Study of the rheological properties of high-viscosity oil from the Pechersk field. Coursework: Methods for developing deposits of high-viscosity oils and natural bitumen

Farmanzade A.R. 1, Karpunin N.A. 2, Khromykh L.N. 3, Evsenkova A.O. 4, Al-Ghobi G. 5

1 PhD student, 2 student, 3 associate professor, 4 student, 5 student. 1,2,4,5 National Mineral Resources University "Mining", 3 Samara State Technical University

STUDY OF RHEOLOGICAL PROPERTIES OF HIGH-VISCOSITY OIL OF THE PECHERSKY FIELD

annotation

The article studies the rheological properties of heavy oil from the Pechersk field in a wide temperature range. The main attention is paid to the study of the viscous and elastic components of viscosity depending on temperature to substantiate the optimal conditions for the development of a given oil field.

Keywords: high-viscosity oil, bitumen, elastic viscosity component, viscous viscosity component, rheological properties.

Farmanzade A. R. 1 , Karpunin N. A. 2, Khromykh L.N. 3,Evsenkova A. O. 4 , Al– Gobi G. 5

1 Postgraduate student, 2 students, 3 associate professor, 4 students, 5 students. 1,2,4,5 National Mineral Recourses University (University of Mines), 3 Samara State Technical University

THE INVESTIGATION RHEOLOGICAL PROPERTIES OF HEAVY OIL FIELD PECHORA

Abstract

There is the investigation of the rheological properties of heavy oil field Pechora in a wide temperatures range in this paper. Main attention is given to the study of thelossandstoragemodulus of the viscosity as a function of temperature for the recommendation of optimal conditions for development of this oil field.

Keywords: heavy oil, bitumen, storage modulus, loss modulus, rheological properties.

Today, due to the steady depletion of reserves of light, low-viscosity oils, the need to introduce into the development of fields hard-to-recover reserves, such as high-viscosity oils and natural bitumens, most of which are located in Canada, Venezuela and Russia, is becoming increasingly important. In the Russian Federation, more than 70% of high-viscosity oils are confined to 5 regions: in the Perm region (more than 31%), in Tatarstan (12.8%), in the Samara region (9.7%), in Bashkortostan (8.6%) and Tyumen region (8.3%).

Oil deposits of this type are, as a rule, characterized by shallow depths of oil-bearing strata and, often, low reservoir temperatures, while the oils or bitumens contained in them have non-Newtonian properties due to the high content of paraffins, asphaltenes and resins. With a high content of heavy components in the composition of oils, viscoelastic properties appear, which were first discovered back in the 1970s. .

The high viscosity values ​​of such oils in reservoir conditions are the reason for the low flow rates of production wells, and sometimes even their complete absence when trying to develop the field in a natural mode. Currently, thermal methods of influencing the productive formation are most widespread in the development of deposits of such hydrocarbons. Among these technologies, it is worth noting cyclic steam injection and area steam injection, as the most common methods of production and intensification in Russia, and steam assisted gravity drainage (SAGD), widely used abroad.

To study the properties of high-viscosity oil located in a complex carbonate reservoir, the Pecherskoye field, located on the banks of the Volga River, near the village of Pecherskoye, was selected. Previously, rocks (limestones and dolomites) saturated with heavy oil were mined at this field for the subsequent extraction of raw materials from it for the production of bitumen mastic. The authors organized field trips to this field to collect information about the structure of the deposit and samples to study the rheological properties of oil and the void space of the reservoir.

In this work, the rheological properties of oil depending on temperature were studied. In this case, a modern high-precision rotational viscometer with air bearings was used.

An experiment to study the dependence of dynamic viscosity on temperature was carried out as follows: a drop of oil with a volume of 1 ml was placed on a viscometer platform heated to 70°C, then the drop was pressed by a rotor, and the temperature increased to 110°C. The angular velocity was set on the viscometer to 5 s -1 , after which the temperature gradually dropped to 50°C. This temperature was proposed as a limit to prevent excessive overload of the viscometer motor.

