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increasingly important process in oil-gas fields. Several techniques have demonstrated their capability to recover a substantial amount of oil. This paper discusses the main field and laboratories developments achieved so far with ultrasonic-assisted EOR as well as different electronics and mechanical subcomponents designs of such probes. While enc...
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... same authors suggested the usage of a similar probe to reduce the water cut around the perforation zones in horizontal wells with an online geophysical study of the surrounding zone in one of Western Siberia reservoirs which was characterized by a relatively high water cut [16]. The tool which is 40 mm diameter consists of a stack of 18 KHz magnetoresitive transducers and a special jet pump for horizontal well. It was deployed into one of Samtor oil field well of 102 mm diameter casing using a wireline truck ( Figure 14). The tool is also equipped with a set of sensors to measure online pressure, temperature, natural radiation of the rock, flow of the fluid, magnetic locations of the couplings, soil/water content, and the resistance of the fluid. A dedicated cable was used to deliver up to 5 kW of power to sensors which operated at an average power of 1.5 kW. Figure 15 shows the configuration of the tool while Figure 16 shows the geophysical plots of the well. The existence of a flow of the fluid would correspond to a change of temperature, while the existence of water would correspond to low resistance. Hence, the tool indicated that the zone ranging from 1955 m to 2010.48 m produces mainly water and thus only the zone between 1892 and 1909 m was chosen for ultrasonic treatment and using the jet pump. This has led to a reduction of the water cut from 80 % to 59.3%. In China, an ultrasonic-based EOR device, namely ZYQZ device, which was manufactured by Hanwei Petroleum Machinery Research Institute was used in several oil fields to recover up to 9% of crude oil, as well as to inhibit paraffin deposition [18]. The instrument that consists of a stack of several piezeoelecric sensors (PZT-4) can only operate for relatively short period of time due to the low Currie temperature. More recently, another PZT-5 based ultrasonic sensor that features magnetic orientation was designed and built to deliver a power of up to 100 kW to an array 10-35 kHz ultrasonic probes using a multicore cable that consists of twisted copper wires covered by polythene cover and 30 galvanized steel wire of 1.54 mm diameter (Figure 17). The usage of multicore cable is justified by its high tensile strength as well as its excellent bending resistance, even though its overall length is slightly higher. Figure 18 shows a photograph of the ultrasonic probe that was able to operate at temperatures ranging from -10 to 150 0 C to recover up to 30% of oil. The results have revealed that a long lasting decrease of oil viscosity can be obtained if ultrasonic treatment is combined with chemical agents. 18. An ultrasonic probe used for EOR [18] In addition to field trials, other laboratory tests were also conducted to assess the performance of ultrasonic-assisted EOR under controlled conditions. Hence, in [23], it was demonstrated that CO2 combined with ultrasonic waves leads to higher efficiency. In [24], a laboratory experimental study was conducted on man-made cores of 2.5 cm diameter and 7 cm length, with permeability of 30, 80, and 150 mD respectively to investigate the potential of ultrasonic waves on removing different kind of plugs that may occur in oil reservoirs: drilling fluid plug, paraffin deposition plug, polymer plug, and inorganic scale plugs. It was concluded that ultrasound -chemicals composite plug removal provides a better removal effect than using ultrasonic technique alone, where the recovery increases by up to 30%. A suggested explanation is that chemical agent reduce the adhesion strength of plugs which will enhance the effect of ultrasonic removal. Another interesting research was conducted to investigate the potential of ultrasonic excitation for oil de-emulsification over chemical agents. As shown in Figures 19 and 20, ultrasonic method provides a better de-emulsification. In [27], it was demonstrated experimentally in the lab that EOR recovery with ultrasonic depends on the type of crude oil in the formation: While it can reach up to 20 % increase of recovery in case of light crude oil (crude oil of viscosity around 5.39 cp), it reduces the EOR recovery in case of higher viscos crude oil (crude oil of viscosity around 74 cp). This can be explained by the fact that for the case of high viscos crude oil, ultrasonic radiation cause asphaltene aggregation in a toluene-pentane mixture and consequently the disintegration of asphlatene micelle structures of the oil and its dissolution in the fluid which leads to an increment in the oil viscosity. However, this can be beneficial with CO2- EOR to lower its flow rate in the ...
