Subscriber access provided by BOSTON UNIV

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth StreetN.W., Washington, DC 20036Published by American Chemical Society. Copyright © American Chemical Society.However, no copyright claim is made to original U.S. Government works, or worksproduced by employees of any Commonwealth realm Crown government in the courseof their duties.

Article

The Effect of Resins on Asphaltene Deposition and the Changes ofSurface Properties at Different Pressures, a Microstructure Study

Farhad Soorghali, Ali Zolghadr, and Shahab AyatollahiEnergy Fuels, Just Accepted Manuscript • DOI: 10.1021/ef500020n • Publication Date (Web): 10 Mar 2014

Downloaded from http://pubs.acs.org on March 12, 2014

Just Accepted

“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are postedonline prior to technical editing, formatting for publication and author proofing. The American ChemicalSociety provides “Just Accepted” as a free service to the research community to expedite thedissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscriptsappear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have beenfully peer reviewed, but should not be considered the official version of record. They are accessible to allreaders and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offeredto authors. Therefore, the “Just Accepted” Web site may not include all articles that will be publishedin the journal. After a manuscript is technically edited and formatted, it will be removed from the “JustAccepted” Web site and published as an ASAP article. Note that technical editing may introduce minorchanges to the manuscript text and/or graphics which could affect content, and all legal disclaimersand ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errorsor consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Page 1 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

1

The Effect of Resins on Asphaltene Deposition and

the Changes of Surface Properties at Different

Pressures, a Microstructure Study

Farhad Soorghali, Ali Zolghadr, Shahab Ayatollahi*†

(Enhanced Oil Recovery (EOR) Research Centre, School of Chemical and Petroleum

Engineering, Shiraz University, P.O. Box 7134851154, Shiraz, Iran)

*S Supporting Information

ABSTRACT: Asphaltene deposition has hindered oil production from asphaltenic oil reservoirs

through deposition in reservoir rock and surface facilities. This paper investigates the effect of

resin on asphaltene deposition at different pressures. To investigate the asphaltene deposition in

the presence of resins at reservoir temperature and different pressures, a PVT (Pressure, Volume,

Temperature) visual cell was designed. A high resolution microscope and image processing

software were used to detect and determine the amount of deposited asphaltene as well as its size

distribution at different conditions. Two types of Iranian crude oil with different potential of

deposition (low and high) were used in this work. In the first stage, the amount of asphaltene

deposition and the changes of surface properties were recognized through depressurizing process

with and without the presence of resins in the fluid. The wettability changes as the sign of

surface properties was studied by contact angle measurement and also for further investigation,

the AFM technique was used. The results verify that the amount of asphaltene deposition

increases when the pressure increases, and the quantity of asphaltene deposition decreases as

resin to asphaltene ratio in these samples increases. At high ratios of resin to asphaltene, the

Page 2 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

2

asphaltene was found to be more stable. However, the results showed that as the pressure

increases the stability of asphaltene decreases more than that it was expected. The surface

property changes indicate that in the presence of resins, the surfaces become more water wet and

their roughness decreases.

INTRODUCTION

A petroleum fluid is generally divided into three parts: (1) oils (that is, saturates and

aromatics), (2) resins and (3) asphaltenes.1-3 This partitioning is very broad; each part of the

petroleum fluid also consists a wide range of molecules with varying structures and properties.4

If the components of crude oil are investigated in terms of polarities, asphaltene and resins are

polar molecules, while the oils are either non-or mildly polar.5, 6 For most of the crudes, they

contain more saturates and aromatics , however, even small concentrations of asphaltenes would

affect the quality of the crude oil because they can easily aggregate and deposits on the surfaces

as well affecting their rheological properties.7-9 Asphaltene is defined as part of crude oil, which

is insoluble in normal alkanes such as n-heptane but soluble in aromatic solvents.8-10 Also,

asphaltenes are formed from poly aromatic nuclei with aliphatic side chains and rings. These

compounds in the presence of aromatic hydrocarbons (or other polar solvents) associate and

form micellar aggregates (Nano scale).11-14 It is realized that asphaltenes contain aromatic

compounds also different acidic and basic functional groups.15 Asphaltene problems

considerably affect the economics and technical feasibility of petroleum production either

through situ deposition in the reservoir, in the wellbore and at the surface production facilities

including the transportation systems.16-18 Asphaltene deposition has also been reported in deep

water offshore production facilities.19-21 Asphaltene aggregates (Macro scale) when some of the