Rice. 1 – Dependence of dynamic viscosity of high-viscosity oil on temperature.

The presented figure shows that the dynamic viscosity of oil can be described by a power function of the form y=1177320551696170000x -7.24 with an approximation reliability value of R² = 0.99554. Oil is highly viscous throughout the entire range of temperatures presented (viscosity at 110°C is 2003 mPa∙s, and at 50°C – 502,343 mPa∙s). At this stage of testing, it was not possible to measure the viscosity of oil at a reservoir temperature of 20°C due to limitations in the capabilities of the viscometer.

To further study the rheological properties of this oil, additional specialized dynamic tests were carried out to determine the elastic and viscous components of viscosity. During the experiments, the effect of decreasing temperature on the elastic component of viscosity (dynamic shear modulus, also called storage modulus) and the viscous component of viscosity (compliance or loss modulus) was studied. In the first case, the oil from the Pechersk field used for research was cooled in the selected temperature range from 90ºС to 50ºС. The experiment proceeded as follows: a drop of oil with a volume of 1 ml was placed on a viscometer platform heated to 70°C, then the drop was pressed with a rotor, and the temperature increased to 90°C, after which it gradually decreased to 50°C with data recording. The dynamic load was represented by the oscillatory movement of the rotor with a frequency of 1 Hz and a load of 100 Pa. The results are presented in Figure 2.

Rice. 2 – Dependence of elastic (storage modulus) and viscous (loss modulus) components of viscosity of high-viscosity oil from the Pecherskoye field on temperature.

Analyzing the presented dependencies, it is possible to draw the following conclusions: firstly, both the viscous and elastic components of oil viscosity decrease with increasing temperature and reach relatively small values ​​at 80°C, which proves the need to use thermal energy in the development of this field. Secondly, it is noticeable that in the studied temperature range oil has elastic properties, which, although they decrease with increasing temperature, reach significant values: 23.54 Pa.

Based on the results of the research, it is possible to draw the following conclusions:

1. High-viscosity oil from the Pecherskoye field is characterized by abnormally high viscosity: the measured dynamic viscosity at 50°C is 502343 mPa∙s.
2. Based on the fact that the viscosity of oil with an increase in temperature from 50 to 110°C decreases from 502343 mPa∙s to 2000 mPa∙s, in order to extract oil from the rock of this field, it is necessary to use thermal action.
3. The studied oil has complex rheological properties, probably due to the high content of asphaltenes and resins characteristic of near-surface fields in the Samara region. High values ​​of the viscous and elastic viscosity components are observed throughout the entire temperature range at which dynamic tests were carried out, which will undoubtedly have a negative impact on the process of oil extraction from the reservoir.
4. The authors of the work plan further tests aimed at justifying effective technologies for extracting such anomalous oils from productive formations, for example, technologies using complex effects of thermal agents and solvents.

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Ministry of Education and Science of the Russian Federation

Federal budgetary state educational institution of higher professional education

"Ufa State Petroleum Technical University"

Department of “Construction and repair of gas and oil pipelines and gas and oil storage facilities”

transportation of high-viscosity oil

abstract

INTRODUCTION

Pumping of highly viscous and highly solidifying oils

Hydrotransport of highly viscous oils

Pumping of heat-treated oils

Pumping oils with additives

Pumping of preheated oils

Pumping method by cavitation action

CONCLUSION

INTRODUCTION

A characteristic feature of modern oil production is the increase in the global structure of raw material resources in the share of hard-to-recover reserves (TIR), which include heavy oil with a viscosity of 30 mPa*s and higher. Reserves of such types of oil amount to at least 1 trillion. tons, which is more than five times the volume of remaining recoverable oil reserves of low and medium viscosity. In many industrialized countries of the world, heavy oil is considered as the main basis for the development of oil production in the coming years. The largest reserves of heavy and bituminous oil are located in Canada and Venezuela, as well as Mexico, the USA, Kuwait, and China.