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... tool, which is encapsulated within an IP67 enclosure consists of a waveguide made of titanium allow BT6 with magnetoresistive transducers to operate at temperature of up to 100 0 C. During the period from 2010 to 2012, more than 100 operations were performed to achieve an average of oil recovery of 4.4 tons per day in Western Siberia and 10.2 tons /day in Samara region. In addition, a decrease of 4% of water cut, and an increase of a bottom pressure by up to 30 bars was obtained in both fields. Figure 7 shows the block diagram of the 10 KW ultrasonic generator which was used at the surface. It consists of three main units: the power supply block unit that is fed to a 3 phase 308 V/50Hz power supply, the control block unit that receives borehole data (i.e. downhole pressure and temperature) to optimize the ultrasonic excitation into the reservoir, and the power block unit. In [15], another 20 KHz ultrasonic tool, namely the CSYY60H10, was suggested ( Figure 8). The tool features a special low-loss, water-proof power cable and a piezoelectric transducer made of lithium neonate crystal that has better piezoelectric properties than common piezoelectric ceramic. Figure 9(a) shows the structure of the ultrasonic transducer. It is made of 36 0 Y-cut lithium niobate (which is the commercial available type of LiNbO3 which is close to the optimal cut of 38.9 0 for thickness displacement. The probe consists of two electrodes: island electrode, which is connected to the signal wire, and ring electrode, which is connected to an aluminum alloy shell. Both electrodes are made of copper and the piezoelectric vibrator is designed based on the theory of air backing. Figure 9(b) shows the three dimensional view of the probe. It consists of several piezeoelectric vibrators placed at different cross sections of the tool in order to produce a coherent wave field which has the advantage to increase the radius of influence. In [16], an ultrasonic-based device was tested in the perforation area of a horizontal well to reduce the amount of water-cut in the produced crude oil downto 20%. In three other horizontal wells located in western Siberia, a sonochemical treatment (e.g. using a combination of ultrasonic and chemical agents) was successfully used to increase the oil production from 23 to 33 tons per day and the same study revealed that the methods leads to a higher efficiency than using ultrasonic alone [17]. In the paper, three 20 KHz ultrasonic equipment of 6 Kw each were suggested to deploy an integrated solution for EOR: two well head equipment to perform acoustic treatment after oil extraction and one downhole tool of 102 mm diameter and 7000 mm length and comprising three (3) magnetoresistive transducers to target heavy crude oil. Experimental tests on a 500 Bars, temperature-controlled two phase pilot plant ( Figure 10) showed a significant oil recovery. Further tests were conducted in Demkinskoe oil field ( Figure 11), where the initial oil production was around 1.51 tons/day for an initial bottom hole pressure of around 25.93 bars, formation pressure of 49.64 bars a temperature of 23 0 C and water cut of around 10.3 %. The results indicated that following a 24 hours well treatment, an increase of the bottomhole pressure by 2 atm was observed which led to an increase of oil production by around 0.4 tons/day. Further rheological study on a sample taken from the reservoir indicated that the oil viscosity decreased from 183 to 154 mPa*s, which is in good agreement with the theory. shows an interesting result of the vibration amplitude distribution of the downhole tool within a tank (500 mm x 1800 mm area) that mimics the same well condition. Further studies have demonstrated that ultrasonic hydrodynamic treatment leads to higher oil recovery by up to 30% and also helps reducing the water-cut. It is also suggested that sonochemistry treatment can leads to even higher recovery. This led the researchers to design and fabricate an integrated cable that includes power cable, and armored channel to induce chemical agents ( Figure 13). The usage of such cable has the advantage to avoid interrupting the ultrasonic radiation within the well and remove all the associated equipment in order to proceed with the sonochemical treatment. Fig. 12. Distribution of the acoustic field near the downhole tool with a diameter of 102 mm according to the studies performed using a hydrophone at a distance of 500 mm from the lateral radiating surface [17] Fig. 13. Possible design of a cable for sonochemical treatment of wells with highviscosity oil on a permanent basis [17] ...
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... addition, a decrease of 4% of water cut, and an increase of a bottom pressure by up to 30 bars was obtained in both fields. Figure 7 shows the block diagram of the 10 KW ultrasonic generator which was used at the surface. It consists of three main units: the power supply block unit that is fed to a 3 phase 308 V/50Hz power supply, the control block unit that receives borehole data (i.e. ...
