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Experimental study of ultrasonic radiation on growth kinetic of asphaltene aggregation and deposition

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Ultrasonic treatment as an economical and green technology has been much attended in petroleum industry, especially for inhibition and removal of asphaltene deposition in the near wellbore region. The performance of ultrasonic waves is affected by different parameters such as time, power, frequency, type of radiation, etc. In this communication, the effects of duration of ultrasonic radiation, power and stability on asphaltene aggregation were evaluated from kinetic point of view. In fact, the optimal radiation conditions were determined by comparing the growth kinetics and size distribution of asphaltene particles. The optimal exposure time and power of ultrasonic radiation for the oil sample were obtained 150 sec and 40 W, respectively. In addition, the negative effect of time duration on the aggregated asphaltene particles diameter was observed. The effect of ultrasonic on prevention and removal of asphaltene deposits was examined by observation of changes in asphaltene particles diameter. The results demonstrated the beneficial effect of ultrasonic waves on inhibition of asphaltene deposition. In order to investigate the effect of ultrasound on asphaltene deposition in porous media, the oil sample was radiated with ultrasound at the most optimal conditions, which were obtained in the previous experiments. Moreover, the trend of asphaltene particles deposition in porous media (micro model) at optimal conditions was compared to the same oil sample without ultrasonic radiation. Comparison of pressure drop curves showed that the use of ultrasound in determined optimum conditions reduces the amount of asphaltene deposition. This article is protected by copyright. All rights reserved
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Article
Experimental Study of Ultrasonic Radiation on Growth Kinetic of Asphaltene
Aggregation and Deposition
Marziyeh Salehzadeh 1, Ali Akherati2, Forough Ameli3, Bahram Dabir*, 1, 2
1Department of Petroleum Engineering, Amirkabir University of Technology, Tehran, Iran
2Department of Chemical Engineering, Amirkabir University of Technology
3Islamic Azad University of Technology, North Tehran Branch
*Corresponding author: Bahram Dabir (email address: drbdabir@aut.ac.ir)
This article has been accepted for publication and undergone full peer review but has not
been through the copyediting, typesetting, pagination and proofreading process, which may
lead to differences between this version and the Version of Record. Please cite this article as
doi: [10.1002/cjce.22593]
Received 17 August 2015; Revised 29 September 2015; Accepted 16 November 2015
The Canadian Journal of Chemical Engineering
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DOI 10.1002/cjce.22593
This article is protected by copyright. All rights reserved
Abstract: Ultrasonic treatment as an economical and green technology has been
much attended in petroleum industry, especially for inhibition and removal of asphaltene
deposition in the near wellbore region. The performance of ultrasonic waves is affected by
different parameters such as time, power, frequency, type of radiation, etc. In this
communication, the effects of duration of ultrasonic radiation, power and stability on
asphaltene aggregation were evaluated from kinetic point of view. In fact, the optimal
radiation conditions were determined by comparing the growth kinetics and size distribution
of asphaltene particles. The optimal exposure time and power of ultrasonic radiation for the
oil sample were obtained 150 sec and 40 W, respectively. In addition, the negative effect of
time duration on the aggregated asphaltene particles diameter was observed. The effect of
ultrasonic on prevention and removal of asphaltene deposits was examined by observation of
changes in asphaltene particles diameter. The results demonstrated the beneficial effect of
ultrasonic waves on inhibition of asphaltene deposition. In order to investigate the effect of
ultrasound on asphaltene deposition in porous media, the oil sample was radiated with
ultrasound at the most optimal conditions, which were obtained in the previous experiments.
Moreover, the trend of asphaltene particles deposition in porous media (micro model) at
optimal conditions was compared to the same oil sample without ultrasonic radiation.