Page 3 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

3

fluid properties such as composition, temperature, and pressure are changed during the

production and transportation.22, 23 The most important parameters that promote asphaltene

aggregation are the amount of paraffin, temperature , and pressure changes.24, 25 Resin is another

parameter that could affect asphaltene aggregation. Resins, is known as a fraction of the

deasphalted crude oils that is adsorbed in silica gel and is extracted with polar solvents.26 There

are two views to study the condition of asphaltenes in the crude petroleum systems. The first

opinion considers asphaltenes in terms of solubility that are dissolved in the surrounding

medium, and asphaltene precipitate after the oil solubility falls below a certain condition.27-29

The second one looks at resin as specific stabilizer agents of asphaltene molecules. Recently, the

study of resins with the recognition of their effect on the stability of asphaltenes in petroleum

fluids has been developed.30, 31 The stabilization of crude oil is recognized because of the

association of resins with asphaltenes to form micelles.32 In a micelle, the core is formed from

self-associating of asphaltenes into an aggregate, and resins is adsorbed onto the core to form a

steric shell.33 The asphaltene stabilization depends on the resins/asphaltenes ratio in the crude oil

inside the reservoir.34 The molecular structure of resins is not unique in different part of crude oil

reservoirs. However, they exist as a group of molecules specified by solubility and adsorption

behavior.35, 36 There are many studies on the effect of resins during asphaltene precipitation

process.37-40 The main point of these studies describes the effect of resins on the onset of

asphaltene precipitation.

Until now, the effect of resin on asphaltene deposition and surface properties changes have not

been studied at different pressures. In this work the stabilizing role of resins on asphaltenes

precipitation at reservoir temperature and different pressures is studied. During this experimental

study, synthetic oil (heptol) with different ratios of resins to asphaltenes was used as the oil

Page 4 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

4

model to analyze the conditions for asphaltene precipitation and deposition. A high-pressure

high-temperature (HPHT) PVT cell which was already manufactured45, 46 for asphaltene

precipitation and deposition study was utilized to investigate the mentioned parameters at

reservoir conditions. Slide glasses were used to mimic sandstone surfaces as they are placed in

the PVT cell while their surfaces were monitored carefully using digital camera and the captured

pictures were analyzed by a computer.

AFM (Atomic Force Microscopy) has recently been used to characterize the surface properties

at nano structure level. For instance, in this study, the root mean square (RMS) and mean

roughness were obtained from AFM analysis and the topography of the surfaces treated at

different fluids were monitored carefully. Quantitative measurement of surface roughness is

considered to be a valuable characteristic of the AFM technique. Therefore, this method was

utilized here to find out the surface properties alteration.

For further investigation of resin's effect on asphaltene deposition, and changes of surface

properties, the AFM technique and wettability measurement tests were also utilized.

EXPERIMENTAL SECTION

Materials

There are several methods for asphaltene and resin extraction were mentioned in the literature

(e.g., ASTM D893-69, D2007-80, Modified D2007-80)41, however the utilized methods in this

work are based on the removal of asphaltenes by precipitation using paraffinic solvent (n-

heptane, IP 143/90)42 prior to chromatographic separation of the remaining crude oil on

attapulgite clay and/or silica gel41.

Page 5 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

5

Asphaltenes were extracted from two different Iranian crude oil samples (Kuh-e-Mond and

Bangestan; their structures and composition mentioned in other papers)43, 44, by dissolving in

excess n-heptane with the ratio of 20:1 and then soxhlet method was used for more purification.