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... instrument that consists of a stack of several piezeoelecric sensors (PZT-4) can only operate for relatively short period of time due to the low Currie temperature. More recently, another PZT-5 based ultrasonic sensor that features magnetic orientation was designed and built to deliver a power of up to 100 kW to an array 10-35 kHz ultrasonic probes using a multicore cable that consists of twisted copper wires covered by polythene cover and 30 galvanized steel wire of 1.54 mm diameter (Figure 17). The usage of multicore cable is justified by its high tensile strength as well as its excellent bending resistance, even though its overall length is slightly higher. ...
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... even though its overall length is slightly higher. Figure 18 shows a photograph of the ultrasonic probe that was able to operate at temperatures ranging from -10 to 150 0 C to recover up to 30% of oil. The results have revealed that a long lasting decrease of oil viscosity can be obtained if ultrasonic treatment is combined with chemical agents. Fig. 17:.Power cable used in an ultrasonic-assisted EOR [18] ...
Citations
... Due to the decrease in oil viscosity, interfacial tension, and microstructural changes in the rock, elastic vibrations have a positive enhancing effect on oil recovery during waterflooding [29] samples. Ref. [30] proposes to use nonlinear loading in conjunction with the injection of gas, liquid, or other chemicals. On the large-scale experimental rig [31], it was found that the nonlinear loads increase the fluidity of oil by a factor of 2-3 and increase the oil filtration rate through the porous medium by a factor of 1.2-1.5, arguing that narrow channels in the rocks of the borehole are unblocked (removed) from waxes and asphaltenes, clay particles, and other compounds. ...
This paper presents the results of experimental studies on the filtration of reservoir fluid through the rocks under the influence of nonlinear loads. A laboratory rig is assembled that allows for modeling the flow of fluid from the reservoir into the well during the propagation of elastic waves from the well. It is shown that depending on the permeability of the rock matrix as well as on the concentration of paraffins and asphaltenes in crude oil, the effect of the nonlinear load is different. Three types of sandstone are studied: low, medium, and high permeability. The greatest influence of nonlinear loads is observed in high-permeability sandstone. The effect manifests itself in fully unblocking the pore space from paraffins and asphaltenes accumulated in pore throats and restoring the oil permeability to its original value. In the case of medium-permeability sandstone subjected to nonlinear loads, blocking of the pore space is slow. In the case of low-permeability sandstone, the impact of nonlinear loads does not have a significant effect. When studying water filtration in the presence of residual oil saturation, the effect of nonlinear loads is observed as a mobilization of additional oil not previously involved in the filtration process, which also leads to an increase in the water permeability of the rock.
... Another mathematical model for evaluating the fluid flow in the field of elastic oscillation in a perforated well was developed by Prachkin et al. [20]. In a recent field application review, Meribout [21] suggested that since the application of elastic oscillations is one of the most promising enhanced oil recovery (EOR) methods, combining a vibration treatment with the injection of gas, liquid, and other chemicals into the nearwellbore zone should produce excellent results. According to previous studies [22,23], elastic oscillations have the following effects on rocks: capillary effects, poroelastic motion, thermal effects, increased degassing, and changes in the oil viscosity, mobility ratio, oil displacement by water, and rock permeability. ...
... In most situations, the ultrasonic approach efficiently removes impediments to oil flow, and the benefit of oil recovery can endure for a long period. Amongst other benefits, this approach includes low energy consumption, avoidance of rock-fluid or fluid-fluid interactions, zonal selectivity, real-time monitoring, and its applicability to complex/horizontal and deviated wells [2][3][4][5][6]. ...
The ultrasound method is a low-cost, environmentally safe technology that may be utilized in the petroleum industry to boost oil recovery from the underground reservoir via enhanced oil recovery or well stimulation campaigns. The method uses a downhole instrument to propagate waves into the formation, enhancing oil recovery and/or removing formation damage around the wellbore that has caused oil flow constraints. Ultrasonic technology has piqued the interest of the petroleum industry, and as a result, research efforts are ongoing to fill up the gaps in its application. This paper discusses the most recent research on the investigation of ultrasound’s applicability in underground petroleum reservoirs for improved oil recovery and formation damage remediation.
New study areas and scopes were identified, and future investigations were proposed
... Another mathematical model for evaluating the fluid flow in the field of elastic oscillation to a perforated well is given in [13]. In a recent field application review [14], the authors suggest using elastic oscillations influence on rock as one of the most promising EOR methods, combining vibration treatment with injection of gas, liquid and other chemicals into the near-wellbore zone. According to [15,16], under the action of elastic oscillation on the rock, the effects are observed that are as follows: capillary effects, poroelastic motion, thermal effects, increased degassing, change in oil viscosity, mobility ratio and oil displacement by water as well as rock permeability. ...