Comparison of pressure drop curves showed that the use of ultrasound in determined
optimum conditions reduces the amount of asphaltene deposition. This article is protected by
copyright. All rights reserved
Keywords: asphaltene aggregation, asphaltene deposition, ultrasonic wave, Asphaltene
particles diameter, Micromodel study
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INTRODUCTION
Crude oil is a mixture of different compounds including saturated hydrocarbons,
aromatics, resins and asphaltenes. Among these compounds, asphaltene is the most
problematic one due to its deposition on the reservoir rock or production facilities.[15] As
Zendehboudi et al.[6] stated, asphaltene deposition in reservoir rock, especially in the near
wellbore region, causes serious problems such as formation damage and permeability
reduction. These lead to production rate reduction as well as increase in production costs. It
should be stated that only suspended asphaltene might deposit and block the formations.
Moreover, various techniques have been developed for flow analysis in porous media and
different methods have been used to remove and prevent asphaltene deposition in the tubing,
flow lines, surface facilities, and near wellbore region. These methods can be classified as: 1)
mechanical methods, 2) chemical methods, 3) thermal methods, and 4) Other methods
including bacterial treatment, production techniques and facilities modifications, applying
ultrasonic and combination of two or more methods. Disadvantages of some of the above
mentioned techniques include, expensive application, limitation of the equipment involved
and time, plugging the perforations, increasing the stability of oil-in-water emulsions,
environmental safety and personal hazard concern and harm to the formation.[79]
Over the last decades, ultrasound method as an economical and environmentally
friendly technology has been much attended for prevention and treatment of small deposits in
the wellbore, production facilities and near wellbore region.[10-14] Recently, ultrasonic waves
have been introduced as a useful method for enhancing oil/heavy-oil production, crude oil
upgrading and prevention or removal of asphaltene deposits from the wellbore and near
wellbore region.[13,1521] In the following part, the most relevant studies on application of
ultrasonic waves in oil industry are presented.
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In 1994, Gollapudi et al.[22] evaluated the effect of ultrasonic on removing asphaltene
from sand-asphaltene column. In this study, they observed a considerable improvement in
flow rate to over 500 % at the output control setting after two minutes ultrasonic treatment.
Later, Aarts et al. investigated the effect of ultrasonic radiation on the enhancement of liquid
flow in the porous medium.[10] In 2000, Roberts et al.[8] carried out a study to determine the
role of using ultrasonic energy in formation damage reduction. Their results demonstrated
that ultrasonic cleaning may be a viable method for treating paraffin problems in the near-
wellbore region. Afterward, Gunal and Islam[23] conducted a study to compare the ultrasonic
and electromagnetic waves' effects on the rheological behaviour of the crude oil. In 2004,
Shedid and Attallah[7] studied the asphaltene behaviour of oil to investigate the effect of
temperature and solvent concentration on the series of experiments. Microscopic studies and
differential thermal analyses (DTA) were carried out to analyze the results. They concluded
that ultrasonic radiation reduces the size of asphaltene flocks and the oil viscosity. Then,
Shedid et al.[24] discussed the effects of ultrasonic radiation on the asphaltene clusters
alterations and permeability damage due to asphaltene deposition. According to the results,
the ultrasonic radiation decomposes the clusters of asphaltene into finer sizes in that crude oil
and improves permeability damage. Comparison of scanning electron microscope (SEM)
images revealed that increase in frequency leads to three important changes in the rock
surfaces including the more intensity of the surface roughness, increase in depth of created
micro-cavities, and creating micro-fractures to connect these cavities.
In 2011, Amani and Najafi[13] applied viscometery tests and confocal microscopy to
investigate the flocculation of oil exposed to ultrasonic waves. They observed a specific
radiation time, which has the lowest potential for generating macro-structure flocks. On the
other hand, in this radiation time, the value of viscosity is locally minimum. They claimed
that the heavy oil samples have greater optimum radiation time in comparison to the lighter
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crude oils. Najafi et al.[25] studied the asphaltene flocculation kinetics of the sonicated oils.
