Wave technologies for intensifying oil and gas extraction for fields at a late stage of development

. One of the promising areas of research in the field of increasing oil recovery from reservoirs is the study of the influence of elastic vibrations on the productive reservoir. Research on the influence of elastic vibrations on stagnant oil zones in an oil reservoir in order to increase the oil recovery factor is at an early stage. The purpose of this work is to evaluate the effectiveness of using one of the wave methods to increase oil recovery. theoretical and experimental studies of the influence of elastic vibrations on changes in the parameters of the bottomhole zones of the formation and, as a consequence, increasing the productivity of oil wells and the oil recovery factor in oil fields. The work will analyze the wave method of influencing reservoir systems, such as acoustic, and evaluate the effectiveness of this method on changing the characteristics of the reservoir system. The work will conduct various studies on the practical application of wave methods. The effect of the wave method on the components and viscosity of heavy crude oil will also be studied. The proposed wave action creates the opportunity to exploit fields at later stages of development, which are characterized by a high content of asphaltenes, resins and paraffins. The results of the wave impact confirmed the effectiveness of this technology, which made it possible to double the turnaround time.


Introduction
The use of new technologies is very important in the production and development of heavy oil fields.In connection with the increase in heavy oil production, the problem of oil resistance to the precipitation of heavy fractions, consisting mainly of resins, asphaltenes and paraffins, is becoming increasingly urgent and requires further improvement of methods for solving it [1].
In recent years, there has been an increasing interest among oil and gas industry specialists in the practical use of new highly efficient and cost-effective technologies that ensure a stable increase in oil production in difficult geological and industrial conditions.During the development of oil fields, reservoir pressure decreases and at a certain stage of field development, the existing reservoir energy becomes insufficient to displace oil from low-permeability zones of the reservoir into production wells, as a result of which stagnant (slowly moving) oil zones appear in the reservoir.In formations with heterogeneous permeability, in the process of displacement of oil by water, conditions are created for blocking oil in less permeable zones of the formation and, accordingly, an increase in the flow of water to production wells, which leads to a decrease in oil recovery from the formations [2].
One of the promising areas of research in the field of increasing oil recovery from reservoirs is the study of the influence of elastic vibrations on the productive reservoir.
The main part of the theoretical and experimental studies described in the literature concerns the study of the influence of elastic vibrations on the porous medium of the nearwellbore zone of the formation.

Materials and methods
The essence of wave methods for increasing oil recovery from reservoirs is to form to increase the volume of hydrocarbons extracted from the subsoil and reduce energy costs.Using acoustic methods, it is possible to influence mainly only the bottomhole zone of the well.The radius of action of sound, shock waves and pressure waves is much larger and is on the order of tens and hundreds of meters from the well [3].
Let us consider the main phenomena that arise in the process of acoustic exposure.One of the effects that was observed experimentally in an acoustic field with an intensity of 8-100 kW/m 2 is a change in the viscosity of free oil [4].
The decrease in viscosity reaches 20-30% and is explained by the destruction of cyclic structures due to intense oscillatory processes, as well as heating of the oil and the paraffins it contains, caused by the dissipation of acoustic energy [5].
In addition, when acoustic waves propagate in a saturated porous medium, its effective thermal conductivity increases.Thus, heating in an acoustic field with an intensity of more than 1 kW/m 2 and a frequency of 20-1500 kHz leads to an increase in temperature away from the heater compared to conventional heating by 7-10°C, and the rate and radius of heating increase [4].
Calculations performed for a longitudinal wave propagating in an oil-saturated porous medium with permeability values typical for reservoirs show that at current acoustic field intensities, acoustic flows cannot have a decisive influence on the productivity or injectivity of reservoirs.
Acoustic cavitation of a liquid at a pressure exceeding the saturation pressure is associated with the presence of nucleating gas bubbles in it [6].Pulsations of bubble walls can lead to their growth as a result of so-called rectified diffusion.Bubbles that have reached a certain maximum size collapse, which leads to the appearance of shock waves that promote mixing of the liquid and cleaning of pores, and in some cases, to a slight increase in porosity due to the destruction of the matrix.It has been established, however, that the phenomenon of rectified diffusion and, accordingly, cavitation occurs when the acoustic pressure reaches a certain threshold value.For free liquids at a pressure above the saturation pressure, this threshold reaches tens and hundreds of atmospheres and is practically unattainable in real conditions [3].

Results and Discussion
Thus, it has been theoretically and experimentally proven that the use of pulse-wave technology for influencing productive formations allows, in the process of well treatment, to solve a number of hydrodynamic problems in determining filtration parameters and E3S Web of Conferences 463, 03007 (2023) EESTE2023 https://doi.org/10.1051/e3sconf/202346303007anisotropy of the formation, operational monitoring of the oil-water contact and identifying layered heterogeneity.
Power ultrasound, as an emerging green technology, is attracting increasing attention from the oil industry.The physical and chemical effects of periodic vibration and the explosion of acoustic cavitation bubbles can be used to perform a variety of functions.The mechanisms and effects of acoustic cavitation are presented here.In addition, applications of high-power ultrasound in the petroleum industry are discussed in detail, including enhanced oil recovery, oil sands recovery, demulsification, viscosity reduction, and treatment of oily wastewater and oil sludge.From the perspective of industrial background, the key problem and solution mechanism, current applications and future development of high power ultrasound are discussed [7].

