The Effect of Ultrasonic Waves on Crude Oil Recovery

Abstract

In recent years, ultrasonic technology has played an important role in the development of oil fields, which has improved oil recovery. Ultrasonic waves are a very suitable method for producing oil at a low cost and without environmental pollution. The reservoir is treated using high-power sonication, which affects the physical properties of the oil and thus improves the permeability, which increases the oil recovery. The ultrasonic technique is also used to reduce the damage of the formation in the areas near the well, and this reduces the penetration of mud and sediments. However, ultrasonic waves remove oil barriers to the well and improve oil recovery for a long time. In this chapter, recent developments and laboratory and field results of ultrasonic waves in improving oil recovery will be discussed, and it will be shown that these waves are highly efficient.

1. Introduction

In the world, energy is the main condition for the development of human society. Oil, gas, and coal are the main sources of energy that have led to the development of human civilization in recent years [1]. Given that the demand for energy from these energy systems and the severe problems and challenges in the oil and gas industry are increasing day by day, the oil production capacity cannot meet this volume of demand. Also, because oil prices are high in the world, it has affected the oil market and the structure of international cooperation in this industry [1, 2]. However, the continuous reduction of hydrocarbons is an undeniable issue and serious efforts should be made to solve its problems [3]. Reduction in production can occur for two reasons: 1) reduction in reservoir pressure and 2) formation damage. Sedimentation of asphaltene and wax on rocks can occur due to the flow of drilling fluids, which is called formation damage. Damage formation is one of the main reasons for reducing the productivity of oil wells and has adverse effects on well production. Various techniques have been performed to eliminate formation damage. These techniques include high-pressure fractures and acid and solvent injections, which often have many disadvantages, including high cost, extensive facilities, and environmental problems [4, 5]. New and effective technologies have been developed to solve the mentioned problems in the oil industry. Ultrasonic oil recovery technology is one of the most effective solutions developed in the USA in the 1950s [6]. The ultrasonic technique and the use of its waves have desirable advantages such as low pollution, cheap, high efficiency, and environmentally friendly. Impurities and sediments in oil exploitation reduce oil flow and thus reduce production [7]. For this purpose, high-power ultrasonic waves are used to increase the oil permeability, which destroys the oil layer particles and increases the permeability by creating high sound acceleration [8]. Oil recovery technology means that the sonication operation leads to a change in the physical properties of the fluid, which improves the fluid flow status [1, 2] and reduces the pressure gradient of the porous medium [9].

In this chapter, the aim is to review recent developments in ultrasonic oil recovery technology, as well as the effect of these waves on the physical properties of the fluid and the viscosity of the oil.

2. Advantages of ultrasonic oil recovery technology

Due to the problems mentioned in the oil industry, the ultrasonic method is one of the suitable options for oil recovery. Oil recovery has the following advantages [7]:

• When using ultrasonic waves in areas of oil wells, it does not cause any pollution to the environment.

• The sonication operation is a simple and easy operation and has no complexity.

• The use of ultrasonic waves can be combined with other methods such as sonic water injection and acoustic acidification and increase the recovery of crude oil.

• The equipment used in crude oil recovery by ultrasonic waves is installed on vehicles and has a wide application, cheap, and high efficiency.

This equipment is shown in detail in Figure 1.

Figure 1.

The schematic of ultrasonic oil recovery device.

3. Effects of sonication operation

3.1 Mechanical vibration

Ultrasonic waves have a series of mechanical effects that change the velocity of elastic particles and cause agitation, loosening, scattering, and degassing. Mechanical vibrations also cause loss of cohesion between blocked particles, resizing capillary pores and reducing surface tension. These vibrations also cause very small cracks in the rocks of the formation and cause the separation of crude oil from the rocks. Impact pressure from high-frequency, high-power ultrasonic waves accelerates large molecules such as wax, asphaltene, and colloids, breaking the chain of molecules due to inertia [10, 11, 12, 13, 14, 15, 16].