The article presents the results of experimental studies of the influence of elastic oscillations on the structure of paraffin oil of a Perm region field. Oil samples are treated by elastic oscillations at a frequency of 22 kHz. As a result of cavitation and an increase in oil temperature, a decrease in the concentration and a decrease in the size of high-molecular paraffin compounds in oil is observed. With an increase in the time of ultrasonic treatment, the intensity of dissolution of paraffins in oil increases. A model of an experimental setup is proposed to study the effect of elastic oscillations on the permeability of a rock during the flow of paraffin oil. The impact of permeability deterioration around the production well on its flow rate is assessed.
... The use of ultrasonic waves to remediate asphaltene deposition is a non-destructive, environmentally friendly, and cost-effective technology that uses a simple ultrasonic downhole tool eliminates the need for specialized chemicals [18]. The method is gaining popularity in the petroleum industry [19], owing to its low energy consumption [18], high adaptability and zonal selectivity during treatment [20,21,22] . ...
... The relatively short range of ultrasonic waves, which normally does not exceed 1 m, is a common drawback in field applications. The depth of penetration is mostly determined by the applied frequency, the nature of the ultrasonic probe, and the density of the rock formation (M. [21]. The lower the frequency, the deeper the penetration of the wave into the formation (M. [21,51] , while increasing the power will improve the cleaning effect. ...
... The depth of penetration is mostly determined by the applied frequency, the nature of the ultrasonic probe, and the density of the rock formation (M. [21]. The lower the frequency, the deeper the penetration of the wave into the formation (M. [21,51] , while increasing the power will improve the cleaning effect. The 20 kHz frequency used in this study has been reported to penetrate up to 10 cm into the formation [22], and was adequate to remediate the near wellbore formation damage induced by paraffin precipitates [41]. ...
Asphaltene deposition around the wellbore is a major cause of formation damage, especially in heavy oil reservoirs Ultrasonic stimulation, rather than chemical injection, is thought to be a more cost-effective and environmentally friendly means of removing asphaltene deposition. However, it seems to be unclear how crucial features like reservoir pore geometries and ultrasonic parameters affect this ultrasound treatment.
In this work, five two-dimensional glass micromodels with different pore geometries were designed to assess the impact of pore geometries on the ultrasonic removal of asphaltene deposition. Experiments were undertaken in an ultrasound bath at a set frequency (20 kHz) and adjustable powers (100 - 1000 W). Direct image analysis before, during and after sonication was used to assess the impact of pore geometry and a change in ultrasonic parameter on the removal of asphaltene deposition. The effectiveness of ultrasound treatment at various sonication periods were found to be reliant on the pore geometries of the individual micromodels. For micromodels with throat sizes 300 µm and pore shapes as circle, square and triangle, an increase in ultrasonic power from 400 to 1000 watt resulted in an increase in the percentage of removed asphaltene deposition after 2 hours from 12.6 to 14.7, 11.5 to 14.63, and 5.8 to 7.1 percent, respectively.
... As a result, they might lead to altering the wettability to water-wet. For surfactant solutions, however, sonication leads to increasing the solubility of the surfactant into the oil, which resulted in drastically diminishing the interfacial tension and the capillary pressure of the trapped oil droplets [71,73]. Figure 8 shows the effect of ultrasonic radiation on the removal of oil from the sample by surfactant solution. ...
The impact of ultrasonic radiation, as an emerging enhanced oil recovery technique, on reservoir fluid properties is of great importance in petroleum engineering. Although the effect of sonication on fluid properties has been widely investigated, the wettability alteration of carbonate rocks via different solutions under ultrasonic radiation has not been considered. In this study, the synergic impact of ultrasonic radiation on the wettability alteration of carbonate rocks was studied by using distilled water, seawater, SDS surfactant, silica nanoparticles, and SDS surfactant–silica nanoparticles solutions. Variance analysis showed that all parameters under ultrasonic radiation, including types of water, surfactant solution, nanoparticles, sonication time, and temperature, were meaningful and had influences on the wettability alteration. The contact angle decreased notably by raising the temperature and sonication time. Ultrasonic waves improved the elimination of chemisorbed fatty acids on the surface, and this could be one of the mechanisms of wettability alteration by the ultrasonic application.