Their results indicated that radiation of ultrasonic waves would change the asphaltene
flocculation kinetics in crude oils and reduce the possibility of formation of macrostructure
aggregates. In addition, the existence of an optimum value for radiation time was noted in
which the viscosity and the flocculation rate of asphaltenic crude oils reduce to their
minimum values. Recently, Mousavi et al.[26] studied the effects of ultrasonic waves on
rheological properties of the oil as well as the effect of temperature on viscosity behaviour of
heavy crude oils. They concluded that the ultrasonic radiation could increase the stress value
required for flow of the crude oil samples (yield stress). However, a radiation time was found
in which the yield stress was the minimum and ease of flow was the highest value.
Temperature sweep tests indicated that the temperature increase due to ultrasonic radiation
did not lead to any physical and chemical changes.
Most of the previous studies investigated the effect of ultrasonic waves on the
removal of the asphaltene deposits in the near wellbore region. Other parameters of ultrasonic
radiation, such as particle growth and its effect on the reduction of asphaltene deposition
were not included in previous models. In this paper, other parameters including, the time and
radiation power which are effective on ultrasonic efficiency, have been studied. To this end,
the growth kinetics and particles average size distribution analysis have been investigated.
Besides, the effects of ultrasonic waves on the inhibition and removal of asphaltene
deposition have been studied in details. One of the main issues of this research was studying
the stability of ultrasonic radiation; as a result, optimum values of the parameters should be
determined to test the stability of ultrasound effect. Moreover, in this study the ultrasonic
effect was studied on prevention or removing the asphaltene flocculation. Finally, asphaltene
deposition trend was studied for an oil sample exposed to the optimum conditions of radiation
and the result was compared to a non-sonicated one.
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EXPERIMENTAL
Test Fluids
The representative single-phase sample of this work was obtained from a light crude
oil reservoir in the Southwest of Iran. The crude oil properties are represented in Table 1. As
it is clear, the asphaltene content of the crude oil was 5.3 % (gAsph/goil). Decane was used as a
precipitant in all experiments owing to its more stability at higher temperatures.
Methodology of Kinetic Experiments
The ultrasonic radiation was applied using a wave generator with the frequency of
20 kHz. All crude oil samples were subjected to a constant ultrasonic frequency, with
different radiation powers and exposure times. To analyze the distribution size of asphaltene
particles, a STERIO microscope with magnification of 400X was used. The microscope was
connected to a PC and a CCD camera. The images of the flocculated asphaltenes were stored
in raw format of 4000*3000 pixels and then analyzed using ANALYSIS software which
delineates different characteristics of particles such as mean diameter of each particle, fractal
dimension of particles, mean area, etc. in the samples. In the experimental procedure, crude
oil samples (each sample is 0.02 L) were placed in a 0.05 L beaker and exposed to ultrasonic
waves at different exposure times and powers. After ultrasonic radiation, the oil samples were
cooled to the ambient temperature of 299.5 K and prepared for the next step of experimental
studies. To analyze the distribution size of asphaltene particles, n-decane was added to
samples, and at pre-specified times of flocculation, the samples were evaluated using the
microscope. In kinetic section, the presented numbers are based on particle size analysis of
pictures which were taken at specified times. We selected some regions of the picture, for
analyzing the mean diameter of particles, which may create a small error. Pictures analysis
for calculating the mean diameters is based on particles area and then representing an equal
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diameter to that area. It is possible that there exists a little error for detection of particle
diameter edges, which is unavoidable. In addition, crude oil is a heterogeneous liquid which
may cause some errors in results.
Experiment Procedure
In order to find the optimum values of parameters which influence the ultrasonic
efficiency, ten experiments were conducted. The flocculation kinetic of asphaltene particles
was monitored in all of the tests. First, it was necessary to determine the asphaltene
flocculation onset (AFO) in the presence of decane. The precipitant to oil ratio should be
constant during the tests. Radiation of the ultrasonic waves increases the temperature of the
fluid; in high temperature conditions, most of the precipitants partially evaporate. Therefore,
decane, which is more stable at high temperatures, was used as a precipitant in experiments.