Russia also has significant oil and gas reserves, and their volume accounts for about 55% of the total Russian oil reserves. Russian fields of high-viscosity oil (HVO) are located in the Perm region, Tatarstan, Bashkiria and Udmurtia. The largest of them are: Van-Eganskoye, Severo-Komsomolskoye, Usinskoye, Russkoye, Gremikhinskoye, etc., with more than 2/3 of all high-viscosity oil reserves located at depths of up to 2000 m. Production of TIZ oil, its transportation to collection and treatment points and, finally, processing to obtain final products is one of the urgent tasks of the oil industry. There are various methods for pipeline pumping of high-viscosity oils.

Currently, significant volumes of oils are produced that have high viscosity at ordinary temperatures or contain large amounts of paraffin and, as a result, solidify at high temperatures. Pumping such oils through pipelines in the usual way is difficult. Therefore, special methods are used for their transportation:

pumping with diluents;

hydrotransport of high-viscosity oils;

pumping of heat-treated oils;

pumping oils with additives;

pumping of preheated oils.

Pumping of highly viscous and highly solidifying oils with diluents

One of the effective and affordable ways to improve the rheological properties of high-viscosity and highly solidifying oils is the use of hydrocarbon diluents - gas condensate and low-viscosity oils.

The use of thinners can significantly reduce the viscosity and pour point of oil. This is due to the fact that, firstly, the concentration of paraffin in the mixture decreases, since part of it is dissolved by the light fractions of the diluent. Secondly, if there are asphalt-resinous substances in the diluents, the latter, being adsorbed on the surface of paraffin crystals, prevent the formation of a strong structural lattice.

The first experiments in our country on pumping oils with a diluent (kerosene distillate) were carried out by engineers: A. N. Sakhanov and A. A. Kashcheev in 1926. The results obtained were so impressive that they were used in the design of the Grozny-Black Sea oil pipeline " Currently, pumping highly viscous and highly solidifying oils with diluents is widely used in our country and abroad. For example, highly paraffinic Manyshlak oil is pumped to the Samara region in a heated state, and then mixed with low-viscosity oils of the Volga region and pumped into the Druzhba oil pipeline.

In general, the choice of the type of diluent is made taking into account the effectiveness of its action on the properties of high-viscosity and high-solidifying oil, the costs of obtaining the diluent, its delivery to the head structures of the oil pipeline and for mixing.

It is curious that the geological properties of the oil mixture are influenced by the temperature of the mixed components. A homogeneous mixture is obtained if mixing is carried out at a temperature 3-5 degrees above the pour point of the viscous component. Under unfavorable mixing conditions, the effectiveness of the thinner is significantly reduced and even separation of the mixture may occur.

2. Hydrotransport of highly viscous oils

Hydrotransport of highly viscous and highly solidified oils can be carried out in several ways:

pumping oil inside a water ring;

pumping a water-oil mixture in the form of an “oil in water” emulsion;

layer-by-layer pumping of oil and water.

Figure 1 - Hydropumping of oil inside a water ring:

a - using screw threads; b - using ring couplings; c - using a perforated pipeline.

Back in 1906, I. D. Isaac carried out pumping of high-viscosity (n = 25) in the USA 102 /c) California oil with water through a pipeline with a diameter of "6 mm to a distance of 800 m. A spirally coiled wire was welded to the inner wall of the pipe, providing a swirl of the flow (Figure 1). As a result, heavier water was thrown directly to the wall, and the oil flow moved inside the water ring, experiencing minimal friction.It was found that the maximum productivity of the pipeline at a constant pressure drop was achieved at a ratio of oil and water flow rates equal to 9: 1. The results of the experiment were used in the construction of an industrial oil pipeline with a diameter of 203 mm and a length of 50 km. it had a height of 24 mm and a pitch of about 3 m.

