Water-in-Oil Emulsions Separation Using a Controlled Multi-Frequency Acoustic Field at an Operating Facility

Abstract

Separation of water-in-oil emulsion is a significant part of the cost of oil production due to the use of expensive demulsifiers and additional heating of the emulsion by burning associated petroleum gas. The article discusses an acoustic method that enables the increasing of the rate of separation of the emulsion. In field conditions, tests were carried out in which the efficiency of separation in the acoustic field was determined depending on the temperature of the product, the concentration of the demulsifier, and the frequency and time of exposure to the emitter. The results obtained allow us to talk about a significant reduction in the consumption of demulsifiers, a decrease in the influence of temperature on the phase separation process and an increase in the efficiency of oil treatment at existing facilities.

1. Introduction

Throughout the history of the oil industry, oil production has been inextricably linked to water production. Water breakthrough is an inevitable part of the process of oil extraction. After water breakthrough, when the level of unprofitability is reached, it is necessary to abandon the well, and early water breakthrough leads to incomplete production of reserves [1]. Moreover, in field experience there are great difficulties associated with the separation of water and oil in the processing of extracted fluids. The destruction of water-oil emulsions requires high temperatures, large dosages of demulsifiers and long retention times. These methods are characterized by high operating and capital costs, metal-intensive processes, and unstable effects on emulsion separation. Therefore, the urgent challenges are to improve existing and develop new effective methods for separating stable emulsions. However, considering the peculiarities of the location of the oil treatment facility in explosive zones, the proposed technical solutions should not consume excessive amounts of electricity and they should also be compact. Recently, the application of physical methods for the separation of stable water-in-oil emulsions has been studied very actively [2,3,4]. Considering peculiarities of applications of electromagnetic influence of waves of high (HF) and ultrahigh frequencies (UHF), the most common, in terms of low values of power consumption, has been determined as ultrasonic influence [5,6]. The materials presented in this article have the following structure. Section 2 shows the main reasons for the formation of emulsions during the development of oil fields and reflects the main methods of their separation. Section 3 presents the conditions necessary for effective ultrasonic exposure to well products, based on the results of laboratory studies and field tests at an oil treatment plant in Western Siberia. Section 3 also describes the influence of temperature factors during oil preparation and the spectrum of ultrasonic exposure on the separation of water-in-oil emulsion. Section 4 summarizes the key factors affecting the efficiency of the separation of emulsions “Water in oil” using a controlled multi-frequency acoustic field at an operating facility.

2. The Main Reasons for the Formation of Oil–Water Emulsions in the Development of Oil Fields and Methods of Their Separation

Stable water-in-oil emulsions (W/OE) are formed in the process of co-production of oil with water [7,8,9,10]. The following processes can be identified as the main causes of emulsion formation during oil field development:

-

Water and oil flow in the reservoir and blowout of formation water into the bottomhole zone of producing wells;

-

Commingling of fluids from multiple reservoirs with different properties;

-

Hydrodynamic influence of working elements of electrical submersible and other submersible pumps when lifting production fluid to the daylight surface;

-

Flow turbulation, as a result of oil degassing during the movement of fluids in the tubing to the daylight surface;

-

Massive application of chemical agents in the oil production system and for inflow stimulation and oil recovery enhancement;

-

Lowering the fluid temperature in the well during production and transportation.

There are a large number of methods for separating stable water-in-oil emulsions, however, the most promising by most researchers are physical methods and, in particular, the use of electromagnetic effects of high (HF) and ultrahigh frequency (microwave) waves. Ultrasonic exposure should also be attributed to effective methods in terms of minimizing power consumption [5,6]. This fact was confirmed as a result of the authors’ field tests.

The test methodology included the deployment of a field laboratory. A room was chosen in which a constant temperature was maintained in the range from +16 °C to +18 °C. The intake of water-in-oil emulsion was carried out every two hours from a specially equipped section of the pipeline from a well bush. A set of W/OE-with periodic (every 6–7 s) splashes of emulsion and subsequent abundant gas release. Gas bubbles have a significant volume and a stable generation period.