... Both the chemical and physical effects of ultrasound waves have been well exploited in chemistry (sonochemistry) as the chemical effects have the ability to generate free chemical radicals [24], while the physical effects can enhance the reactivity of a catalyst by enlarging its surface area or even by increasing a reaction rate [25]. Meribout (2018) reviewed that enhancing the oil production using ultrasonic treatment (1) was much cheaper than conventional recovery methods, (2) was less-energy demanding, and (3) allows a better control of the ultrasonic wave propagation. As per the same author, the primary challenge is the relatively limited range of ultrasonic radiation (up to 2 m) at the operational resonance frequency, which usually ranges from 20 to 40 kHz [26]. ...
... Meribout (2018) reviewed that enhancing the oil production using ultrasonic treatment (1) was much cheaper than conventional recovery methods, (2) was less-energy demanding, and (3) allows a better control of the ultrasonic wave propagation. As per the same author, the primary challenge is the relatively limited range of ultrasonic radiation (up to 2 m) at the operational resonance frequency, which usually ranges from 20 to 40 kHz [26]. This is to say that this method still suffer from deeper understanding to make meaningful and consistent scientific elaborations despite the wealth of papers covering the topic [27][28][29][30][31][32][33]. ...
The present work investigates the contribution of asphaltene aggregation to bitumen viscosity subject to ultrasound irradiation. A West-African bitumen with a viscosity of 12043 cP at room temperature was sonicated at low (38 kHz) and mild frequency (200 kHz) under controlled gas environment including air, nitrogen (N2) and carbon dioxide (CO2). The rheology of the bitumen, asphaltene content analyses as well as spectral studies were conducted. Herein was found that sonicating the bitumen at 200 kHz under air-environment reduces the initial viscosity up to 2079 cP, which was twice larger than that obtained when a low frequency was used. In respect of the gas environment, it was shown that ultrasound irradiation under N2 environment could lower the bitumen viscosity up to 3274 cP. A positive correlation between the asphaltene content and the viscosity reduction was established. The results from the spectral analyses including Fast Fourier Infrared and the observations from Scanned Electron Microscope were consistent with the rheological studies and led to the argument that the viscosity reduction results from either the scission of long chain molecules attached to the aromatic rings (when the applied frequency was altered under fixed gas environment) or the self-aggregation of asphaltene monomers (when gas environment was changed at fixed frequency).
... Several mechanisms had been identified through the experimental work, such as cavitation, viscosity reduction, heat generation, and emulsification as the driving mechanisms behind ultrasonic oil recovery [1]- [11]. Ultrasonic has several advantages over the conventional EOR techniques, such as zero environmental pollution, lower cost (e.g., up to USD 230,000 for a polymer injection device, while ultrasonic costs USD 90,000), lower energy consumption, better targeting for zones of interest, absence of negative impact on the equipment (i.e., corrosion) and has 4-24 months treatment duration [12], [13]. However, despite these benefits, ultrasonic devices have some limitations, including designing a feasible electronic system that accounts for the well constrains such as size and high downhole pressure and the limited penetration range of the waves (i.e., 1 to 2 m) [13]. ...
... Ultrasonic has several advantages over the conventional EOR techniques, such as zero environmental pollution, lower cost (e.g., up to USD 230,000 for a polymer injection device, while ultrasonic costs USD 90,000), lower energy consumption, better targeting for zones of interest, absence of negative impact on the equipment (i.e., corrosion) and has 4-24 months treatment duration [12], [13]. However, despite these benefits, ultrasonic devices have some limitations, including designing a feasible electronic system that accounts for the well constrains such as size and high downhole pressure and the limited penetration range of the waves (i.e., 1 to 2 m) [13]. VOLUME 5 NUMBER 3 2021 e-ISSN: 26369877 PLATFORM Cavitation creates bubbles in a liquid during the rarefaction cycle of a wave [14]. ...