3.2 Cavitation

The process of growth and collapse of hollow fluid bubbles due to sonication operations and changes in sound pressure is called cavitation. Pressures above 105 MPa can cause cavities to collapse [17]. This high pressure also causes secondary effects such as luminescence, phonation, ionization, and chemical reactions. One of the obstacles to oil flow is gas resistance. Gas resistance refers to a large number of gas cores. These gas nuclei combine to form larger bubbles, approaching the dredging target [18]. Frequent cavitation explosions occur in the fractures of the formation and on the solid surface, leading to high pressures and the consequent explosion of particles adhering to the surface. Also, due to the transverse flows of liquids and their alternating currents, particles are quickly removed from the surface [10]. However, cavitation breaks the molecular bonds of crude oil and reduces the molecular mass. Reducing the molecular mass reduces the viscosity and thus improves the fluidity of the crude oil.

3.3 Thermal action

The internal friction of crude oil is the reason for the resistance of the oil flow. As the viscosity of the oil decreases, the oil concentration also decreases, leading to improved flow. Therefore, to improve the flow of crude oil, its viscosity can be reduced, and this is possible by increasing the temperature. By absorbing ultrasonic waves, acoustic energy is converted into thermal energy, and also the boundary friction at the interface increases the temperature of the crude oil. However, at the moment of bubble collapse, a large amount of heat energy is released by cavitation, and with increasing ultrasonic frequency, the absorption of waves and boundary friction becomes more intense. Eventually, with increasing sonication power, cavitation and thermal energy become more significant [19, 20, 21, 22, 23].

4. Recent developments in sonication operations to improve oil recovery

In recent years, various devices have been invented that can improve the recovery of crude oil by ultrasonic waves. One type of environmentally friendly viscosity reduction is shown in Figure 2 [24, 25]. This device has a very good anti-wax and antifouling feature and is used for underground oil pumping. This device can be used to increase the flow of crude oil, which increases pump efficiency and production. This device is also suitable for wells containing different wax and water and has good safety and no pollution.

Figure 2.

The structure of a kind of environmentally friendly, anti-wax, and antiscaling viscosity reduction device [24, 25].

One of the problems of the oil industry is the elimination of the scale of pipelines, and to solve this problem, an electromagnetic ultrasonic antifouling device was invented [26, 27]. The schematic of this device is shown in Figure 3 [25].

Figure 3.

The structure of electromagnetic ultrasonic antiscaling device [25].

Using an ultra-strong alternating magnetic field and ultrasonic sound field, the device affects the physical morphology and chemical properties of the crude oil sediments, dispersing and loosening the sediments completely and not adhering easily to the pipe wall. Also, with the invention of this device, they achieved many advantages, which are good antifouling effect, long life, no pollution, comfortable maintenance, and environmentally friendly [26].

Due to the fact that the viscosity reducing device cannot be used for more than 25% wax content, to solve this problem, a double sonic eddy current anti-wax viscosity reduction device was invented [28]. The schematic of this device is shown in Figure 4 [25]. This device has useful capabilities, and a two-stage ultrasonic oscillator is used to improve the sound frequency and can destroy paraffin wax crystals and lead to a great reduction in viscosity. In addition, the use of eddy currents increases the fluidity of crude oil, prevents wax deposition, and increases oil flow capacity. In the oil industry, this device can be used for vertical, sloping, and horizontal oil production wells [28]. However, to improve the transmission efficiency of all oil production systems, three special types of cables are used, which are shown in Figure 5 [25, 29].

Figure 4.

The structure of double sonic eddy current anti-wax viscosity reduction device [25].

Figure 5.

Three kinds of special cables for improving transmission efficiency of the whole oil production system [25, 29].

4.1 The effect of different ultrasonic parameters on viscosity and oil recovery efficiency

Recently, important studies and results have been obtained in the field of improving the recovery of crude oil using ultrasonic waves. Various ultrasonic parameters can have a significant impact on improving crude oil recovery. These parameters include cavitation, temperature, time, power, and frequency. Each of these parameters has a significant effect on crude oil recovery, which must be optimized for each specific operating condition of these parameters in order to achieve maximum recovery. In this section, the explanation and effect of these parameters are discussed.