The experiment was carried out in accordance with the following measured oil values: density ~ 0.949 g/cm³ (taking into account the gas content of the sample); dynamic viscosity (at T = 20 °C) ~ 40.0 cP; and flow rate in the field pipeline ~ 1 m/s.

3. Methodological Foundations of the Study of the Effectiveness of Ultrasonic Action on the Separation of Water-in-Oil Emulsions

It is known that under the influence of acoustic waves there are attraction and repulsion forces between particles, as well as vibrational oscillations [11]. Nowadays, ultrasound is widely used to accelerate processes such as: dissolution, emulsification, and obtaining suspensions. Ultrasonic vibrations in modes provide superfine dispersion, multiplying the interfacial surface of the components. Dispersion phenomena in the process of ultrasonic exposure occur in cavitation modes. However, it was determined that ultrasonic waves in pre-cavitation modes and low amplitude, can cause resonance oscillations of water globules, which, together with the hydrodynamic mode of flow, will promote accelerated merging and precipitation of water globules, i.e., contribute to the separation into separate phases [12,13,14].

In cooperation with specialists of Gubkin University and Volna LLC, joint research has been conducted for many years in the field of the application of ultrasonic methods in the oil industry [7]. Laboratory facilities were created, which made it possible to conduct research on quasi-static and dynamic models.

The experiments made it possible to determine the behavior of water globules under ultrasonic exposure and to determine the physics of the separation process of W/OE emulsions in an acoustic field, which can be described in the following main stages (Figure 1):

• Under the action of an acoustic field, the level of internal vibrations of water globules increases and the possibility of their collision increases;
• Water globules acquire resonant energy, which leads to fluctuations in the surfaces of globules and their further coagulation;
• When water globules coalesce (their size increases), sedimentation and delamination of the emulsion occur.

In this regard, the purpose of our study was to establish the possibility of increasing the phase separation rate of water-in-oil emulsions (W/OE) under the influence of controlled acoustic multi-frequency fields of a given amplitude in the conditions of a booster pumping station of a field in Western Siberia (Russia) by:

(1)

Resonance of water globules and their further enlargement;

(2)

Using the basics of sound chemistry (exposure to acoustic waves accelerates the kinetics of physico-chemical reactions);

(3)

A significant increase in the contact surface of the injected microdoses of the reagent with the treated medium.

The practical significance of the study lies in the adaptation of the proposed technology to the specifics of a particular deposit. Thus, a feature of the well production collection system in Western Siberia is the significant dependence of the flow properties on seasonal temperature fluctuations. The well-stream has a temperature of plus 35–38 °C (in summer) and minus 25–30 °C (in winter).

In winter, failures in the oil preparation process often occur at the facility under consideration. The extracted well products are heated in furnaces by burning associated petroleum gas. Under these conditions, there is a problem of energy consumption growth with an increase in the water content of products, since the volume of gas entering the installation decreases, and with it the temperature in the heating furnaces also decreases. This necessitated the search for technical solutions to reduce the temperature dependence on the installation facilities.

The main idea is to use typical pipelines of oil treatment plants as resonant channels of ultrasonic waves, contributing to the additional activation of the injected demulsifier for the separation of water-in-oil emulsions (W/OE) and obtaining an additional volume of released gas.

In order to achieve these goals, an extensive complex of experimental work was carried out directly at the subsurface user’s facility with real samples of W/OE (Figure 2).

It should be noted that the oil of the studied field has a complex chemical composition (

Table 1. Properties and composition of the oil of the studied field.

Physical Parameters of Oil	Value at a Temperature of 20 °C
Density (g/cm3)	0.9490
Dynamic viscosity of oil (cP)	40.0
Saturated hydrocarbons (%)	51.1
Aromatic hydrocarbons (%)	34.4
Resins (%)	8.1
Asphalt (%)	4.8
Resins/Asphalt (%)	1.7

). In particular, it has a high viscosity.

The average water content of this deposit is 67%, which forms an abnormal value of the dynamic viscosity of the water-in-oil emulsion entering the installation (in the range of ~2500–3000 MPa*s) and its high stability. These circumstances served as the basis for drawing up a scheme for conducting experiments.