All the experiments were performed in AFO, the ratio of adding precipitant (decane) to oil
was about 1.53, which ensures the flock’s formation.
In these sets of experiments, the effects of time and power of ultrasonic radiation, the
stability of its effect and also the influence of ultrasonic waves on both prevention and
removal of asphaltene deposits were investigated using particle size distribution analysis. All
of the experiments were repeated three times to ensure the repeatability of the results.
However, only the average value of results have been are reported. Also, error bars of the
results have been illustrated in the figures.
Methodology of Micromodel Experiments
A schematic diagram of the asphaltene deposition experiment is illustrated in Figure 1. The
synthetic porous media of this research was a glass micro model consisting of glass beads in
the range of 0.0003 to 0.0006 m, and input and output flows which were embedded on both
sides. Injection lines (0.0025 m ID transparent plastic tubing) were connected via an
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angiocath connector to the micro model for installation of the valves and adjustment of the
input flows of the sonicated oil and precipitants. Two constant-rate programmable syringe
pumps (BS-8000/9000 from Braintree Scientific, U.S.A.), with designed throughput of 2.8e-8
L/s to 8.3e-5 L/s, were used in the crude oil and the precipitant streams. A well-calibrated
(1.5e+5 Pa range) pressure transducer, was used to measure the pressure difference at micro
model. As the micro model was discharged to the atmosphere, the recorded gauge pressure
was the pressure drop across the micro model. Before starting a new run, the micro model
and the injection lines were adequately cleaned to remove the precipitated asphaltene from
the previous runs.
Procedure
In the second series of experiments, the oil sample was exposed to the pre-determined
optimum conditions of ultrasonic radiation, and then the deposition of asphaltene was
monitored by adding the precipitant and measuring the pressure drop across a synthetic
porous media. As we know, some asphaltene particles normally deposit on the porous
medium. Therefore, it seems essential to investigate the mechanism of asphaltene deposition
after ultrasonic treatment.
The precipitant to oil ratio of the samples was set more than AFO value in these tests.
The values of oil and precipitant flow rates were 1.38e-7 L.s-1 and 5.5e-7 L.s-1, respectively.
The injection flow rates of oil and the precipitant were adjusted to achieve the steady state
conditions and laminar regime in micro model. Two experiments were performed to observe
the effect of ultrasound on asphaltene deposition formation. For the first experiment, the oil
sample without ultrasound radiation was precipitated by decane. In the second experiment, oil
was radiated by ultrasonic waves at predetermined optimal conditions. In both of the
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experiments, the pressure drop trends in the synthetic porous media were recorded. The
pressure drop of the system was due to addition of the precipitant into the micromodel.
The pressure drop was recorded while the system reaching to steady state conditions.
Then, the oil and precipitant rates were adjusted for observation of asphaltene deposition
change in the micro model. It should be noted that changing in thermodynamic conditions
such as pressure, temperature and composition leads to instability of asphaltene. Certainly,
performing experiments in real conditions will illustrate more valuable results, but due to
limitations in laboratories' facilities, most of the studies in this field follow the same
approach; for instance, researchers use a normal alkane for precipitating asphaltene instead of
changing the pressure or temperature conditions that are more similar to real conditions.
