Oil field emulsion

Chemical by itself can only do so much, treating equipment by itself, too is limited However, chemical and treating equipment together are the dual keys to the successful and economical resolution of oil-field emulsions. 

Time. It has been said that time will resolve anv emulsion. This is an arguable point, hut it is ptobably true for the tangeof oil field emulsions. Unfortunately, lime is a very expensive c ominoditv. It translates into lai ger vessels, more space and greater heat loss, to mention only a few drawbacks... 

In many instances it is the breaking of an emulsion (demulsification) which is of practical importance. Examples are the creaming, breaking and inversion of milk to obtain butter, and the breaking of W/O oil-field emulsions. Small amounts of water often get emulsified in lubricating oils, hydraulic oils and heat-exchange systems, and it is necessary to remove this water to prevent corrosion and other undesirable effects. 

Work on the characterization of oil-field emulsions coupled with chemical characterization of commercially available demulsifier formulations has shown that physical processes (temperature, pumping, and dispersed water size distribution) can be at least as important as the chemical effects associated with demulsifiers themselves in determining demulsifier effectiveness [468,469].In fact, there are so many variables involved in industrial demulsification that, to a large degree, demulsifier selection and performance evaluation are still conducted using simple test procedures developed for use in the plant or field. These tests, usually bottle or centrifuge tests, can be good indicators of performance trends, and are usually carried out for selected suites of commercial demulsifier formulations. 

A series of sulfotricarballylic acid derivatives of potential use for the resolution of crude oil field emulsions of the water-in-oil type and as detergents has been described by Ericks and Meincke.98 The preparation of these derivatives, salts of monoalkyl sulfotricarballylates and of dialkyl sulfotricarballylates, is illustrated by the following series of reactions. 

Figure 5. Some rheological measurement problems that may he encountered with practical oil-field emulsions. Initiallyy the O/W sample contained in the cylinders on the left may he homogeneousy containing oil droplets ( )y fine particles (—)y and large particles (o). After some tinWy the sample may become quite stratifiedy as shown at right.

Another option is to dye the continuous phase (J9, 20). Dyeing is best done under a microscope where the coloring of the continuous phase can be observed with an appropriate water- or oil-soluble dye. Several water-soluble dyes, such as methylene orange or methylene blue, can be used. A common oil-soluble dye is fuchsin. If methylene blue is mixed with the emulsion and no color change is observed, then the emulsion is most likely water-in-oil. The opaque nature of oil-field emulsions limits the applicability of these color techniques. 

Size Distribution Using Electrical Properties. As mentioned earlier, for water content determinations, techniques that depend upon differences in electrical properties do not distinguish between water and solids. This property limits their applicability to systems in which solids are negligible or the process stream is so well defined that the differences in signal can be attributed to differences in size distribution and not to total water and solids (50, 51). Clearly these measurements require extensive calibration and are not generally applicable to oil-field emulsions. 

To select and use the emulsion characterization technique best suited to the application at hand, it is necessary to develop an understanding of the unique capabilities and limitations of each method. Oil-field emulsion characterization requirements are generally fairly straightforward. Operations, production, and research personnel are generally interested in deter-... 

So far we have looked at the flow of emulsions in porous media in this section we discuss some aspects of in situ emulsification in porous media that have received little attention. Some evidence suggests strongly that emulsions can be produced in the reservoir rock itself. A discussion on the formation of oil-field emulsions was given by Berkman and Egloff (50). They concluded that emulsions could be formed within the porous rock near the well bore where the velocity gradients (i.e., shear rates) were very high. Emulsions could also be formed as a result of mechanical agitation, for... 

Coskuner, G. Oil Field Emulsions Report No. 1988-18 Petroleum Recovery Institute Calgary, Alberta, Canada, 1988. 

Within oil-field emulsion breaking, the economics usually favor minimal heat input because light ends are not lost to the gas phase and fuel-gas consumption is minimized. Other significant effects caused by the addition of heat are an increased tendency toward scale deposition on fire tubes, an increased potential for corrosion in treating vessels, and a tendency to render asphaltenes insoluble (because of loss of light aromatic components), which may produce an interface pad problem. 