4. Schematic Diagram of the Study of the Effectiveness of Ultrasonic Action on the Separation of Oil and Water Emulsions of a Particular Deposit

The study included two stages: preliminary laboratory studies on modeling the processes of ultrasonic resonant waves (vibrations) of the booster pumping station pipelines; the processes of formation of an industrial layer (nanoemulsion) during W/OE separation; W/OE separation using ultrasonic technologies without the introduction of a demulsifier; and the study of asphaltic resinous paraffine sediments and temperature phase transitions W/OE.

At the second stage, which became the subject of consideration in this article, studies were conducted exclusively with water-in-oil emulsion coming through a field pipeline from wells in the field of Western Siberia (Russian Federation). Based on the field data of the daily volume of processed W/OE (17,000 tons/day), demulsifier consumption (Dissolvan 6070, 180 g/ton), temperature regime, time and hydraulic characteristics of oil and gas separators (OGS), oil preheating furnaces (OH), horizontal settling tanks (HS) for separation of oil and water phases, and technological tanks (VST), a schematic diagram of the experiment was drawn up at the booster pumping station of the field (except for factors related to the release and consumption of gas).

The pipelines were also calculated according to hydraulic, time and temperature parameters of the regime. A number of experiments were carried out in the conditions of the established field laboratory, which made it possible to obtain the dependences of the kinetics of water precipitation W (%) on the main factors, and also the possibility of ultrasonic exposure to solve the problem of effective separation of water-in-oil emulsion was established.

The schematic diagram of the study of the ultrasonic effect on the separation of oil and water emulsions at the field is shown in Figure 3.

According to the scheme, we install active belts of ultrasonic pathogens on the inlet field pipelines. It affects the emulsion before OGS. The water-in-oil emulsion flows from wells through the field pipeline for 8 min into the oil and gas separator of the booster pumping station for degassing. Further, in the reagent dosing unit, the Dissolvan 6070 demulsifier is supplied with a set specific flow rate equal to 180 g per ton. Partially separated and degassed W/OE enters the heating furnace (OH), where it is heated to 40 °C for ~5 min. From there, it goes—to the horizontal sump for 50 min.

It should be noted that with an increase in temperature, the demulsifier begins to provide active water separation at the stage of passing W/OE through the OH coil. The presence of a part of the separated water at the OH inlet and an increase in its share during heating lead to the fact that a significant share of the thermal energy of the furnaces goes to heating the water. At the same time, the temperature of the undivided emulsion is ~4–5 degrees lower. The non-reacted demulsifier is encapsulated in the undivided part of the W/OE and its working efficiency decreases. After heating furnaces, hydrodynamic modes are not enough for active turbulization of OH, especially since the proportion of the dense phase is high. To compensate for this disadvantage, we found it necessary to also install ultrasonic exciters on the outlet pipeline from OGS.

The total length of the pipelines on which active belts of ultrasonic pathogens should be installed was 60 m. The installation step of the active belts is 0.3 m. Thus, 230 active belts with power consumption per 1 active circuit were installed at the level of 14.95 kW per hour. According to the amplitude and frequency ultrasonic effect, the main frequency is ~ 20.9 kHz, since it achieves the best dynamics of water separation W (%) and the maximum reduction in the specific consumption of the demulsifier.

Then, the heated and ultrasonic-exposed W/OE enters horizontal settling tanks (HS) to separate the oil and water phases, from which the oil is sent to process tanks (VST) with a volume of 10,000 m³, where it is prepared in the statistical sedimentation mode. From the VST, the prepared oil is pumped out by external pumping pumps to be sent to consumers.

Control during the experiment was carried out according to the following parameters:

(1)

Water content in oil coming from the field pipeline;

(2)

Its aggregative stability;

(3)

Watering of oil at the outlet of the settling tanks;

(4)

Moisture meter readings;

(5)

Daily consumption of the demulsifier with the ultrasonic exposure system turned on and off;

(6)

The content of residual water in the prepared oil;

(7)

Absence of nanoemulsion growth in the Russia.