However, this method of transport has not received wide distribution due to the complexity of manufacturing screw threads on the inner surface of pipes. In addition, as a result of paraffin deposition, the thread becomes clogged, the water ring is not formed near the wall, which drastically worsens the pumping parameters.

The essence of another method of hydrotransport is that high-viscosity oil and water are mixed before pumping in such a proportion that an oil-in-water emulsion is formed (Figure 2). In this case, the oil droplets are surrounded by a water film and therefore there is no contact between the oil and the pipe wall.

Figure 2 - Hydropumping in the form of an emulsion:

a - “oil in water” type; b - “water in oil” type

To stabilize emulsions and impart hydrophilic properties to the pipeline walls, i.e. the ability to retain water on its surface, surfactants (surfactants) are added to them. The stability of an oil-in-water emulsion depends on the type and concentration of surfactants, temperature, flow regime, and the ratio of water and oil in the mixture.

Reducing the volume of mica in the mixture worsens the stability of the emulsion. As a result of the experiments, it was found that the minimum allowable water content is exactly 30%.

The disadvantage of this method of hydrotransport is the danger of phase inversion, i.e., the transformation of the oil-in-water emulsion into a water-in-oil emulsion when the pumping speed or temperature changes. Such an emulsion has a viscosity even greater than the viscosity of the original oil. In addition, when the emulsion passes through the pumps, it is pumped very intensively and subsequently it is difficult to separate it into oil and water.

Finally, the third method of hydraulic transport is layer-by-layer pumping of oil and water (Figure 3). In this case, water, as a heavier liquid, occupies a position at the lower generatrix of the pipe, and oil - at the top. Depending on the pumping speed, the phase interface can be either flat or curved. A decrease in the hydraulic resistance of the pipeline in this case occurs due to the fact that part of the oil is in contact not with a stationary wall, but with moving water. This pumping method also cannot be used on pipelines with intermediate pumping stations, because this would lead to the formation of persistent oil-water emulsions.

Figure 3 - Structural forms of water-oil flow during layer-by-layer pumping of oil and water: a - lens; b - separate with a flat border; c - separate with a curved border; g - annular eccentric; d - ring concentric

Each structural form of flow is established spontaneously as soon as the conditions for its existence are achieved.

Relationship between the structural forms of oil-water flow and the magnitude of the hydraulic slope. According to experimental studies by F.M. Galin, it is as follows (Figure 4).

Figure 4 - Dependence of hydraulic slope on flow rate when pumping a mixture of oil and water

3. Pumping of heat-treated oils

Heat treatment is the heat treatment of highly paraffinic oil, which involves heating it to a temperature exceeding the melting point of paraffins, and subsequent cooling at a given speed to improve rheological parameters.

The first experiments in our country on heat treatment of oils were carried out in the 30s. Thus, heat treatment of oil from the Romashkinskoye field made it possible to reduce its viscosity by more than 2 times and reduce the pour point by 20 degrees.

It has been established that the improvement in the rheological properties of oils is associated with internal changes in them that occur as a result of heat treatment. Under normal conditions, when paraffin oils naturally cool, a crystalline paraffin structure is formed, which gives the oil the properties of a solid. The strength of the structure turns out to be greater, the higher the concentration of paraffin in oil and the smaller the size of the resulting crystals. By heating oil to a temperature higher than the melting point of paraffins, we achieve their complete dissolution. Upon subsequent cooling of the oil, crystallization of paraffins occurs. The size, number and shape of paraffin crystals in oil are influenced by the ratio of the rate of occurrence of paraffin crystallization centers and the growth rate of already formed crystals. Asphalt-resinous substances, adsorbed on paraffin crystals, reduce its surface tension. As a result, the process of paraffin release on the surface of existing crystals becomes energetically more favorable than the formation of new crystallization centers. This leads to the formation of fairly large paraffin crystals in heat-treated oil. At the same time, due to the presence of adsorbed asphaltenes and resins on the surface of these crystals, the coagulation adhesion forces between them are significantly weakened, which prevents the formation of a strong paraffin structure.