RESULTS AND DISCUSSION
Kinetic of Asphaltene Agglomeration
Ultrasonic radiation time
In the first part of kinetic tests, identical samples of the crude oil were radiated with
ultrasonic waves. Different exposure times, including 0, 150, 300, 450 and 600 seconds were
considered in investigating the existence of an optimum ultrasonic radiation time. It has been
proved that oil samples have an optimum time for ultrasonic radiation, and it has been
observed that heavier crude oil samples have greater optimum radiation time.[26] Figure 2
represents the images of asphaltene clusters for non-radiated and radiated oil samples after 9
mins of flocculation. The termination time was evaluated when the particle sizes remained fix
and there were not any changes in asphaltene particle sizes. Therefore, we did not continue
the experiments for longer time in such conditions. Figure 3 demonstrates the average
diameter of asphaltene particles at different exposure times as a function of time. As can be
seen from this figure, the optimum exposure time is 150 seconds. The diameters of the
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asphaltene particles are minimum at this time, and the decrease in asphaltene particles
growth rate is obvious as well. The main reason for reduction of diameter size is
disintegration of asphaltene molecules. Ultrasonic wave breaks the heavy molecules and long
chain structures and forms free radicals which lead to decrease in the diameter of asphaltene
flocks. Increase in exposure time from 0 to 150 seconds leads to decrease in particles
diameter; however, after this optimum time, flocks with larger size will be formed. Due to
polymer-like behaviour of asphaltene molecules, the effects of ultrasonic radiation on
chemical bonds of molecules varies with change in radiation frequency, power, and duration.
At optimum radiation time, the asphaltene particle size is minimum. Smaller molecules in
diameter, lead to reduction of fluid viscosity. After the optimum radiation time, broken
structures and free radicals integrate and form heavier and more complex compounds. This
phenomenon increases the fluid viscosity. In most of the previous studies, the optimum
radiation time was determined by measuring the viscosity at different radiation times [27-31].
According to the results of this study, ultrasonic radiation has prominent effects on particle
size distribution and aggregation process.
Power of ultrasonic radiation
To study the effect of radiation power, oil samples were exposed to ultrasonic waves
at different radiation powers, including 30, 40, and 50 W for 150 seconds (the optimum time
for this oil sample was obtained in the first part of the experiments). An increase in the
radiation power, leads to increase in sample temperature. Previously published studies proved
that temperature increase due to ultrasonic radiation is not the reason for the breakdown of
the asphaltene molecules and other physical and chemical changes.[27] In this study, the
temperature was constant during all the experiments. Figure 4 presents the asphaltene
particles in different conditions of ultrasonic radiation power after 9 minutes of flocculation,
and indicates that this power has an optimum value in which the size of flocks is minimum.
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Besides, Figure 5 shows the average diameter of particles versus time for different radiation
powers, which confirms the previous results as well. The existence of optimum radiation
power in the mentioned range is explained identical to the existence of optimum exposure
time. Nonetheless, observation of diverse results in the higher powers of ultrasonic radiation
is a feasible treatment.
Permanency of ultrasonic effect
To investigate the stability of ultrasonic effect, an oil sample was exposed to
ultrasound radiation for 150 seconds with the power of 40 W. Aggregation kinetics of
particles was studied by adding the precipitant to the same portions of the oil sample. The
experiments were conducted in three different steps for measuring the aggregates size,
including immediately after reaching the sample to the ambient temperature, one day and four
days after using ultrasonic radiation, respectively. Figure 6 depicts the asphaltene particles
size distribution versus time after adding the precipitant to three oil samples in comparison to
an oil sample without exposing to ultrasonic radiation. Diameters of asphaltene particles
which were maintained one day or a few days after radiation, increased even more than those
of the non-sonicated sample. Figure 7 illustrates this phenomenon. This is not a challenging
issue, since ultrasonic radiation is normally used to remove or prevent the formation damage.