This chapter will briefly review the nature and the consequential sources of oil-field emulsions encountered in the handling of produced fluids recovered at a wellhead and subsequently processed (Le., ""broken ) at central treatment facilities. The principal factors and agents commonly employed in the separation of both the oil and the water phases found in these produced-fluid streams will be discussed. Subsequently, this chapter will describe sampling and testing techniques that assist in characterizing a process stream s composition and thus in evaluating the effectiveness of a particular separation process. Finally, the major components of a typical oil-field emulsion-treatment facility will be described. Selection and design criteria of appropriate separation equipment will also be presented. 

As the surfactant slug is injected into the reservoir, the mixing of injected slug with reservoir components takes place. The mixing of surfactant with reservoir oil and brine often produces emulsions. Moreover, the reservoir parameters such as porosity, pressure, temperature, composition of connate water and crude oil as well as gas-oil ratio affect the formation of oil field emulsions. 

Specific ion effects are important because formation water that can be associated with oil field emulsions may vary greatly with respect to salt content. The most pronounced effects observed, particularly with North Sea crudes, is the condensing effect of Ca on the interfacial film rendering these more incompressible, resulting in more stable emulsions (1). 

Another important parameter in characterizing demulsifier performance is the range of effective concentrations. Usually a demulsifier with poorer performance but a wider range of effective concentrations is better in the field. This is because variations in the water cut in oil field emulsions can result in significant swings in demulsifier concentration on an oil basis and, without a demulsifier that performs well over a range... 

Conditioning of oil-field crude oils for pipeline quality is complicated by water produced with the oil. Separating water out of produced oil is performed by various schemes with various degrees of success. The problem of removing emulsified water has grown more widespread and oftentimes more difficult as production schemes lift more water with oil from water-drive formations, water-flooded zones, and wells stimulated by thermal and chemical recovery techniques. This chapter describes oil-field emulsions and their characteristics, treating oil-field emulsions so as to obtain pipeline quality oil, and equipment used in conditioning oil-field emulsions. 

An emulsion is a stable mixture of oil and water that does not separate by gravity alone. In the case of a crude oil or regular emulsion, it is a dispersion of water droplets in oil. Oil is the continuous phase and water is the dispersed phase. Normal, or regular, oil-field emulsions consist of an oil continuous or external phase and a water dispersed or internal phase. In some cases, where there are high water cuts, such as when a water-drive field has almost "watered out," it is possible to form reverse emulsions with water as the continuous phase and oil droplets as the internal phase. Complex or "mixed" emulsions have been reported in low-gravity, viscous crude oil. These mixed emulsions contain a water external phase and have an internal water phase mixed in the oil dispersed phase. A stable or "tight" emulsion occurs when the water droplets will not settle out of the oil phase due to their small size and smface tension. Stable emulsions always require some form of treatment. The vast majority of oil treating systems deal with normal emulsions, which is the focus of this chapter. 

Electroultrafiltration has been demonstrated on clay suspensions, electrophoretic paints, protein solutions, oil—water emulsions, and a variety of other materials. Flux improvement is proportional to the appHed electric field E up to some field strength E where particle movement away from the membrane is equal to the Hquid flow toward the membrane. There is no gel-polarization layer and (in theory) flux equals the theoretical permeate flux. It... 

Emulsifiers are used in many technical applications. Emulsions of the oil-in-water and the water-in-oil type are produced on a large scale in the cosmetic industry. Other fields of employment are polymerization of monomers in emulsions and emulsification of oily and aqueous solutions in lubricants and cutting oils. In enhanced oil recovery dispersing of crude oil to emulsions or even microemulsions is the decisive step. 

In the production of crude oil, the greatest part of the crude oil occurs as a water-in-oil emulsion. The composition of the continuous phase depends on the water/oil ratio, the natural emulsifier systems contained in the oil, and the origin of the emulsion. The natural emulsifiers contained in crude oils have a complex chemical structure, so that, to overcome their effect, petroleum-emulsion demulsifiers must be selectively developed. As new oil fields are developed, and as the production conditions change at older fields, there is a constant need for demulsifiers that lead to a rapid separation into water and oil, as well as minimal-residual water and salt mixtures. 

The separated saltwater still contains certain amounts of residual oil, where now preferentially oil-in-water emulsions are formed. The separation of the residual oil is necessary in oil field water purification and treatment for ecologic and technical reasons, because the water is used for secondary production by waterflooding, and residual oil volumes in the water would increase the injection pressure. 