Figure 5 - Restoration of the effective viscosity of Ozeksuat (1) and Zhetybay (2) oils over time after heat treatment

The effectiveness of heat treatment depends on the heating temperature, cooling rate and the state of the oil (static or dynamic) during the cooling process. The optimal heating temperature during heat treatment is determined experimentally, the best cooling conditions are static.

It should be borne in mind that the rheological parameters of heat-treated oil deteriorate over time and eventually reach the values ​​that the oil had before heat treatment (Figure 5). For Ozeksuat oil this time is 3 days, and for Mangyshlak oil - 45. So it is not always enough to thermally treat oil once to solve the problem of its pipeline transport. In addition, capital investments<#"214" src="/wimg/16/doc_zip7.jpg" />

Figure 6 - Schematic flow diagram of “hot” pumping

As the oil moves through the main pipeline, it cools due to heat exchange with the environment. Therefore, heating points are installed along the pipeline route every 25-100 km. Intermediate pumping stations are placed in accordance with hydraulic calculations, but must be combined with heating points to facilitate their operation. Ultimately, the oil is pumped into the final destination tanks, which are also equipped with a heating system.

Oil is pumped through “hot” pipelines using conventional centrifugal pumps. This is due to the fact that the temperature of the pumped oil is quite high, and therefore its viscosity is low. When pushing cooled oil out of pipelines, piston pumps, for example NT-45, are used. To heat oil, radiant-convection furnaces are used, the efficiency of which reaches 77%.

But almost all main oil pipelines are non-isothermal. The viscosity of the pumped oil, the hydraulic resistance of the pipeline, the flow Q and the pressure P of centrifugal pumps (CPP) depend on the temperature. Consequently, the cost of pumping also depends on the temperature regime of the pipeline. Therefore, the calculation of operating conditions for summer and winter conditions, quasi-stationary and non-stationary, must be carried out taking into account the heat exchange of the pipeline with the environment. Non-isothermal flow can be caused by various reasons:

The temperature of viscous oil can increase as it travels between pumping stations due to the release of friction heat. Analysis of factual material on 19 main pipelines, including the oil pipelines Druzhba, Shaim - Tyumen, Aleksandrovskoye - Anzhero - Sudzhensk, Ust - Balyk - Omsk, oil pipelines of Western and Northwestern Siberia, Verkhne - Volga, oil pipelines Tebuk - Ukhta, Usa - Ukhta et al., revealed obvious, 1.5-2 times relative to the average, changes in the heat transfer coefficient. This fact also indicates the non-stationary nature of heat exchange between pipelines and the environment. The instability of the thermal-hydraulic regimes of main oil pipelines leads to excessive energy consumption for pumping and excess operating costs.

When oil is pumped into a pipeline with a temperature different from the ambient temperature along the route, a non-isothermal initial section is formed, the length of which can be comparable or equal to the length of the stage between pumping stations. Oil extracted from the depths of the Earth, treated with additives (the temperature at which additives are introduced is about 50...70°C) or has undergone a special heat treatment that improves its transportable properties, is pumped in a non-isothermal mode. Since the temperature conditions of the initial sections of pipelines are unstable and strongly depend on climatic conditions, the thermal-hydraulic calculation of such sections must be carried out taking into account unsteady heat exchange. A typical situation has developed on the Kumkol - Karakoin oil pipeline of the Eastern branch of NKTN KazTransOil. In conditions of deep underload in terms of productivity, the calculation of operating modes and justification of methods for pumping viscoplastic oil with thixotropic properties is very problematic. The introduction of depressant additives into the flow requires heating of the oil and makes pumping oil through the pipeline non-isothermal. It should be noted that the use of additives does not solve the problem. During cold winter periods, situations arise when it is impossible to pump oil. In the conditions of Central Asia, the method of “hot” pumping of Kumkol oils, which does not require expensive additives, may turn out to be economically profitable. It should be noted that there is extensive experience in operating under similar conditions the largest “hot” oil pipeline of large diameter (720-1020 mm) Uzen - Guryev - Kuibyshev, through which highly solidified Mangyshlak oil was pumped with a pour point tз = 28 °С and a heating temperature tн = 65 °C. Currently, this pipeline is also non-isothermal, but operates at low temperatures, about 30 ° C, since the mixture of oils passing through the pipeline has moderate viscosity. With an increase in the proportion of high-viscosity oils, the pumping temperature will correspondingly increase. For the main oil pipeline Usa - Ukhta, through which highly solidified oils of the Timan - Pechersk oil and gas province with the addition of depressant additives are pumped, the problem of calculating and justifying the modes of pumping oils through the pipeline is also acute. The fact is that the share of heavy and highly paraffinic oil, which has viscoplastic properties, will in the future fluctuate between 37...56%, and the use of depressant additives may not give the expected effect. The "hot" pumping method is currently considered as an alternative.