The outlet point (1/2” diameter pipe) for sampling is located at the top of the inlet field pipelines. The distance between the W/OE selection site and the DE entry point is 30 m.

The study used a piezoceramic type of pathogen. Before settling on this type of ultrasonic pathogens and developing a scheme for their placement of pathogens on real objects of the deposit, laboratory studies were conducted that took into account a number of circumstances:

(1)

According to Newton’s second law, the strength of a short-term local action of an ultrasonic exciter on a section of pipe with a diameter of 325 mm was determined. At the same time, the mass of the causative agent of ultrasonic vibrations and the mortgage at the level of 0.8–0.9 kg were used as initial data; the amplitude of vibrations was 3–4 microns; the frequency of vibrations was 14.3; 20.9 and 30.4 kHz.

(2)

The first (lowest) were taken into account natural frequencies of vibrations of the pipeline with a diameter of 325 mm [15]. The proposed ultrasonic excitation systems operate at frequencies from 10,000 Hz to 40,000 Hz, and the higher harmonics have an upper range of 200–300 kHz and higher.

(3)

Additionally, the factor of incomplete filling of the pipeline along the W/OE cross section (70%) and the resulting membrane deflections of the pipe under the forceful effects of acoustic exciters in areas where there is gas (they have reduced efficiency in relation to areas where the deflection comes into contact with liquid) was taken into account.

(4)

When choosing the amplitude of the oscillations, the exponential law of attenuation of the amplitude of the ultrasonic wave was applied with increasing distance [16], stating that the wave impact zone in practice should be measured in several centimeters. An attempt to increase the amplitude of vibrations during the experiment led to the appearance of a cavitation regime near the vibration plane, which is unacceptable.

Taking into account all these circumstances, a procedure for conducting experiments was drawn up.

5. The Results Obtained during the Experiment

During the study of samples of oil and water emulsion of the deposit, it was found that globules with an average size of 1.9 microns predominate in the structure of water globules, despite the fact that the mass of water concentrated in them does not exceed 7%. This is the fine-dispersed “negative group” in the composition of the water-in-oil emulsion, which increases its viscosity, resistance to delamination, necessitates the use of an additional volume of demulsifier (which in turn leads to an increase in energy consumption for the separation of W/OE, especially when the temperature changes).

Figure 4 shows microphotographs of W/OE during sampling and the dependence of water globules in the oil during temperature changes without demulsifier. With an increase in temperature, the evolution of the dispersed structure shifts to the coarsening of water globules.

The highest resolution was obtained using an ×40 lens on a microscope, which made it possible to estimate the structure and size of the shell shells on water and oil balls. The analysis of microphotographs (Figure 5) demonstrates the impossibility of gravitational separation of such emulsions. The low value of the dispersing ability of globules explains the additional viscosity of W/OE, increases the resistance to delamination and confirms the need for additional use of a demulsifier or heating.

The influence of temperature factors in the preparation of oil at this installation is well observed in Figure 6, which shows the dependence of water separation on stream temperature in the presence of demulsifier. The demulsifier (DE) input level was assumed to be 100% and 70% of the standard input level at this facility. Tests were conducted at stream temperatures of 30, 35 and 40 °C. It can be seen that with temperature increase, the velocity of water separation improves. It should be noted that at winter temperatures of 30 °C there is a fallout of 94% of water, which leads to the growth of the intermediate phase. This phenomenon explains the failure of product processing at the reviewed object.

Further, the effect of ultrasonic waves on the destruction of water-in-oil emulsions was investigated. It was carried out in beakers made of chemical glass with a volume of 250 mL, at the bottom of which a piezoceramic ultrasonic emitter was fixed. First, an oil-water emulsion was studied without the addition of a demulsifier to initially test the hypothesis of the effectiveness of ultrasonic exposure. During the tests on W/OE, ultrasonic fields with the main harmonics of 14.3; 20.9 and 30.4 kHz were used. The results of the observations are shown in Figure 7.