Resins were extracted from the deasphalted oil with the column chromatography method.41,48

The malten (deasphalted oil + n-heptane) was adsorbed to a column of silica gel (Merck 35-70

mesh ASTM), then the saturates and aromatics was washed by a solution of 70:30 n-heptane

(Merck, mole fraction purity > 0.990) and toluene (Merck, mole fraction purity > 0.990), and

finally a mixture of acetone (Merck, mole fraction purity > 0.990), dichloromethane (Merck,

mole fraction purity > 0.990) and toluene with the ratio of 40:30:30 was used to extract the resins

from the column. Synthetic oil used in this study was made by mixing n-heptane and toluene

(heptol).

Slide glasses were utilized as the solid surface to mimic the sandstone rock in the reservoir.

The SARA (Saturates, Aromatics, Resins and Asphaltenes) analysis and composition of crude oil

samples are presented in the reported Tables (see the Tables S1 and S2 of the Supporting

Information)

Experimental apparatus

High Pressure, High Temperature (HPHT) Visual Asphaltene Deposition Apparatus

In this study an apparatus, designed in Shiraz University EOR Research Center, was utilized to

visually observe and determine asphaltene deposition at different ratio of resin to asphaltene at

different pressures and temperatures. The schematic of this apparatus is shown in Figure 1 This

apparatus consists of a high pressure cell which is filled by the oil sample. A rotating metal disk

Page 6 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

6

is placed horizontally inside the cell with eight places for fitting slide glasses on it (item number

13 in Figure 1.).

Figure 1. Schematic diagram of the experimental apparatus including (1) peristaltic pump, (2)

distilled water reservoir, (3) computer, (4) CCD camera, (5) microscope, (6) slide glass, (7)

piston cylinder, (8) cold light source, (9) heater, (10) magnetic mixer, (11) high pressure cell,

(12) rotator, (13) metal disk, (14) fan, and (15) magnetic device.

The precipitated asphaltenes which deposit on the slide glasses, captured by a charge couple

device (CCD) camera (IDS, UI-1485LE-C5 HQ, 5.7 megapixels) which is installed on the top of

a microscope (KRÜSS, MBL2000) with an optical resolution up to 480x. A magnetic device

from the outside of the cell could rotate the rotating disk to keep each slide glass in front of the

microscope. A source of cold light installed inside the cell was supplied to lighten the dark

solution without to generate excess heat. According to the operator needs, the images or videos

can be captured with different resolutions. In this study, the captured images were analyzed with

Sigma Scan Pro 5 software. To adjust the cell temperature and pressure, a heater which was

installed outside of the cell and a high-pressure liquid chromatography (HPLC) pump (Agilent

Technologies 1200 series) were used respectively. The tests were carried out at constant

Page 7 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

7

temperature: 363.15 K and four different pressures: P1 = 435.11 psia, P2 = 870.23 psia, P3 =

1450.38 psia, and P4 = 2030.53 psia. A detailed description of the experimental apparatus is

reported elsewhere.45, 46

Experimental procedure

0.40 gram of asphaltene was dissolved in 275 ml of toluene, followed by stirring gently for 20

minutes, using a magnetic stirrer. Then, desired amount of resins, in specific ratios to the

asphaltenes was added to the solution and stirred for another 40 minutes. After one hour, 225 ml

of n-heptane was added to the mixture and the final solution was mixed again for another one

hour. The prepared synthetic oil was injected into the cell, and then it was allowed to reach the

desired temperature (363.15 K). The pressure of the cell was then increased to 2030.53 psia

using the HPLC pump. The solution in the cell was allowed for possible asphaltene deposition on

the slide glasses for a certain period of time. During this process, high resolution images were

captured sequentially. The pressure was then reduced to the second stage (1450.38 psia) at

constant temperature (363.15 K). The solution was stirred to remove all the asphaltene particles

deposited on the slide glasses from the previous step. Then the image capturing was continued

and the same procedure was repeated for this pressures. The asphaltene deposited area and

particle size distribution were measured with the image processing software. After each test, the

slide glasses were removed from the disk for wettability test (contact angle measurement by