Impact of emitters on liquids
During operation of the emitter, along with the generation of sound waves, cavitation phenomena are also observed.
A sharp decrease in pressure in a liquid, leading to cavitation, can be caused either by purely hydrodynamic effects due, for example, to Bernoulli's law (the so-called hydrodynamic cavitation), or due to sound waves (acoustic cavitation).
During hydrodynamic cavitation, vapor-gas bubbles can reach large sizes (centimeters or more).Acoustic cavitation is characterized by very small sizes of emerging bubbles (10-3 10-2 cm).These bubbles are unstable [8].Depending on the pressure difference between the bubble and the liquid, they grow, pulsate or collapse.As the bubble collapses, the pressure at its center increases.As a result, a spherical shock wave forms and propagates in the liquid in the direction from the center of the collapsed bubble.Compression of the bubble, in addition, leads to a sharp increase in the temperature inside the bubble.The pressure and temperature arising during the collapse of a bubble can reach, respectively, hundreds of MPa and thousands of oK [25][26].Moreover, the moment of liquid rupture when a cavitation bubble appears is accompanied by the appearance of an electric field with a intensity of ~ 105 V/m [9].
From the above it follows that emulsification of the dispersed phase with a vibrator will occur in two stages.Initially, as a result of the instability of interphase waves, rather large drops or particles are formed, which in the second stage are crushed by shock waves that arise during the collapse of cavitation bubbles [10].

Sound-chemical reactions in water and aqueous solutions
The effect of sound on a liquid [8][9] leads to the excitation of water molecules: And further to the ionization of these molecules1): Chemically active gases -O2, H2 and N2, dissolved in the sonicated solution, have a dual effect on sonic chemical reactions.Firstly, O2 and H2 are involved in radical transformation reactions: Where hydroperoxide radicals recombine to produce hydrogen peroxide: And the interaction of H• radicals leads to the formation of molecular hydrogen: Nitrogen participates in gas sonochemical reactions, the end result of which is nitrogen fixation: Звук N H NH +→ (6) 1) Here and below, the molecular excitation sign (*) is omitted; (•) -radical sign.Recombination reactions involving N atoms can be very diverse and complex.N atoms most likely react with OH• radicals in the following way: Nitric oxide NO does not react with water.
The main products of the recombination of nitrogen atoms with hydroxyl radicals are HNO2, formed by reaction (12), and HNO3, which is obtained together with HNO2 from NO2: At the same time, as the experiment shows, the ratio of the concentrations of nitrous and nitric acids -    In addition, chemically active gases, penetrating into the cavitation cavity, participate in the transfer of electronic excitation energy to water molecules, and also, possibly, in charge exchange processes.
Paper [11] presents the results of a study of a terrigenous core sample.A sample with a porosity of 23.7% and a permeability of 0.6 D was studied.Based on X-ray E3S Web of Conferences 463, 03007 (2023) EESTE2023 https://doi.org/10.1051/e3sconf/202346303007microtomography of the core, a digital 3D model of the porous sample was created [12].Numerical modeling of fluid flow in the pore space with superimposed pressure fluctuations (simulation of acoustic effects) made it possible to identify the features of the hydrodynamics of the flow (Figure 1).Fig. 1.Distribution of steady flow velocities in the cross section of the pore space [11].
It was found that superimposed oscillations lead to the emergence of an additional directed flow with characteristics depending on the parameters of the superimposed oscillations.In other words, during acoustic exposure there is an "extra charge" to the permeability value measured for stationary conditions.
Software simulation was also conducted by Mohammed and Mahmoud [14] to compare the experimental results with the software results and validate the results of their experiment.
Numerical modeling was carried out using the finite element method.The Darcy flow model combined with acoustic pressure in COMSOL multiphysics was used to estimate the pressure and temperature distribution in the target environment when exposed to ultrasonic waves.Figures 2 and 3 show the distribution of pressure and temperature, respectively.Fig. 2. Pressure distribution in the oil reservoir model [14].
In [15], the effect of ultrasound on reducing the viscosity of super-heavy oil was studied.The initial viscosity of super-heavy oil was 1250 MPa•s.The wave frequency range is from 18 kHz to 25 kHz and the power outputs are 100 W -1000 W. Ultrasound at frequencies of 18, 20 and 25 kHz reduced oil viscosity to 480, 890 and 920 MPa•s, respectively, although irradiation time affected these changes.The results also showed that cavitation caused by ultrasonic radiation can break down large heavy molecules of extra-heavy oil into light hydrocarbon substances.In addition, it was concluded that the main significant parameters for reducing the viscosity of heavy oil are ultrasonic frequency, radiation power and time.This conclusion is consistent with studies [16] on the influence of ultrasound power and frequency on the mobilization of oil in porous media.They tested a range of frequencies and powers of ultrasonic waves and concluded that the recovery rate was consistent with the frequency and power of ultrasound.