The level of water separation (W) after 60 s of voicing remained almost constant, since the process of merging globules stops. It is also possible to note the fact of a significant (two-fold) influence of the ultrasound spectrum on the final result. With an increase in the time of ultrasonic exposure and an increase in the settling temperature in the laboratory bath to T = 40 °C, results were obtained confirming the growth of the final indicator W (%). The control sample (without ultrasonic exposure) was also placed in a bath, but did not show any water separation. This suggests that this effect of water separation is initiated by ultrasonic exposure. In addition, this experiment allowed us to choose the frequency of 20.9 kHz as the main one for subsequent studies.

Experiments with laboratory cups allow you to track the entire dynamics of the process of separation of W/OE online. It is possible to simulate various modes of ultrasonic processing by frequency (spectral) composition, wave amplitude (pre-cavitation mode, cavitation mode, etc.).

Additional tests to determine the effect of the ultrasonic spectrum on the degradation of the water-in-oil emulsion during the introduction of DE were carried out at low temperatures and at 70% of the concentration of the injected demulsifier. The test results are shown in Figure 8.

As can be seen from the results of the research (Figure 8), even at low values of temperature (30 °C) and a smaller volume of used demulsifier, it was possible to achieve 100% of water separation at a fundamental frequency of 20.9 kHz.

For industrial application of acoustic oscillations on the chosen object in Western Siberia it is also required to determine the time of ultrasonic influence.

The results of research to determine the effect of ultrasonic exposure time on the degree of water separation of water-in-oil emulsion are shown in Figure 9. The tests were carried out at a temperature of 30 °C using the fundamental acoustic field harmonic-20.9 kHz.

Analysis of the modes shows that with a duration of 20 s and the DE injection rate = 70% (126 g/ton) from the norm (180 g/ton), fluctuations in the hydrodynamic mode bring the water separation time to an indicator of ~ 100 min. That means this mode is a risk zone. Ultrasonic exposure time should be at least 40 s at a demulsifier injection rate of 70%.

In addition, during the experiment, the significant importance of optimizing the hydrodynamic mixing mode during the introduction of a demulsifier was established, since if the water-in-oil emulsion does not move sufficiently, the effectiveness of the demulsifier is sharply reduced. This explains the authors’ attempt to identify various hydraulic modes (stages) and assess their impact on the demulsification process (

Table 2. Hydrodynamic modes of mixing of water-in-oil emulsion isolated during the experiment.

Designation	Explanation	Features
HM1	Hydraulic mode in the main pipe at the point of supply of the demulsifier	Weakly turbulent. Strong viscosity of W/OE, insufficient temperature
HM2	Hydraulic mode in the oil and gas separator of the 1st stage	It is associated with the inflow of oil–water emulsion in the center of the separator (the area of the mirror), the release of gas, the outlet in the lower part of the separator
HM3	Hydraulic mode in heating furnaces	Passage through the furnace coil
HM4	Hydraulic mode in sedimentation tanks	Weakly turbulent, despite the temperature, quasi-static-gravitational settling
HM5	Hydraulic mode in the VST	Quasi-statics-gravitational settling

).

The importance of the correct determination of hydrodynamic regimes is essential for both single-phase media (liquid) and two-phase flows (liquid-gas) [17] not only in the framework of this study in the oil and gas industry, but also in other industries where emulsions are essential (medicine, pharmaceuticals, agriculture, explosives production, polymers, processing of leather raw materials, separation of emulsions during offshore oil production [18,19], others). For the case of a booster pumping station considered in the experiment, obtaining a real picture allows us to assess how effectively the demulsifier can be mixed during insertion (a 1/2” diameter pipeline from the metering pump is embedded on top of the main pipe) in the flow of water-in-oil emulsion.