4.1.1 The effect of ultrasonic temperature and cavitation

In a previous study, an ultrasound cleaning tank was used to separate oil from sludge [30]. Ultrasonic waves can separate solid particles from crude oil [31]. The results were obtained after deoiling the oil sludge, and the oil content increases when the temperature is above 40°C. However, too high temperature weakens cavitation and delays the separation of solid particles from crude oil [32]. That is, from the temperature range of 30 to 40°C, the cavitation intensity increases and reaches its maximum value at 40°C, and then with increasing temperature from 40 to 60°C, the cavitation intensity decreases and reaches a constant rate [30]. As a result, it can be said that cavitation has a maximum value at low temperature (40°C), and high temperature (>40°C) is suitable for molecular motion and increases the number of cavitation nuclei [30]. Also, the oil content increases in the range of acoustic pressure above 0.10 MPa because cavitation increases with increasing acoustic pressure [33]. Temperature, power, and frequency parameters of 40° C, 0.1 MPa, and 25 kHz, respectively, can increase the oil recovery rate by 55.6% [30]. The optimal conditions for these parameters must be determined. The optimum conditions for oil sludge treatment for frequency, intensity, power, and soil-to-water ratio are 25 kHz, 0.33 W/Cm², 300 W, and 1/2, respectively [34]. With increasing temperature, the viscosity of the crude oil and the adhesion stress between the oil and the sand decrease. There is also a positive correlation between cavitation nuclei and sonication temperature. That is, the higher the temperature, the greater the number of cavitation nuclei. However, with a large increase in temperature, the internal pressure of the cavitation bubbles increases, which reduces the intensity of cavitation [35, 36].

With the radiation of ultrasonic waves, cavities are created in which large bubbles are created due to heat, and these waves cause these bubbles to collapse. The mechanical effect of this collapse causes the suspended conglomerates to disintegrate [37]. The increase in temperature and ultrasonic cavitation leads to the production of hydromechanical shear forces and causes disruption in macromolecules. These collapses that occur in the bubbles cause the creation of shear shock waves and solvent microjets that create turbulence in the surface layer around the solid particles and cause high local temperatures [38].

4.1.2 The effect of ultrasonic power

High ultrasonic power is one of the main features of ultrasound in crude oil recovery. Following recent research, an ultrasonic reactor was used to purify petroleum sludge [39]. The ultrasonic reactor was able to increase the oil recovery efficiency above 90% for some samples with a power of 240 W. Given that oil recovery increases with increasing power, the further increase of ultrasonic power not only does not improve oil recovery but also leads to reduced efficiency [39]. With a further increase in power, the ultrasonic recovery does not increase. It can be concluded that the cavitation phenomenon is responsible for the excretion of adsorbed molecules, and the effect of this phenomenon is affected by the size of the bubbles because larger bubbles can store more energy [35, 40, 41]. Ultrasonic cavitation is effective in inhibiting the growth of wax crystals. Ultrasonic cavitation causes long-chain alkanes to be converted to short-chain alkanes and C∙C bonds are broken [42]. Also, after the irradiation of ultrasonic waves, the content of long-chain alkanes (C₁₆–C₂₂) decreases and short-chain alkanes (C₉ and C₁₀) are created [43]. With the increase of light hydrocarbons, wax solubility improves and the freezing point of crude oil decreases.

However, an optimal value for ultrasonic power must be determined, and increasing the power from a certain threshold does not help to improve oil recovery [35]. Very high levels of ultrasonic power can produce a lot of acoustic energy, and the energy is converted to smaller temperatures and pressures by small bubbles, and microscopic turbulence breaks the bonds and the adsorbed molecules are expelled [44]. Also, further increase of ultrasonic power due to inhibition of cavitation microbubble size cannot improve oil recovery [39]. However, ultrasonic power can be used to increase oil recovery, and the frequency parameter must be increased to increase recovery speed [39].

4.1.3 The effect of ultrasonic time

The combined method of ultrasound and thermochemical cleaning treatment for oily sludge was also investigated in another previous study [35]. After the operation, oil layers were collected for analysis. After 15 minutes of testing, the oil recovery is 99.28% and remains constant with a further increase in recovery time. Initially, under ultrasonic radiation, oil is desorbed from the surface of the sand and an oil–water emulsion is formed at a low concentration. At the beginning of the operation, the desorption rate is high, which leads to an increase in oil recovery. However, as the oil–water emulsion concentration increases, the oil re-adsorption on the removed sand surfaces increases at the same time. Also, when the desorption rate is equal to the re-adsorption, a further increase in sonication time does not increase oil recovery [35, 45]. As the ultrasonic radiation time increases, the bubbles inside the crude oil reach a critical size and then collapse. As the bubbles increase in size and collapse, the volume of crude oil increases, leading to a decrease in viscosity [37].