Effect of ultrasonic on either prevention or removing of asphaltene deposits
Finally, to observe the effect of ultrasound on prevention and removal of the
asphaltene flocculation in a defined exposure time (here it is the optimal conditions), three
experiments were performed based on comparing the size and growth kinetics of asphaltene
particles: In the first experiment, oil sample was analyzed without ultrasonic radiation. In the
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second test, oil sample was exposed to ultrasonic waves and the precipitant was added
instantly to illustrate the prevention effects. Radiation time and power were considered at
their optimum values. In the third experiment, the precipitant was added to the oil sample
before exposure to the ultrasonic radiation to observe its effect on removing asphaltene
flocculates. The recorded time is the time after exposure to ultrasound radiation. To evaluate
the effect of ultrasound on removing asphaltene deposits, a mixture of oil and precipitant was
timed to form some precipitates. After the formation of precipitates while their growth
continued, the mixture was exposed to ultrasonic waves. The size of precipitated particles
depends on the time passing after the ultrasonic exposure. Hence, to evaluate the waves'
effects, the final diameter of the particles was compared. The images of asphaltene particles
at the end of these tests are presented in Figure 8. As it is shown in Figure 9, the use of
ultrasound waves leads to a reduction in diameter of the asphaltene particles and their growth
kinetics. On the contrary, applying the ultrasonic radiation after particle formation results in
formation of larger particles in size and diameter, even larger than particles which were
formed in experiments without ultrasonic radiation. The effects of ultrasound on removing
asphaltene precipitation have been widely discussed in many articles. As already mentioned,
Shedid[24] observed that the use of ultrasonic waves causes changes such as creating micro
fractures or micro-cavities in rocks. Almost in all of the previous studies that evaluated the
ultrasound effect on removing asphaltene deposition, the sediment formation environment
such as cores was influenced by these waves as well. Hence, investigation of ultrasonic
effects on the fluid without considering its media seems essential. Improvement in their
results may be due to changes made in the environment and turbulences caused by
application of these waves. Depending on the oil types or applied conditions (parameters that
influence the effectiveness of ultrasound or types of used precipitant and formed deposits), it
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is possible for these waves to have positive effects on the fluid and asphaltene formation and
also to reduce the size of asphaltene particles.
Hydrodynamics of Asphaltene Deposition in Synthetic Porous Media
It has been clarified that distribution of asphaltene particle size plays an important
role in permeability impairment.[25,26,32] Relatively large particles have a noticeable chance to
plug the pore throats of the rock. Plugging the throats will decrease the permeability;
therefore, investigating the particle size distribution seems indispensable. Ultrasound could
reduce the generation of macrostructure flocs, which noticeably reduces the negative impacts
of asphaltene deposition on absolute and relative permeability of reservoir rocks.[17] In order
to analyze the particle size, which is one of the most effective parameters for asphaltene
deposition in porous media, the effect of ultrasonic radiation on the asphaltene deposition
changes was monitored. In the majority of the previous studies, the effects of ultrasound on
improving the permeability in the asphaltene-induced damaged samples have been
investigated, while very few studies delved into the effects of this phenomenon on asphaltene
deposition changes in porous media when fluid is exposed to ultrasound radiation. These
experiments were conducted for comparison of the pressure drop variations through a
synthetic porous medium (micro model) for an oil sample without sonication and an oil
sample which was exposed to ultrasonic waves at optimum conditions. Figure 10 represents
the pressure change versus time. The decreasing trend at the beginning of the graph is
attributed to the lower viscosity of the oil + decane mixture than the oil viscosity. As
explained above, at the beginning of each test, micro model was saturated with specific oil
sample at the determined rate and after reaching to steady state conditions, the oil and
precipitant rates were adjusted to achieve the rate of oil in steady state conditions. In this
condition, the only reason for decreasing the pressure is variation of the fluid viscosity.