The trial-and-error method of choosing an optimal demulsifier from a wide variety of demulsifiers to effectively treat a given oil field water-in-oil emulsion is time-consuming. However, there are methods to correlate and predict the performance of demulsifiers. 

G. J. W. Goudappel, J. P. M. van Duyn-hoven, M. M. W. Mooren 2001, (Measurement of oil droplet size distributions in food oil/water emulsions by time domain pulsed field gradient NMR), /. Colloid Interface Sci. 239, 535. 

Oilfield drilling fluids, organic titanium compounds in, 25 133 Oilfield emulsions, colloid, 7 274t Oilfield hydraulic fracturing fluids, organic titanium compounds in, 25 133 Oil fields, lithium in, 15 124 Oil-field waters, lithium-bearing, 15 128 Oil filters, phenolic resins in, 18 790 Oil-furnace blacks, 4 762 manufacture, 4 780—785 Oil gas, 6 787... 

Henry et al (23) have collected experimental data on cross-flow electro-filtration of Kaolin clay suspensions and oil-water emulsions. Since both the Kaolin particles and the oil droplets are negatively charged in aqueous suspensions, a direct electric field will always give higher filtration rates than cross-flow filtration alone. The level of improvement depends on the intensity of the fluid shear and the electric-field strength. Figures 47 and 48 present data for the Increase in flux with electric field strength for the oil-water emulsion and the clay suspension. 

American Institute of Chemical Engineers Journal Figure 41. Increase in flux with electric field strength on oil-water emulsion (22)... 

Although most emulsions found in the oil field are the regular or water-in-oil type, occasionally the reverse or oil-in-water type will form. At times both types may be present in the same system. Conditions necessary for the formation of a reverse emulsion include (a) large percentage of water, (b) low salt content In water, and (c) emulsifying agent present in water phase. 

While it is true that a relatively few compounds will actually treat almost all of the emulsions encountered in the oil fields, it takes many more to do a good job on the large variety of emulsions which are produced... 

In membrane distillation, two liquids (usually two aqueous solutions) held at different temperatures are mechanically separated by a hydrophobic membrane. Vapors are transported via the membrane from the hot solution to the cold one. The most important (potential) applications of membrane distillation are in water desalination and water decontamination (77-79). Other possible fields of application include recovery of alcohols (e.g., ethanol, 2,3-butanediol) from fermentation broths (80), concentration of oil-water emulsions (81), and removal of water from azeotropic mixtures (82). Membrane (pervaporation) units can also be coupled with conventional distillation columns, for instance, in esterifications or in production of olefins, to split the azeotrope (83,84). 

Free water is that water which will freely separate from oil in accordance with Eq. (4.1). Time, chemical emulsion breakers, electronic fields, and temperature are the factors that will break an oil-water emulsion. It is prudent to heat the emulsion prior to entering the electrostatic section. Such heating lowers the viscosity, which not only allows more free water removal, but also will enhance the efficiency of the electrostatic-treater section. Hereby, even a 0.5% water cut in treated oil is easily and commonly achieved. 

The water knockout tank is designed to separate all free water from the incoming field production oil. It generally uses a 30- to 60-min storage time. In many field cases, the free water is only 30 to 60% of the total water content in the oil. This is due to oil-water emulsions. The oil fed to the downstream dehydration tank (see Fig. 4.15) is treated with an emulsion breaker chemical that is injected into the feed line to the dehydrator tank. As much as 70% of the production may therefore be separated in the downstream dehydrator tank. The KO tank may also receive fresh water for desalting the crude oil through its feed line. 

In emulsion treatment, resolution refers to emulsion breaking and the separation of the oleic and aqueous phases. Example the breaking and separation of oil-field produced W/O emulsions. 

Another example of using ultrafiltration for wastewater treatment and resource recovery is the separation of oil-water emulsions generated from metal machining, oil field wastes, and enhanced oil recovery effluents. Hydrophilic membranes such as cellulose acetate are preferred because they are effective barriers to oil droplets and are less prone to fouling. The UF permeate readily meets direct discharge standards. The oil-rich stream can be processed to reclaim the oil, or disposed at reduced transportation cost because of its reduced volume. 

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