenomenon of asphaltene flocculation induced by the addition of an n-paraffin hydrocarbon to a crude oil. The proposed method can also be applied to detect the onset of micellization of asphaltenes in aromatic solvents. In this paper, we validate the proposed new technique from a theoretical standpoint.

On‐line measurement and analysis of yeast flocculation

The ability of yeast to flocculate is important in different separation processes, especially in the beer industry. Because of the regulation purposes, there is a need for online monitoring. With the presented measuring set-up, consisting of a peristaltic pump, a photometer, and a computer, it is possible to determine the onset of flocculation as well as to follow flocculation intensity and the concentration of nonflocculated cells. It was found that for the yeast strain Saccharomyces cerevisiae ZIM 198 the decrease of nonflocculated cells (after flocculation has occurred) during the exponential growth can be described by an exponential equation for the first-order process, whereas the increase of free cells due to dispersion of the flocs during the stationary phase follows the form of the growth curve. It was also demonstrated that the absorbency profiles of yeast sedimentation can be described by the second-order equation suggested by Stradford and Keenan for the decrease of cell concentration during sedimentation. © 1997 John Wiley & Sons, Inc.

On-line measurement and analysis of yeast flocculation

The ability of yeast to flocculate is important in different separation processes, especially in the beer industry. Because of the regulation purposes, there is a need for online monitoring. With the presented measuring set-up, consisting of a peristaltic pump, a photometer, and a computer, it is possible to determine the onset of flocculation as well as to follow flocculation intensity and the concentration of nonflocculated cells. It was found that for the yeast strain Saccharomyces cerevisiae ZIM 198 the decrease of nonflocculated cells (after flocculation has occurred) during the exponential growth can be described by an exponential equation for the first-order process, whereas the increase of free cells due to dispersion of the flocs during the stationary phase follows the form of the growth curve. It was also demonstrated that the absorbency profiles of yeast sedimentation can be described by the second-order equation suggested by Stradford and Keenan for the decrease of cell concentration during sedimentation. (c) 1997 John Wiley & Sons, Inc.