In the course of the study, it was proved that hydrodynamic regimes in connecting pipelines (except for the HM1 section) certainly affect the dynamics of demulsification, but their influence decreases in those elements of the technological scheme where the residence time of the water-in-oil emulsion increases by 1–2 orders of magnitude. The results obtained made it possible to formulate a program corresponding to the technological scheme of the booster pumping station; to evaluate the time intervals of hydraulic flows of the W/OE and temperature factors in the context of the main technological elements. This program was subsequently taken into account in experimental modeling, but at the first stage, the influence of the hydrodynamic regime on the efficiency of the distribution of the introduced demulsifier into the water-in-oil emulsion (180 g/ton of emulsion (borehole products)) was evaluated, taking into account three modifications of the HM1 regime:

(1)

High-speed hydrodynamics mode without ultrasonic action (P1)—to identify the potential of demulsification (and degassing) only by optimizing the hydrodynamic mode.

(2)

Full hydrostatic mode, mixing is carried out only by ultrasonic action (P2)—in order to establish the effectiveness of ultrasonic activation of the demulsifier in the case when it is impossible to control the hydrodynamic process (evaluation of the effect of ultrasound «from below», in the worst case).

(3)

Mixed mode (slow hydrodynamics and ultrasonic action) (P3)—the existing hydrodynamic mode with the additional use of ultrasonic action (activation).

Figure 10 shows the dependence of the water separation index (W, %) on the simulation of the HM1 mode, that is, the hydraulic mode at the time of entering the demulsifier in the field pipeline. The control sample (100% demulsifier was introduced) during the observation showed an inflated layer at the bottom of the beaker without visible separation into phases, which was interpreted as an industrial layer (nanoemulsions).

The P2 variant of the HM1 mode after the introduction of the demulsifier was modeled by weak manual stirring of the emulsion (№0), then the number of revolutions of the agitator was increased taking into account the correspondence of the linear speed of the propeller agitator (R = 2.5 cm) by the ratio V = w*R to 400 (№1) − 1000 (№ 2, 4) revolutions/min with stirring time ~20 s (the time of movement of the oil-water emulsion through the field pipeline from the input of the demulsifier to the booster pumping station to the entrance to the gas separator). The revolutions were chosen so that at 400 rpm the speed was close to linear ~1 m/s, and at 1000 rpm the speed had to simulate a turbulent flow at the time of delivery of the demulsifier (~2.5 m/s).

After entering the separator, the hydraulic mode changes from HM1 to HM2, which significantly affects the processes of phase separation. At the same time, there was a slight difference between the speeds of rotation of the agitator 400 rpm and 1000 rpm and a sharp deterioration in separation when the mixing process tends to a weak mode. This leads to an important conclusion that despite the assumed linear flow rate of the water-in-oil emulsion in the main pipe in the range of 0.7–1.0 m/s, intense turbulent mixing does not occur at the time of injection, including due to the rheological properties of the emulsion.

It is very interesting to study the variant P2 of the HM1 mode, when the dispersion of the introduced demulsifier occurs only under ultrasonic influence. For comparison, it is convenient to show these dependencies simultaneously with the P1 mode (Figure 11). Hydrodynamic mode (above average) according to its dispersing properties under analogous conditions of the control sample, it turned out to be approximately equal to the ultrasonic effect in the full hydrostatic mode. However, there is a weak influence of the temperature of the water-in-oil emulsion (between 26 °C and 32 °C) on the W (%) index. The separation level at P2 is either equal to or higher than that of the P1 mode (pure hydrodynamics). In the regime of strong hydrodynamics (practically unrealizable), a similar effect was observed on the final separation of the emulsion.

The depicted dependencies are interpreted as follows. With a short ultrasonic exposure (less than 20 s), the main mode will be the low-efficiency hydrodynamic mode P1. With an increase in the duration of exposure to 30–40 s, the influence of the hydraulic mode on the dispersion of the demulsifier decreases rapidly, and with the ultrasonic exposure time up to 50 s, the hydraulic mode P1 ceases to play a role in this process, that is, its contribution becomes insignificant and all changes in hydraulic modes (from the point of view of the dispersing effect) are compensated only by a subsequent increase in the exposure time. In addition to avoiding the influence of turbulence of hydrodynamic factors, there is a weak dependence of the degree of dispersion of the demulsifier in the emulsion on temperature. Multi-frequency acoustic ultrasound waves cope with the dispersion function significantly better than turbulent hydraulic flows.