DSA100 (KRÜSS)) and AFM analysis. The fluid inside the cell was exited slowly (during

exiting of fluid the position of asphaltene is checked by camera to stay fixed), and then slide

glasses stay inside the cell for 48 hours to get dry completely and taking out carefully to be ready

for next test. Static contact angle measurements with the sessile drop method were recorded and

analyzed at room temperature by DSA100 (KRÜSS)). In this method a liquid drop rests on a

Page 8 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

8

horizontal flat solid surface. (Figure 5) The contact angle is defined as the angle formed by the

intersection of the liquid-solid interface and the liquid-vapor interface (geometrically acquired by

applying a tangent line from the contact point along the liquid-vapor interface in the droplet

profile). While the drop reaches a stationary position in about a second and the measurement

takes place in few minutes after the drop is placed there. The Young's equation is used in the

apparatus software for measuring contact angle. 47

RESULTS AND DISCUSSION

Resin Effects on Asphaltenes Deposition

The amount of deposited asphaltene is the most desired parameter for any asphaltene related

studies.46 Because of errors associated with the slide glass removal from the HPHT cell, this

parameter must be measured in situ, inside the visual cell. In this study the visual HPHT cell was

equipped with the tools needed to find the amount of deposited asphaltene, which has been

explained elsewhere.45, 46

Initially, the asphaltene deposition tests were carried out, without the presence of the resins.

Two different synthetic oils containing asphaltene from two separate oil reservoirs were used for

this experimental study. Table 1 shows the amount of asphaltene deposition area at constant

temperature as the pressure increases for the two different samples. Each asphaltene deposition

area was calculated after 45 minutes. Table 1 shows that the amount of asphaltene deposition

increases as the pressure increases.

Table 1. Area of Kuh-e-Mond (AK)/ Bangestan (AB) asphaltene deposition at 363.15 K and

different pressures without presence of resin.

Page 9 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

9

Pressure (Psia) 435.11 870.23 1450.38 2030.53

Deposition Area µm2 (AK) 1297134 1337256 1463291 1567192

Deposition Area µm2 (AB) 241597 273824 304833 530270

The surface fraction is defined as a fraction of the surface that is occupied by deposited

asphaltene.48 As it shown in Figure 2 that, the asphaltene of Kuh-e-Mond (AK) sample has more

potential to be deposited than the asphaltene of Bangestan (AB) sample. As the figure below

shows at most pressures the surface fraction of AK is almost five times of AB.

Figure 2. Comparison between Kuh-e-Mond Surface fraction occupied by deposited asphaltene

and that of Bangestan versus pressure at 363.15 K.

Figure 3 shows the sample photographs that were taken from the slide glasses inside the visible

HPHT cell, after 45 minutes. The dark particles are aggregated and deposited asphaltene. These

pictures indicate that the surface area of asphaltene deposition is increased as the pressure

increases; also the surface area of Kuh-e-Mond asphaltene deposition is more than Bangestan

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1000 2000

deposited asphaltene

Pressure (psia)

Kuh-e-Mond Sample

Bangestan Sample

Page 10 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

10

sample. The average asphaltene deposition area of the Kuh-e-Mond (heavier crude oil sample)

was 1416218 µm2 which is 4 times greater than Bangestan sample. It clearly indicates that the

Kuh-e-Mond's potential for asphaltene deposition is significantly higher than Bangestan sample.

Besides, (see Table S3 of the Supporting Information) the average diameter of aggregates which

indicates that the AK asphaltene aggregates more than the AB sample, therefore the larger

deposited particles area were formed.

a)

435.11psia 870.23psia 1450.38 psia 2030.53 psia

b)

435.11psia 870.23psia 1450.38 psia 2030.53 psia

Figure 3. Deposited asphaltene a)Kuh-e-Mond, b)Bangestan, at 363.15 K and different

pressures.