Particularly difficult are the calculations of “hot” pipelines, through which pumping of highly viscous and highly solidifying liquids is carried out at higher temperatures, on the order of 60-120 °C. During “hot” pumping, oil is heated in the furnaces of intermediate thermal stations, which not only increases the cost of pipeline transport of oil or petroleum products, but also poses specific problems of reliability and environmental safety of the system. Since heated oil cools down over time, and specially treated oil loses its temporarily improved transportable properties, the following must be calculated for both “hot” and any non-isothermal pipelines:

) time of safe shutdown and starting parameters of centrifugal pumps (flow Q and pressure P) at the time of resumption of pumping;

) heating time of the pipeline τpr when starting it from a cold state;

) the time of safe operation of the pipeline τbr at reduced conditions (with a temporary decrease in pump flow, a decrease in the heating temperature of the pumped oil, etc.).

When calculating the operating modes of non-isothermal pipelines, it is necessary to take into account the fact that such systems practically do not operate in design modes for a number of reasons, such as climatic changes in the environment (temperature, soil properties, etc.), seasonality of system loading, phased commissioning of capacities , aging and wear of equipment, loss of productivity due to depletion of deposits, changes in cargo flows, etc. Therefore, for both “hot” and simply non-isothermal pipelines, characterized by less intense heat transfer, there is a real danger of the pipeline “freezing” or the supply being “dropped” due to an excessive increase in hydraulic resistance. Therefore, increased requirements are placed on thermal-hydraulic calculations of such pipelines. In addition to the usual design thermal-hydraulic calculations, it is necessary to perform calculations of non-stationary modes, such as starting, stopping and resuming pumping. Dynamic characteristics can be plotted for liquids with different rheological models. The great advantage of this method is that it allows one to take into account changes in the supply of centrifugal pumps due to changes in the hydraulic resistance of the pipeline. When using the appropriate computer program, it becomes possible to take into account changes in other pumping and heat transfer parameters.

Currently, more than 50 “hot” main pipelines are in operation around the world. The largest of them is the Uzen-Guriev-Kuibyshev oil pipeline.

6. Method of pumping by cavitation action

Of great interest are the results of an experimental study of changes in oil viscosity by cavitation action using a method in which a device is proposed that contains a hollow cylindrical body of variable cross-section in a pipeline line, including a smooth narrowing that ensures the occurrence of cavitation. High-amplitude oscillations in the liquid are cavitation bubbles with high speed, due to which the viscosity of the oil decreases.

A cavitation module for processing paraffinic oil can be calculated in order to reduce its viscosity, on the basis of which a hydrodynamic flow installation has been developed and tested. Experiments showed that after sonochemical treatment of oil, the viscosity of oil was reduced by 35%.