Ultrasonic waves have a wide variety of applications in a variety of fields. It is used in the oil and gas industry to remove near wellbore damage, and several studies have been conducted to examine its application with waterflooding. Additionally, ultrasonic waves are used in engineering to determine the stability of sediments through dispersion and disaggregation. This study aims to incorporate both the ultrasonic waterflooding aspect with the stability of the sediment by investigating the impact of sonication exposure duration on particle size and oil recovery under waterflooding. Six (6) coarse sand samples were used in the experiment to simulate the porous media found in a sand pack. A sieving test was conducted on each sand sample to obtain its Particle Size Distribution (PSD) curve prior and post sonication. Waterflooding was conducted using 3% NaCl brine as the wetting phase and decane (C10H22) as a non-wetting phase. Ultrasonic waves were applied continuously throughout the waterflooding durations (i.e., 15,30,45 minutes), and both temperature and decane recovery were recorded. The results show that ultrasonic results in minimal additional recovery less than 2%, and an increase in temperature of 2-8°C was observed. However, longer sonication results in higher particle disaggregation, which reduces permeability by15.50%-41.85% and can result in sand production. This study can be continued through investigation on the utilization of cyclic ultrasonic-assisted waterflooding as a technique that may aid in recovery without causing detrital effects to the reservoir sand layer.Keywords: permeability, stability, sonication, dispersion, size distribution
... As oil production abates, the development of technologies for enhanced oil recovery is a worldwide challenge of increasing importance [26]. In chronological order, oil production goes through three stages: primary, secondary and tertiary oil recovery. ...
Power ultrasound, as an emerging green technology has received increasing attention of the petroleum industry. The physical and chemical effects of the periodic oscillation and implosion of acoustic cavitation bubbles can be employed to perform a variety of functions. Herein, the mechanisms and effects of acoustic cavitation are presented. In addition, the applications of power ultrasound in the petroleum industry are discussed in detail, including enhanced oil recovery, oil sand extraction, demulsification, viscosity reduction, oily wastewater treatment and oily sludge treatment. From the perspective of industrial background, key issue and resolution mechanism, current applications and future development of power ultrasound are discussed. In addition, the effects of acoustic parameters on treatment efficiency, such as frequency, acoustic intensity and treatment time are analyzed. Finally, the challenges and outlook for industrial application of power ultrasound are discussed.
... For heavy oil production, ultrasonic wave can induce the aquathermolysis reaction to reduce the viscosity of heavy oil and eventually lead to the improvement of oil flow ability and recovery [13]. Some researchers indicated that ultrasonic waves are suitable for removing plugging materials caused by drilling mud or paraffin near the wellbore regions and exhibit a cost-advantage compared with the traditional methods including hydraulic fracturing and acidizing [14,15]. Recent field applications have coupled ultrasonic waves with traditional EOR methods to further improve oil recovery. ...
... Firstly, we needed to treat the crude oil samples and core slices by ultrasonic waves with different frequencies (15,18,20,25,28 kHz). We put 200 g crude oil or a core slice into a self-made high-temperature and high-pressure reaction tank equipped with the ultrasonic generator. ...
... In order to verify the effects of ultrasonic waves on the compounds of light crude oil, we adopted FT-IR to determine the chemical bond changes of oil sample treated by ultrasonic waves with different frequencies (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). Fig. 7 shows the infrared spectra of crude oil before and after ultrasonic treatments and some typical characteristic wave numbers have been marked. ...
Water flooding is one of widely used technique to improve oil recovery from conventional reservoirs, but its performance in low-permeability reservoirs is barely satisfactory. Besides adding chemical agents, ultrasonic wave is an effective and environmental-friendly strategy to assist in water flooding for enhanced oil recovery (EOR) in unconventional reservoirs. The acoustic frequency plays a dominating role in the EOR performance of ultrasonic wave and is usually optimized through a series of time-consuming laboratory experiments. Hence, this study proposes an unsupervised learning method to group low-permeability cores in terms of permeability, porosity and wettability. This grouping algorithm succeeds to classify the 100 natural cores adopted in this study into five categories and the water flooding experiment certificates the accuracy and reliability of the clustering results. It is proved that ultrasonic waves can further improve the oil recovery yielded by water-flooding, especially in the oil-wet and weakly water-wet low-permeability cores. Furthermore, we investigated the EOR mechanism of ultrasonic waves in the low-permeability reservoir via scanning electron microscope observation, infrared characterization, interfacial tension and oil viscosity measurement. Although ultrasonic waves cannot ameliorate the components of light oil as dramatically as those of heavy oil, such compound changes still contribute to the oil viscosity and oil-water interfacial tension reductions. More importantly, ultrasonic waves may modify the micromorphology of low-permeability cores and improve the pore connectivity.