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Afterward, the pressure drop between two sides of the micro model increases. As known, the
mixture viscosity is constant during the experiments, hence, increase in pressure drop is
attributed to the simultaneous effect of surface deposition and pore-throat plugging of
precipitated asphaltene particles. This growth is followed by a sharp pressure drop which
indicates the entrainment of asphaltene deposits. Then, increase in asphaltene deposits results
in reduction of hydraulic radius of porous media. This reduction is an outcome of void
volume reduction. As asphaltene particles are deposited inside the pore channels, void
volume of the channel is reduced and the pore surface area is increased. Both of these events
may decrease the value of the hydraulic radius and consequently affect the fluid flow through
the porous media. This leads to pressure drop increases in this stage. Due to the increase in
fluid velocity and stress on sediments, a portion of the sediments is detached and improves
the fluid path; therefore, the reduction of pressure drop is observed in the system. Then, the
amount of asphaltene deposition increases again and this phenomenon occurs periodically.
Comparing the pressure drop curve of the two cases indicates that pressure drop of the oil
under ultrasonic radiation is less than that without ultrasound radiation. The difference
between these two cases can be attributed to oil viscosity, amount of precipitated asphaltene
and entrainment of asphaltene particles. Application of ultrasound waves (at optimum
conditions) reduces the oil viscosity, and this results in less pressure drop. Moreover, the
amount of precipitated asphaltene in the sample under radiation is less than the other case.
Besides, the radiated oil sample shows a more and earlier time of entrainment of asphaltene
deposits. Increase of fragmentation rate in the radiated sample is due to loosening of the
formed asphaltene deposits compared to those in the sample without ultrasound radiation.
Decrease of the pressure drop and lower values of critical velocity for entrainment in the
sonicated oil sample are related to the lower thickness of the deposited layer and
subsequently to the improvement of permeability. As a result, the ultrasonic waves postponed
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the pores blockage and reduced the negative effects of asphaltene deposition. The reported
trend can be extended to the high pressure experimental conditions with different values of
pressure drop. However, if there are no limitations in pressure transducer and pumps, following
up the trend of pressure drop, leads to the following treatments. First, the periodic trend of
pressure drop will continue in higher pressure values. Second, the complete blockage of pores
leads to a severe increase in pressure drop. Moreover, the nature of the deposited asphaltene,
which stems from adding the precipitant is inherently different from that, is formed by pressure
drop. Therefore, investigation of this phenomenon for asphaltene deposition due to pressure drop
will reveal useful information.
Application of ultrasonic wave technology can affect the particle size distribution of
asphaltene particles in a way which leads to reduce possibility of formation of macrostructure
aggregates and asphaltene deposition problems. Therefore, ultrasonic stimulation can be
applicable to inhibit the asphaltene-induced damage in the vital zones such as the near well
bore region. Moreover, cavitation, heat generation, and viscosity reduction are three of the
mechanisms leading to increase in oil recovery under ultrasound. Hence, using ultrasonic
technology has a prominent effect on reduction of problems especially in the production part.
The results of this study can be applied in the near wellbore region, wellbore and pipelines.
The present study was treated as a primary step for application of ultrasonic technique in real
conditions and dimensions. This study should be developed to be applied in real conditions.
The first part of our study can be generalized in the three stated regions. However, in the
second part of the experiments which was studying the mechanism of asphaltene deposition
in synthetic porous media, the main effort was focused on the near well bore region.
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CONCLUSIONS
In this study, the effects of ultrasound waves on an oil sample from one of southern
Iranian oil fields were investigated. To this end, kinetics and the distribution diameters of the
asphaltene particles were thoroughly analyzed. The main findings of this study are as follows:
1. There are optimum values for the time and power for ultrasonic radiation in which
the particles’ diameters and their growth rates are minimum.
2. For the current oil sample, the optimum values of the time and radiation power were
obtained 150 seconds and 40 W, respectively.
3. Above these optimum values, ultrasonic radiation has negative effects on particles
size distribution, growth kinetic and oil viscosity.
4. For the present oil sample, ultrasound radiation is introduced as a preventive
technique to inhibit the formation of asphaltene deposits, because ultrasonic radiation
did not lead to the removal of the deposits.