4.1.4 The effect of ultrasonic frequency

Another feature of ultrasound to increase crude oil recovery is low frequency (10–35 kHz). Reducing the frequency both increases cavitation and decreases the attenuation of acoustic energy [20]. However, the lower the frequency, the easier cavitation will occur [35]. Also, two types of 28 and 40 kHz generators were examined, and according to the results, ultrasound with a frequency of 28 kHz does better than 48 kHz and this is because [30]:

1. The 28-kHz frequency performs better in washing solid particles and the cavitation threshold at the 28-kHz frequency is less than 48 kHz, so the cavitation intensity is higher at 28 kHz and therefore the separation efficiency is higher at 28 kHz.

2. Koyusov research has shown that the optimal frequency for coagulation of solid particles is 21–25 kHz, and with increasing ultrasound frequency, the number of cavitations increases and causes strong vibrations.

Also, sonication operation has a significant effect on the viscosity of crude oil, which increases the fluidity, flow, and recovery of oil. In a study on a type of crude oil with a viscosity of 1250 MPa.s, wide ranges of frequencies from 18 to 25 kHz and power from 100 to 1000 W were investigated [46]. Ultrasonic frequencies of 18, 20, and 25 kHz can reduce the viscosity of oil by 480, 890, and 920 MPa.s, respectively [46]. Therefore, cavitation created by ultrasonic waves is able to break down heavy oil molecules into lighter hydrocarbons, and the power and irradiation time of the waves are the main parameters for reducing viscosity [46]. Another sample of crude oil with n-alkanes and tar-asphaltene compounds was examined at a resonant frequency of 24.3 kHz and a generator power of 4000 W [47]. Results were reported on the effect of ultrasonic waves on the viscosity of paraffin oils, and it was shown that these waves lead to a decrease in viscosity and pour point [47]. These results are also consistent with reports in other reports [48, 49] of reduced viscosity due to ultrasonic radiation. In another study, the rheological behavior of crude oil irradiated with ultrasonic waves was investigated [50]. Dissolution of heavy compounds in crude oil can be achieved by irradiation of ultrasonic waves with a frequency of 45 kHz and an optimal time of 45 minutes. In a recent study, we also found that the three parameters of time, power, and ultrasonic frequency have a significant effect on oil viscosity [51]. A sample of crude oil in oil reservoirs, named as Bangestan, at the Marun field, located in the south of Iran was employed for experiments. Brookfield dvz-lll ultra Rheometer was used to measure viscosity. The schematic of the equipment used is shown in Figure 6 [51]. To produce ultrasonic waves of bath type, two ultrasonic generators were used, the first generator (YAXUN YX2000) with a frequency of 42 kHz and power of 35 and 50 W and the second generator (QUIGG SR 2014.16) with a frequency of 46 kHz and output power of 50 W. Simultaneous thermogravimetric and differential thermal analyzer (TGA/DTA Netzssh STA 409 PC LUXX) have been used to investigate the effect of ultrasonic waves on crude oil mass and thermal behavior. Crude oil viscosity was irradiated with ultrasonic waves at different times, frequencies, and power of sonication in ambient conditions, and its viscosity was measured after cooling of crude oil [51, 52]. As shown in Figure 7 [51], the effects of three parameters of time, frequency, and ultrasonic power on the viscosity of crude oil are significant. The sonication time has the greatest effect on the viscosity and with increasing the radiation time, the viscosity decreases sharply. On the other hand, the other two parameters have little effect on the viscosity of crude oil [51]. Good results in this field can be achieved by using appropriate statistical methods, modeling and artificial intelligence [53, 54, 55, 56, 57, 58, 59].

Figure 6.

Schematic of equipment used for investigating the effects of ultrasonic waves on the viscosity and thermal properties of crude oil [51].

Figure 7.

The effect of triple ultrasonic factors on the viscosity of crude oil [51].