The main disadvantage of this device is the intense cavitation wear of its working surfaces, generating (from the embryonic nuclei) cavitation bubbles, most of which collapse on these surfaces. Another disadvantage is the weak degree of regulation of the intensity of cavitation treatment, since the number of cavitation nuclei in the original oil is difficult to regulate. In addition, the sizes of cavitation bubbles formed in such devices, on which the intensity of cavitation-cumulative treatment mainly depends, are also practically impossible to regulate. The residence time of the cavitation core in the rarefaction zone, necessary for the formation of a bubble of the required size, in such devices can vary within very small limits and is associated with the frequency of pulsations, vibrations, etc. The main parameter that determines the kinetics of cavitation action is the initial (before collapse) size cavitation bubbles can vary within very narrow limits and are often far from the maximum. The listed disadvantages are negatively manifested in treated oil - a slight decrease in viscosity, short time of thixotropic recovery.

Analysis of studies on the use of ultrasonic and hydrodynamic cavitation in oils for the intensification of various technological processes shows the promise of this method. However, ultrasonic cavitation has not found wide application in enterprises with large production volumes for a number of reasons: significant energy costs for the generation of cavitation bubbles, sharp attenuation of ultrasonic waves in technological suspensions, limitation of local exposure to the vibration zone of the radiating surface, destruction of working surfaces by cavitation, etc.

CONCLUSION

The most studied and widespread method of transporting high-viscosity oils at present is their “hot pumping” through pipelines. Despite the fact that this is the most mature technology, it has serious drawbacks. First of all, it is high energy intensity, because... As a rule, the transported medium itself is used as fuel during heating - valuable chemical raw materials and fuel (oil, fuel oil).

The second difficulty is related to the fact that under unfavorable weather conditions the pipeline may “freeze”. Finally, the construction of such pipelines in areas with frozen and planted soils is difficult for environmental reasons due to the difficulty of ensuring structural reliability and complications in construction technology.

LIST OF SOURCES USED

1Korshak, A.A. Design and operation of gas and oil pipelines / A.A. Korshak, A.M. Nechval. - St. Petersburg: Nedra, 2008. - 488 p.

Harris, N.A. Construction of the dynamic characteristics of the main pipeline (viscoplastic fluid model) // Oil and Gas Business. - 2014. - No. 1. - P. 10-13.

Oil is still an indispensable mineral used in many areas of human activity. Even despite successful attempts to find an alternative to it, oil still remains a very popular product. This leads to the fact that the extraction of oil reserves from the bowels of the earth is carried out at a colossal pace, and therefore oil deposits are very quickly reduced, without having time to form again. Thus, conventional oil, also called light oil, is being replaced by heavier oil.

It is worth noting that absolutely all oil reserves in the world are classified according to their density. Thus, oil is usually divided into the following types:

1. Super light oil. It is distinguished by its low density, which is less than 0.780 g/cm3 and API degrees exceeding 50.
2. Ultralight. The density of this type is in the range from 0.781 to 0.820 g/cm3. AR degrees are 41.1 - 50.0.
3. Easy. It has a density in the range of 0.821 - 0.870 g/cm3. Her API degrees are 31.1 - 41.0.
4. Average oil. Its density is 0.871 - 0.920 g/cm3, and API degrees are 22.3 - 31.0
5. Heavy oil. Density ranges from 0.921 to 1.000 g/cm3. Degrees API - 10.0 - 22.2.
6. Extra-heavy oil has a density exceeding 1,000 g/cm3. It is also distinguished by its viscosity, which is less than 10,000 mPa*s.
7. natural bitumen. Density more than 1,000 g/cm3. Viscosity more than 10,000 mPa*s.

It is worth noting that the API degrees of the last two types of oil are less than 10.

Traditionally, light oil is produced. However, as mentioned above, its reserves are gradually depleted, and in this case, it is replaced by heavier oil or highly viscous oil.

Thus, heavy oil is oil that has a very high density and also has physical properties that do not allow it to be delivered from the bowels of the earth to the surface using traditional methods. When talking about heavy (high-viscosity) oil, as a rule, all oil having a density above 0.920 g/cm3 is meant, along with natural bitumens.