Method for assessing the influence of wave action on the pore-liquid-gas system of the formation
Elastic waves propagating in any medium experience absorption due to viscosity (internal friction forces), thermal conductivity, and at high frequencies, molecular absorption in the medium.In this case, the energy of sound waves turns into thermal energy.In addition to absorption, sound energy is scattered by elastic inhomogeneities in the medium, and the scattering of sound increases significantly when the size of the inhomogeneities is comparable to the length of the sound wave.
Absorption of elastic vibrations Assessment of changes in signal amplitude during the propagation of acoustic waves through the formation and in the formation mass in the following form: Where Ax is the amplitude of the acoustic wave at a distance x from the vibration source; Ax1 -amplitude of the oscillation source; x -distance from the source of vibrations to the point at which the amplitude is determined in m; α is the attenuation coefficient of acoustic radiation in the medium; n is the exponent, n = 0 for a plane wave, n = 0.5 for a cylindrical wave and n = 1 for a spherical wave.

Methodology for calculating the viscosity estimate
The dependence of dynamic viscosity on the vibration amplitude is determined expression (2), which is transformed to the following form if we substitute the acoustic pressure formula (Figures 3-7):  Where µ0 is the viscosity of oil before acoustic impact, P0 is the amplitude of oscillations; α -attenuation coefficient.The viscosity of oil under direct influence of vibrations decreases significantly and remains at this level, again at low frequencies.It is also clear from the graph that it takes on its original value only when moving away from the well to very large distances of several hundred meters.
In addition, when acoustic waves propagate in a saturated porous medium, its effective thermal conductivity increases.From my calculations, the process of propagation of acoustic waves was studied, and based on the results obtained, a diagram was created showing the propagation of these waves in a porous medium (Figure 7).
The mechanism for the propagation of elastic vibrations in the formation is formed by the emitter, which creates these waves from all sides around the well.Under the power of ultrasonic waves, bubbles are formed in the liquid, which have two stages: expansion and collapse.The collapse of the bubbles causes high energy in the medium.

Methodology for assessing well productivity
Darcy's law shows the linear relationship between the volumetric flow rate of a liquid or gas and the pressure drop in porous media.This law has a very wide scope of application in hydrocarbon production and is considered the basic law of filtration of liquids and gases.Darcy's law is empirical; it shows how pore fluid moves under relatively small pressure gradients.It also shows the nature of the movement when water is filtered through the soil under various hydraulic structures, through the walls and bottom of canals.This law is needed to calculate productivity in oil and gas production.
Where v is the fluid filtration rate m 3 /s; Q -volumetric flow rate of fluids in m 3 /day; F is the area of the porous medium under consideration; k -permeability coefficient µm 2 ; µdynamic viscosity of fluids MPa.s; ΔP -pressure drop over length L.
From the results obtained, we can conclude that for deep impact on the formation, the emitters must be low-frequency, since as the frequency increases, the oscillation amplitude very quickly decreases exponentially, which we have already seen in the graph of the dependence of acoustic pressure on frequency and distance (Figure 8).Based on the foregoing, we can draw the following conclusion: when wave action is applied to an oil well at frequencies less than 5 kHz, the average is 35%; for higher frequencies up to 15 kHz, the productivity increase drops to 4%.For deep impact on the productive formation at distances of hundreds of meters, the emitters of elastic vibrations must be quite low-frequency.The frequency of such emitters should be on the order of several kHz.

Conclusion
Thus, one of the most important physical methods for increasing oil recovery was considered.
E3S Web of Conferences 463, 03007 (2023) EESTE2023 https://doi.org/10.1051/e3sconf/202346303007Ultrasonic waves influence productive formations to solve a number of problems in oil production and increase oil recovery: reducing oil viscosity, reducing residual oil saturation, improving permeability and preventing the formation of deposits.
Based on the above research results and mathematical modeling, it can be noted that the combination of periodic ultrasonication, low frequency and short distance from the energy source gives the best oil recovery factor.More reliable results can be obtained by testing carried out in reservoir conditions.This technology is among the methods of reservoir stimulation.Their effectiveness is determined by the need to achieve the following goals: • Economic and technological efficiency of the impact.
• ˗Safety and cleanliness of the environment.
• Compatibility in terms of technological features and technical implementation of the application with existing methods of influencing the formation.
In order to increase the total and current oil production, the injectivity of injection wells and the flow rates of production wells, it is necessary to conduct a number of theoretical, laboratory and industrial studies, to correctly select one or another method of treating the bottomhole formation zone, which will significantly increase the oil recovery factor.

Fig. 7 .
Fig. 7. Scheme of propagation of acoustic waves in a porous medium.

Fig. 8 .
Fig. 8. Graph forecasting the dependence of well flow rate before and after ultrasound.