4.2 Mechanism of action of ultrasonic waves

In this section, the changes of molecular bonds of heavy crude oil due to ultrasonic radiation are analyzed. An example of a Fourier transform infrared spectroscopy (FTIR) spectrum of a sample of heavy crude oil is given in this section to investigate the effect of ultrasonic waves on the molecular bonds of crude oil (Figure 8) [60]. As can be seen in Figure 8 [60], the angular vibrations of methyl and methylene are present in the wavelengths of 1378 and 1458 cm⁻¹, respectively. A carbon–carbon double bond is observed at wavelength of 1599 cm⁻¹ and the tensile vibration of methylene at about 2854 cm⁻¹ and for methyl at 2952 cm⁻¹. However, when heavy oil is exposed to ultrasonic radiation for 6 minutes, the peak intensity increases, indicating an increase in methyl functional groups. Also, the chains of heavy compounds are broken, leading to a decrease in viscosity. But, an increase in the time of ultrasonic radiation (12 min) reduces the intensity of the peaks. This means that due to the longer irradiation time, more long-chain molecules are converted to short-chain molecules, but due to excessive temperature and crossing the temperature threshold, light compounds evaporate and ultimately increase viscosity.

Figure 8.

FTIR spectra [60].

Severe cavitation can occur due to the intensity of ultrasonic radiation in heavy oil. In general, it can be said that acoustic cavitation has three main effects: mechanical, chemical, and thermal. Each of these three factors has a specific effect on oil. Thus, the mechanical agent creates a strong stirring effect and the thermal agent creates a high-temperature and high-pressure effect in the fluid. As mentioned, the contents of the functional groups increase as a result of sonication operations, which indicates that the molecular chains are broken and the heavy components of the oil are decomposed into lighter components. Reduction of heavy components and breaking of long chains due to wave radiation lead to a decrease in viscosity, which can be due to acoustic cavitation. Therefore, to better understand this issue, the carbon number distribution of three samples of heavy oil is given in Figure 9 [60]. As the radiation time increases, the total amount of carbon, called long chains, gradually decreases. As shown in Figure 9 [60], there are carbon chains of C₄₀ and above C₂₀ in heavy oil. As the ultrasonic radiation time increases, these chains are broken and the amount of carbon is reduced. This trend occurs in two other heavy oil samples, but in C₁₁–C₂₀ carbon the number of light carbon chains decreases with increasing time. This is for the same reason as mentioned in the previous section, that as time increases, they produce excessive temperature waves that cause lighter compounds to evaporate and viscosity to increase.

Figure 9.

Results of carbon number distribution [60].

5. Future views

Considering many studies have been performed on the effect of different ultrasonic parameters on increasing crude oil recovery, the ultrasonic cycle parameter has not been studied in all studies. It seems that different ultrasonic cycles can help a lot in improving the recovery of crude oil in the oil industry, in future laboratory and field studies. The ultrasonic cycle section is divided into active and passive intervals. In an ultrasonic homogenizer, the number of cycles is divided from 1 to 10. Each cycle represents a unique amount of active and passive intervals. In all recent studies, the effect of these active and passive intervals has not been investigated, which is a very important parameter in the recovery of crude oil.

6. Summary

This chapter examines recent developments and the effects of ultrasonic waves on viscosity and crude oil recovery. The results show that these waves with three mechanical, chemical, and thermal factors can improve oil recovery and break down heavy compounds and turn them into lighter compounds [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23]. It is important to note that the various ultrasonic parameters (frequency, power, time, cycle, etc.) must be optimized. An optimal value can achieve the desired result. Ultrasonic waves also have great advantages such as cheapness, convenience, and environmental friendliness. It has also been concluded that sonication operations can decompose heavy colloidal compounds of crude oil and break down asphaltene molecules. Given that the presence of asphaltene in oil reservoirs can be problematic and clog pores and increase viscosity, it is important to know information about ultrasound parameters because these waves can be very useful in breaking down heavy molecules and reducing viscosity. In addition to the effect of the mentioned parameters on the recovery of crude oil, the type of these waves is also important. This means that intermittent or continuous use of these waves can have different effects on crude oil recovery [61]. Thus, intermittent sonication operations lead to greater crude oil recovery than continuous sonication [61]. In addition to increasing the permeability of ultrasonic waves [62], the vibrations of these waves can also affect the flow of oil and lead to improved water drive recovery and oil structure changes and viscosity decreases [63, 64]. However, the use of another parameter, the ultrasonic cycle, can be effective and should be researched in the future.

Conflict of interest

The authors declare no conflict of interest.