All heavy oils and natural bitumens are distinguished by the presence in their composition of a fairly large amount of resinous-asphalt substances, as well as nitrogen-containing, chlorine-containing, oxygen-containing, sulfur-containing compounds and metals.

High-viscosity oil deposits are usually located at the intersections of geological basins. Such oil is formed from light oil as a result of the destruction of its low molecular weight components by bacteria, as well as by leaching with water and evaporation.

According to some data, today the earth's interior contains reserves of highly viscous oil, which are several times greater than the reserves of light oil. According to data provided by the World Resources Institute, the largest deposits of high-viscosity oil are located in Canada and Venezuela.

It is worth noting that due to the physical properties of such oil, its production, transportation and processing poses a lot of difficulties. Heavy oil cannot be extracted using the same methods used to extract light oil. To do this, various other methods are used, primarily associated with a decrease in the density of the mineral. After all, more liquid oil moves much more easily through the pipeline.

Heavy oil can be liquefied in the following ways:

1. By adding hydrocarbons or lighter oil to highly viscous oil. Undoubtedly, this significantly facilitates both the oil itself and its fluidity, and, accordingly, the extraction process. However, this method has two big drawbacks. The first is the additional costs, and the second is the lack of constant availability of light petroleum fractions.
2. By heating the pipeline through which oil reaches the surface. To implement this method, the pipeline along its entire length is equipped with special equipment. The disadvantage of this method is a rather large loss of oil during production (up to 20%). This is due to the fact that this part of the oil is used to operate the heating equipment installed along the pipeline.
3. By mixing water and emulsifiers into the oil in order to obtain a fluid water emulsion. However, this method is rational only if an emulsifier of low cost is used, which at the same time is capable of forming stable emulsions. If the oil content in the formed emulsion does not exceed 50%, then the method is considered irrational, since the energy costs during its extraction increase exactly by half. Sulfate or carboxylated ethoxylates can be used as emulsifiers. However, they are distinguished by their high cost, as well as their scarcity, which, in turn, affects the cost of oil produced in this way upwards.
4. By mixing an aqueous solution of a dispersant into heavy oil, as a result of which emulsifying compounds are formed, consisting of ethoxylated alkylphenols. The essence of this method is to inject the solution into the well, where it is combined with oil, which lies at a depth much greater than the location of the pumping pump. The operation of the pump creates oscillations that promote the mixing of oil with the disperser, as well as the supply of oil through the pipeline to the daylight surface. It should be noted that mixing is in no way affected by the size and hardness of the particles that make up the oil product.
5. By supplying diluent to the bottomhole formation area. However, this method is also expensive, since the injection of the diluent must be repeated periodically. However, if the diluent is weighted, then during injection it penetrates to a depth that is significantly below the pump level. Thus, the weighted diluent displaces oil as a lighter product. This thinner contains calcium chloride water, a mixture of two surfactants, and alkali metal hydroxide. The method is characterized by improved operation of deep-well pumps, an increase in the oil feed rate, and a decrease in pressure at the wellhead. In addition, its use does not require the use of additional equipment.
6. In-situ combustion. This method is fundamentally new. Its essence lies in the use of energy that is generated as a result of the combustion of raw materials directly in the formation during the injection of air space into it. It is used both for the extraction of high-viscosity oil and for the extraction of light oil. It is worth saying that the method has already been used several times in some fields and has proven itself very successfully.

For the production of high-viscosity oil by the last method, it is necessary to let air into the well, thereby provoking an oxidative process with an increase in temperature. Due to this, water evaporates, which, turning into steam, forms an oil shaft. It is this that displaces the resulting gases along with oil out through the pipe.

There are three types of in-situ combustion: dry, wet and super-wet. Wet combustion is the most popular because it promotes the combustion front, reduces air consumption, and also reduces the concentration of oil that is burned in the reservoir.

Thus, it is worth saying that despite the additional costs, the production of high-viscosity oil in some regions is gaining popularity. At the same time, a lot of attention is paid to the methods by which it is possible to increase the recovery of hard-to-recover reserves.