THE EFFECT OF WATER QUANTITY ON THE RELATIVE VISCOSITY OF WATER-OIL EMULSIONS

ABSTRACT

The fact that the percentage of water in the structure of the water-oil emulsion, moving mainly through pipes, from the well body to oil refining plants of oil fields, varies, affects its properties. It will be necessary to control the viscosity when the liquid passes through the pipes. This, in turn, is done by knowing the influence of various properties and indicators of the dispersion system on each other.

АННОТАЦИЯ

Тот факт, что процентное содержание воды в структуре водонефтяной эмульсии, движущейся в основном по трубам, от тела скважины до установок по переработке нефти нефтяных месторождений, варьируется, влияет на ее свойства. Необходимо будет контролировать вязкость при прохождении жидкости по трубам. Это, в свою очередь, делается путем знания влияния различных свойств и показателей дисперсионной системы друг на друга.

Keywords: water-oil emulsion, viscosity, water quantity, dispersion phase, dispersion medium, concentration, diameter, temperature.

Ключевые слова: водонефтяная эмульсия, вязкость, количество воды, дисперсионная фаза, дисперсионная среда, концентрация, диаметр, температура.

Introduction

Water-oil emulsions are usually formed from oils extracted by flooding with a high-water content under the influence of shear stresses and pressure gradients during the passage of perforations, valves, constrictions and bends of pipelines. Depending on the duration of the field operation, the amount of emulsion oil obtained increases, which introduces significant complications into the technology of mechanized production, collection and preparation of commercial oil. Complications are most often associated with the formation of oil-water emulsions in the borehole, which have high viscosity values and resistance to destruction. The increased consumption of heat, electricity and chemicals, the high cost of demulsification plants, problems with salt deposition and corrosion of equipment are the cause of high production costs and a significant increase in the cost of oil [1,2,11].

Decomposing water-oil emulsions, transportation through pipes is not organized without studying their physico-chemical properties. In this case, the dispersion must necessarily take into account all the characteristics of the components that make up the system. The composition of the water-oil emulsion, in which the volume share of water, the size of water droplets, etc., affects the relative viscosity of the water-oil emulsion.

The main part

Knowledge of viscosity is necessary when designing field pipelines through which oil is pumped from wells to its preparation plant, as well as when choosing settling equipment and its operating mode. The viscosity of the oil emulsion is not an additive property, i.e. it is not equal to the sum of the viscosity of oil and water. The viscosity of crude oil (i.e. oil containing water droplets) depends on many factors: the amount of water contained in the oil; the temperature at which the emulsion is obtained; the presence of mechanical impurities (especially iron sulfide FeS) and the pH of the water. Moreover, the dispersion and water content in the emulsion continuously change during the collection of products. In addition, oil emulsions, like paraffin oils, are a non-Newtonian liquid, so their viscosity when moving through pipelines will depend on the velocity gradient. [3,4,11]:

,

that is, µE is the apparent viscosity, so μE* = ƒ (μН, μВ, Т, W, D, pH, s, dv/dr).

The water content as a dispersed phase in an oil-water emulsion can range from traces to 80-85%.

Figure 1. Dependence of the apparent viscosity of the emulsion on the water content in the oil and the mixing temperature

From the analysis of curves fig.1. it follows that an increase in the water content in the oil emulsion to a certain limit increases the apparent viscosity μE of the emulsion, and, consequently, increases the energy costs of pumping such an emulsion.

The critical concentration of φ_cr water is called the inversion point. At the inversion point, the phases reverse and the dispersed phase (water) becomes a dispersion medium, and the dispersion medium (oil) becomes a dispersed phase. That is, the emulsion changes its type from W/O to O/W type [1,5,7].

The conversion of phases of oil emulsions is of extremely great practical importance. The O/W type emulsion is transported at lower energy costs than the W/O type emulsion. Therefore, when transporting the emulsion, it is advantageous that the external phase is water, while the pipelines must be protected from corrosion. In addition, this technique is used in the process of preparing oil to better purify it from water [6,8].

The question of the effect of the dispersion of an emulsion on its viscosity is extremely complex and in the scope of this discipline it can be considered only at the simplest level and show that with the same water content φ and the same shear rate dv/dr, the viscosity depends on the fragmentation of the dispersed phase. If this is the case, then it becomes clear that there are a large number of different formulas for the dependence of viscosity on the concentration of the dispersed phase and the spread of viscosity values that they give in relation to the same dispersed system.

The only researchers theorized that the effect of water-oil emulsion relative viscosity increase in the volumetric share of the dispersive phase. It is necessary to approach this with caution. If the volume share of the dispersion phase in the water-oil emulsion exceeds 10%, the properties of the nonyuton liquid begin to deviate to the side [9,10]. Several formulas have been developed in this regard, the exact composition is suitable for water-oil emulsion. The reliability of the formulas requires the researchers to know the volumetric size of the drops, to what extent, the reduction in the size of the drops leads to an increase in the relative viscosity of the emulsion. This effect by the formula F.Sherman is written as follows:

here: - effective viscosity of the emulsion, Pa*s;

 dynamic viscosity of the dispersive environment, Pa*s;

the average diameter of the water drop in the emulsion, m;

Х and С – constants.

The value of the emulsion depends on the type and viscosity of the hydrocarbon environment and the water phase, temperature, nature and concentration of emulsifiers and solid particles, the presence of dissolved gases [2,11].

One of such bonds is the A.Einshteyn formula,  is in the proportion of water as follows:

Eyler equation when

H.C.Bringman and R.Roscoe  an  have established the following relationship for a wide range of water drop sizes in the emulsion:

and in their narrow dispersion, respectively

for high-concentration emulsions, the E.Hatchek formula is used:

Water-oil emulsion the larger the diameter of the water droplets in the composition, the lower the emulsion viscosity and vice versa (Fig.2).

Figure 2. Water-oil emulsion effective viscosity dependence on water drop diameter  

As can be seen from the graph, a decrease in the diameter of water droplets leads to an increase in the effective viscosity of the water-oil emulsion.

Data on critical water content φ_cr for oil emulsions at a temperature of 20 °C, as well as viscosity at the phase inversion point are presented in table 1. [6,8,11] The data are compared with other water content of these oils.

Table 1.

Data on critical water content φ_cr for oil emulsions in Uzbekistan at a temperature of 20 ° C, as well as viscosity at the phase inversion point

Conclusion

If it is possible to improve the processes of its preparation and transportation by reducing the viscosity of the water-oil emulsion, then in order to reduce the viscosity, it is necessary to use different methods of action to increase the dispersive phase dimensions, that is, to merge the water droplets. Therefore, with the deposition of torn water droplets on account of water-oil emulsion is achieved a decrease in the volume share of the dispersing phase.

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