In general, it is worth noting that with the uncertainty of input such parameters as: hydraulic modes and their turbulence; emulsion temperature; percentage of the demulsifier input and, possibly, the quality of its chemical composition, the ultrasonic exposure time should be in the range of 30–60 s. Such a duration allows for the practical implementation of ultrasonic activation systems both on existing main pipelines and in the form of separate modules’ phase separators. In the latter case, it is necessary to pair the input point of the demulsifier with the phase separator module to achieve maximum dispersion efficiency.

During laboratory work, the influence of the frequency and spectral composition of ultrasonic exposure on the kinetics of water separation W (%) was also revealed. This issue should be taken into account if the phase divider is designed as a separate module and the configuration of the resonant channel section should be chosen in order to optimize the characteristics of the frequency spectrum of the impact.

6. Key Factors Affecting Efficiency W/OE Separation Using a Controlled Multifrequency Acoustic Field at an Operating Facility

Based on the results of laboratory studies and the works of various researchers [20,21,22,23,24,25], a number of physical parameters have been identified that most significantly affect the kinetics of phase separation of the water-in-oil emulsion, namely: chemical composition of the deposit emulsion; its dispersed structure and water content; viscosity and temperature of the W/OE; percentage of input and chemical composition of the demulsifier; time of complete water loss (criterion W > 93%); duration of ultrasonic exposure (seconds) and its spectral composition; the hydrodynamic regime of the flow of W/OE; and gas content (Figure 12). In particular, the introduction of a demulsifier affects both the separation of the phases of the emulsion and, by reducing the surface tension, contributes to an increase in the gas output from the W/OE, starting with the degassing stage in the separator. Intensive gas release, in turn, contributes to the activation of the encapsulated demulsifier, etc. The viscosity index of the emulsion, which practically does not change when moving in the pipeline, is of great importance, since the viscosity of Newtonian liquids does not depend on the shear rate, but it increases sharply with an increase in the concentration of the dispersed phase (oil droplets).

The viscosity of the water-in-oil emulsion in the simulation was described using the equation [26]:

$${\mathsf{\mu }}_r={\left[1-\left\{1+\left(\frac{1-{\mathsf{\phi }}_m}{{\mathsf{\phi }}_m^2}\right)\mathsf{\phi }\right\}\mathsf{\phi }\right]}^{-2.5}$$

(1)

where φ_m—is the maximum volume fraction of homogeneous particles in the emulsion.

Taking into account that the water-in-oil emulsion consists of inhomogeneous particles in size, a value of φ_m equal to 0.85 was used in the simulation. This is especially important, since with an increase in the viscosity of the emulsion, the rate of exergetic destruction [26] also increases, which leads to an increase in energy consumption, the optimization of which is part of the research objectives.

These factors are interrelated. In particular, the introduction of a demulsifier affects both the separation of the phases of the emulsion and, by reducing the surface tension, contributes to an increase in the gas output from the W/OE, starting with the degassing stage in the separator. The intense release of gas, in turn, contributes to the activation of the encapsulated demulsifier, etc. In this regard, of particular interest is the choice of the method of fastening ultrasonic exciters on the main pipeline, considering the attenuation of the acoustic wave in a liquid medium. Two fastening options were tested at the field, which were called T-shaped and “cross” (Figure 13).

“Scheme T” has been tested on pipelines where the hydraulic flow mode assumes the presence of a “gas cap” in the upper part of the pipe. In this case, the membrane deflections of the pipe from the upper ultrasonic exciter according to the “cross” scheme fall on gas, which reduces the efficiency of the exciter. The mathematical proof of this is a simple calculation of the length of the ultrasonic wave propagating through the shell of the pipe. At an elastic wave velocity of ~5800 m/s, for a frequency of 20.9 kHz, the wavelength will be ~30 cm. This is the interval of the location of the active zones of ultrasonic pathogens along the length of the pipe. In general, the experiments have shown that the excitation schemes are almost identical, but from the point of view of practical implementation, the T-shaped scheme is preferable (through special mortgages, the installation of which is carried out using a non-welded fastening technology).