5. Investigation of the ultrasound effects on asphaltene deposition in a synthetic porous
medium (micro model) demonstrated that using the ultrasound waves in optimal
conditions reduces the amount of sediments. In addition, entrainment of asphaltene
deposits was occurred at an earlier time, which can be attributed to loosening of
precipitated asphaltene due to ultrasound radiation.
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Figure Caption:
Figure 1. Set-up for the asphaltene deposition experiment in the micro model.
Figure 2. After 9 min of flocculation with n-decane for nonsonicated samples and different
exposure times of ultrasonic radiation under power of 40W and frequency of 20kHz : (a)
nonsonicated; (b) sonicated for 150 sec; (c) sonicated for 300 sec; (d) sonicated for 450 sec;
(e) sonicated for 600 sec.
Figure 3. The effect of ultrasonic radiation time on particles diameter.
Figure 4. Asphaltene particles after 9 min of flocculation with n-decane, 150 sec and 20 kHz
of ultrasonic radiation, for different ultrasonic radiation powers: (a) 30 W; (b) 40 W; (c) 50
W.
Figure 5. The effect of ultrasonic radiation power on particles diameter.
Figure 6. Stability of ultrasonic effect with elapsed time.
Figure 7. Flocculated asphaltene particles of oil exposed to 150 sec, 40W and 20 kHz of
ultrasonic radiation, 9 min after adding n-decane for different times after radiation in the
same sample: (a) immediately; (b) one day; (c) 4 days
Figure 8. Asphaltene particles at the end of test performed to investigate the ultrasonic effect
on prevention or removing of asphaltene, oil samples exposed to 150 sec, 40W and 20 kHz of
ultrasonic radiation: (a) nonsonicated; (b) prevention; (c) removing.
Figure 9. Effect of ultrasonic radiation on asphaltene deposits prevention: oil 150 s (oil
sample exposed to ultrasonic before adding the precipitant); oil+ decane 150 s (oil+ decane
mixture exposed to ultrasonic); oil (nonsonicate oil).
Figure 10. Comparison of pressure drop in micro model for oil without ultrasonic radiation
and oil with
radiation at optimum conditions.
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Table 1: General specifications of the crude oil
Specification
Unit
Value
Gravity of dead Oil
ͦ API
27.9
Viscosity of oil at room temperature
cP
3.34
Saturates
(mass fraction)
0.5960
Aromatics
(mass fraction)
0.2630
Resins
(mass fraction)
0.0880
Asphaltenes
(mass fraction)
0.0530
H2S
(mole fraction)
0
CO2
(mole fraction)
0
C1
(mole fraction)
0
C2
(mole fraction)
0.0008
C3
(mole fraction)
0.0172
iC4
(mole fraction)
0.0070
nC4
(mole fraction)
0.0265
iC5
(mole fraction)
0.0179
nC5
(mole fraction)
0.0179
C6
(mole fraction)
0.0927
C7
(mole fraction)
0.0752
C8
(mole fraction)
0.0919
C9
(mole fraction)
0.0740
C10
(mole fraction)
0.0557
C11
(mole fraction)
0.0466
C12+
(mole fraction)
0.4766
C12+ molecular weight
-
418
Sp.Gr. of C12+ Fraction @ 60/60 oF
-
0.9459
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
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Figure 6
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Figure 7
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Figure 8
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Figure 9
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Figure 10
... 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] . ...
... Laboratory studies of ultrasonic treatment of formation damage are mainly conducted in one of two ways: in microfluidics/micromodels (capillary dominated flow) [23,19] or in a coreflooding experiment [24,25,20,26,27,28,29] . Glass micromodels have characteristics that are comparable to those of sandstone reservoir rock [6] and may be utilized to observe processes at the pore level under dynamic settings. ...
... Salehzadeh et al. [19] investigated the effects of ultrasonic waves (frequency 20 kHz, power 40 W) on asphaltene flocculation and deposition using micromodels. In their experiment, they used a preventative strategy and observed that ultrasound inhibited asphaltene deposition. ...
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