Colloidal Gas Aphrons: A Novel Approach to Preventing Formation Impairment

Colloidal gas aphrons (CGAs) were first reported by Sebba (1971) as micro bubbles (25-125 μm), composed of a gas nucleus surrounded by a thin surfactant film and created by intense stirring of a surfactant solution. Since then, these colloidal dispersions have been used for diverse applications, with a particular focus on separation processes. However, exploitation of CGAs in petroleum industry is only at the outset. CGAs were first used in west Texas in 1998, under the name Aphron drilling fluids. This kind of fluid is characterized as having a continuous phase, a high viscosity at a low shear rate and containing, as an internal phase, micro air or gas bubbles, non-coalescing and recirculating. In this paper, we illuminate the physical and chemical properties of aphron drilling fluid and its processing mechanism.

Separation of Fine Particles by Using Colloidal Gas Aphrons

This paper presents a method of separation of fine particles, of the order of a few microns or less, from aqueous media by flotation using colloidal gas aphrons (CGAs) generated in aqueous solutions. More than 150 experiments were conducted to study the effects of surfactant type, surfactant concentration, CGAs flow rate, and particle concentration on the removal efficiency (fine particles of polystyrene were used as a target compound). The results indicate that CGAs, generated from cationic surfactant of hexdecyltrimethyl ammonicum bromide (HTAB) and anionic surfactant of sodium dodecylbenzne sulfonate (SDBS), are an effective method for the separation off ine particles of polystyrene from wastewater. The flotation yields are higher than 97%.

Kinetic Rate Constant of Liquid Drainage from Colloidal Gas Aphrons

A kinetic model fitted by the empirical equation has been proposed to describe the liquid drainage behavior. Rate constants （kd） of liquid drainage equation could be obtained from the above empirical equation. In this paper, the stability of the colloidal gas aphrons （CGAs）, the effect of concentrations of sodium dodecyl benzene sulphate （SDBS）, dodecyl trimethylammonium bromide （HTAB） and polyoxyethylene sorbitol anhydride monolaurate（Tween-20）, temperature, stirring speed, stirring time, and various kinds of salts on the kd of liquid drainage are further investigated. The results show that the Arrhenius equation can be successfully used to describe the relation between kd arid absolute temperature （T）, and concentrations of surfactants, stirring speed, stirring time and salinities also have great effect on the kd. At last, the CGAs drainage mechanism is explained from analysis of the rate of liquid drainage as a function of time.

Insight into selection of appropriate formulation for colloidal gas aphron(CGA)-based drilling fluids

Application of light-weight drilling fluids is essential to develop depleted hydrocarbon reservoirs.Recently,colloidal gas aphron(CGA)-based fluids have been introduced for such applications due to their ability in controlling fluid losses.In this work,a comprehensive experimental study was performed to choose the best formulation for CGA fluids by implementing static stability tests,rheological behavior measurements,and bubble size analyses of CGAs.Xanthan gum polymer and sodium dodecyl benzene sulfonate(SDBS),an anionic surfactant,and cetyl trimethyl ammonium bromide(CTAB),a cationic surfactant,were utilized to prepare CGAs.For the range of experiments conducted,the performance of CGA fluids prepared with SDBS was improved by increasing the polymer and surfactant concentrations.However,for CTAB,it was improved by an increase in the polymer concentration and a decrease in the surfactant concentration.The formation of white,long hair-like precipitates observed at high levels of CTAB caused CGA fluid to become rapidly unstable.Also,it was observed that the size of CGAs was significantly influenced by the polymer and surfactant concentrations.The most stable bubbles were formed at 6.86 g/L of polymer concentration.The results of this study provide insights into appropriate formulation for CGA-based fluids which could be potentially applicable in drilling operations.

Experimental investigation of the impact of sugarcane molasses on the properties of colloidal gas aphron(CGA)drilling fluid

Colloidal gas aphron(CGA)based fluid has become very popular in drilling in the last two decades,as it reduces formation damages significantly.In this study,sugarcane molasses(Mls)was used for the first time as a polymer in CGA-based to investigate its ability to improve the role of aphronized fluid as a drilling fluid.The results showed that increasing the concentration of Mls to 12%(v/v)in CGA-based fluid reduces the drainage rate and increases half-life to 10.6 min,resulting in enhanced stability of the aphronized fluid.Also,because of increasing Mls concentration from 1%to 12%(v/v),the yield and the initial gas hold-up decrease to 74%and 299.4 mL,respectively,indicating that the presence of Mls allows less air into the aphron system.Although the rheological properties were improved in this study,the gel strength did not change considerably.Furthermore,the results showed that by increasing the concentration of Mls,the average size of the bubbles decreases,and the particle-size distribution becomes more uniform.Finally,the API filtration test revealed that the higher the Mls concentration in the aphronized fluid,the lower the fluid loss,and at the Mls concentration of 12%(v/v),the fluid loss was estimated at 19.54 mL.A natural polysaccharide with high molecular weight,Mls can be used as a polymer in CGAbased fluid and,thus,improve its performance.

Removal of Phenol from Dilute Solutions by Predispersed Solvent Extraction

Predispersed solvent extraction (PDSE) is a new method for separating solutes from aqueous solution by solvent extraction and one which has shown promise for extraction from extremely dilute solution very efficient and very quick. The use of colloidal liquid aphrons in predispersed solvent extraction may ameliorate the problems such as emulsion formation, reduction of interfacial mass transfer and low interfacial mass transfer areas in solvent extraction process. In present paper, colloidal liquid aphrons are successfully generated using kerosene as a solvent, tributyl phosphate(TBP) as an extractant, sodium dodecyl benzene sulphate(SDBS) as surfactant in aqueous phase and Tween-80 in oil phase. Extraction of phenol from dilute solution was studied by using colloidal liquid aphrons and colloidal gas aphrons in a semi-batch extraction column. It has been found that the PDSE process is more suitable for extraction of dilute solutions. It has also been discovered that the PDSE process has a great advantage over traditional single-stage extraction process.

Separation of Organic Dyes from Water by Colloidal Gas Aphrons

Colloidal gas aphrons (CGAs) are micron sized gas bubbles produced by stirring surfactant solutions at high speed. A single CGA dispersed in water is composed of a gaseous inner core, surrounded by a double water soapy layer. CGAs have large interfacial area per unit volume and exhibit relatively high stability. These characteristics make CGAs very suitable in flotation systems. This paper studied the flotation of organic dyes from water using CGAs. The experimental results show that the flotation process may follow four mechanisms, i.e., ion coupling of the oppositely charged species of the surfactant forming the CGA and the organic dye, reactions between CGA and the organic dye, ion dye complex adsorbed on the surface of CGAs, and hydrophilic or hydrophobic characteristics of the organic dyes.

PREDISPERSED SOLVENT EXTRACTION──THE STATE-OF-THE-ART REVIEW

Predispersed solvent extraction (PDSE) is a new extraction technique in which one of the two phases (usually the oil phase) is predispersed into minute droplets. The essential part of this novel technique is the use of colloidal liquid aphrons (CLA) together with colloidal gas aphrons (CGA). The use of colloidal liquid aphrons in predispersed solvent extraction may ameliorate the problems such as emulsion formation, reduction of interfacial mass transfer etc. In this paper, PDSE process, CLA and CGA are systematically reviewed and the potential applications of CLA, CGA and PDSE for the various areas of separation as well as the latest development in this area are discussed.