The need to take into account all these factors and their mutual influence once again confirms the relevance of experimental modeling [27,28,29] of technological processes with the help of a field laboratory that allows simulating existing operating modes; to assess the contribution of ultrasonic exposure, the depth of positive factors; to make a sound feasibility study of the effectiveness of the proposed method. In addition, modeling allows you to achieve the following advantages:

(1)

High reliability of modeling and obtaining experimental data, the possibility of their comparison with the real readings of the object;

(2)

Specification of technological modes, schemes, the resulting effect in physical and cost terms;

(3)

Low cost of field audit, efficiency, and high efficiency.

The issue of technology efficiency is one of the main ones in our study. To do this, the characteristics of the destruction of the high-pressure emulsion were studied for different durations of exposure to an ultrasonic pathogen. The effectiveness was determined by comparing the dynamics of separation of water in the sample of the W/OE coming through the field pipeline to the booster pumping station in relation to control samples with a decrease in the amount of demulsifier after ultrasonic exposure (Figure 14).

Based on the results of studies conducted with W/OE, the schedule for reducing the consumption of the Dissolvan 6070 demulsifier used at the deposit is reflected in Figure 15, from which it can be seen that a 50% reduction in the specific consumption of the demulsifier was achieved in a short period of time. Taking into account the total volume of processed emulsion per day (17,000 tons) and the demulsifier consumption rate (180 g/ton), the total reduction in operating costs for the booster compressor station for 5 months of the study amounted to 22 million rubles (taking into account the increased energy costs for the operation of ultrasonic shock belts).

In addition, studies have revealed a number of other effects resulting from ultrasonic separation of the emulsion: reduction in gravity deposition time; reduction in the formation of an intermediate layer in the tank; and reduction in the residual content of hydrocarbons in the water.

Taking into account all of the above, the general efficiency criterion for the research task is formulated as follows: the maximum efficiency of dispersion of a small physical volume of a demulsifier when a water-in-oil emulsion is introduced into the volume and further temporary synchronization of thermal, hydrodynamic and chemical processes with each other. The implementation of the project at this stage (Figure 16) made it possible to partially achieve this criterion at the booster pumping station of the field in Western Siberia.

The main results of the industrial application of the technology were: increasing the efficiency of field oil treatment and reducing dependence on seasonal fluctuations in ambient temperature by installing ultrasonic impact belts on the main lines from the point of introduction of the demulsifier and after the separator before entering the oil heating furnaces. In total, the project uses 230 active ultrasonic impact belts, with a total power consumption of 14.9 kW/hour. At the same time, the costs of the demulsifier are minimal.

7. Summary

(1)

A field laboratory has been developed and tested, which allows to obtain and simulate the main characteristics of the technological cycle directly at oil production and primary oil treatment facilities, both without ultrasonic exposure, and with improvement of technological cycle parameters, using ultrasonic technologies for activating the injected demulsifier.

(2)

At the moment, the field laboratory is designed as mobile modules and can be quickly deployed in any fixed enclosed area with a standard power supply.

(3)

A methodology for performing field work at existing facilities has been developed. The lists of input data, the sequence of work execution and experimental modeling of technological processes have been determined.

(4)

The regularities of the kinetics of phase separation for temperatures of 30 and 40 °C with a demulsifier injection volume of 30, 40, 50 and 70% from normal on actual water-in-oil emulsions have been investigated and the main parameters of physical fields application, applied to a specific oil processing unit, have been determined.

(5)

W/OE separation modeling was performed to evaluate the performance of the target objectives in relation to an oil field. It was determined that under the existing technological scheme of booster compressor station, the priority option of placing the section of ultrasonic activation of injected demulsifier is the section of the pipeline in front of the point of DE input to the inlet to the gas separator OGS and after it. In this case, the duration of the ultrasound exposure should be at least 40 s.

In conclusion, it should be noted that the proposed technology increases the productivity of existing BCS, as well as significantly reduces the capital costs of equipment for primary oil treatment plants at new onshore and offshore facilities.