In the next stage, the effect of resin on asphaltene deposition of the two crude oil samples with

two different potentials of deposition were investigated. It was already shown, in the previous

sections, that one of these samples has higher potential for asphaltene deposition (Kuh-e-Mond)

compared to the other sample (Bangestan).

Page 11 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

11

In the second part of the experiment, resin was added to the synthetic oil at the specific ratios

to the asphaltenes (R/A). Resin to asphaltene ratios were set at the values of 0.3, 1.5 and 3. The

resin and asphaltene in the synthetic oil samples were extracted from the same crude oil samples.

The results which are presented in the Tables S4 and S5 of the Supporting Information show the

area of asphaltene deposition for Kuh-e-Mond and Bangestan samples with three R/A ratios (0.3,

1.5 and 3.0). Also Figure 4 shows the surface fraction of deposited asphaltene with the same

ratios. The results indicate that the resin in the solution inhibits the asphaltene deposition;

however this behavior is not the same for the both oil samples. The effect of Kuh-e-Mond's resin

(RK) on stabilizing Kuh-e-Mond's asphaltene (AK) is evident in all ratios, as the higher ratio of

resin to asphaltene leads to more asphaltene stability, hence less deposition. The results show as

the amount of resin increases from 0.3 to 1.5 and then to 3.0, the surface fraction was decreased

significantly. On the other hand, resins of Bangestan (RB) do not show the same effect to

decrease the asphaltene precipitation. As it is shown, at resin to asphaltene ratio (RB/AB = 0.3),

asphaltene precipitation does occur as the same as no resins was present. However the results

indicate that RB/AB ratio of 3.0 inhibits asphaltene deposition for Bangestan sample at different

pressures. Figure 4 shows that for the resin to asphaltene ratios with more stabilized asphaltene

condition at low pressure (for example RK/AK=1.5 and RK/AK=3.0), as the pressure increases

the stability of asphaltene decreases, and this is related to the theory of forming asphaltene and

resin in to micelle form.5, 26

Asphaltenes are disposed to self-associate and form micelles and resins are known as peptizing

agents that adsorb to these micelles, make a steric shell and play the role of surfactants to

stabilize the asphaltenes.35

Page 12 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

12

Figure 4. Comparison between Kuh-e-Mond Surface fraction occupied by deposited asphaltene

and that of Bangestan (with and without presence of resin) versus pressure at 363.15 K.

The results show that the pressure changes have the same effect on both samples. For example,

the highest deposition has been occurred at 2030.53psia.

A notable effect of resins on the asphaltenes is to minimize the asphaltene aggregates

compared to the cases without resins. The results obtained from the image processing software

showed, the increase in the amount of resins leads to the smaller aggregates of asphaltenes which

is in agreement with the previous studies in this regard .39 Vapor pressure osmometry (VPO)48

and small angle X ray scattering36 measurements have been used in the past where it was

concluded that presence of resins significantly decreased the size of asphaltene aggregates. These

results have shown the anti-flocculants action of resins.49-51

0

0.2

0.4

0.6

0.8

1

0 500 1000 1500 2000 2500

depo

site

d a

spha

lten

e in

pre

senc

e of

res

in

Pressure (psia)

RB/AB=0.3 RK/AK=0.3

RB/AB=1.5 RK/AK=1.5

RB/AB=3.0 RK/AK=3.0

AB AK

Page 13 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

13

Also it must be noted that the effect of different resins from different sources (RB and RK) on

the aggregate size reduction for asphaltenes are not the same. The results shown in Table S6

compared to Table S3 of the supporting information indicate that RK is more effective than RB

to minimize the size of asphaltene aggregates.

Surface Analysis

To investigate the changes in surface properties, the slide glasses were taken out of the cell

after each test for wettability tests using contact angle measurement and performing AFM tests.

For comparing the surfaces, four aged slide glasses in AK, AB, RK and RB were chosen for this

investigation. The soaking period was 30 days and the results of contact angle measurements are

presented in Table 2.

Table 2. Contact angle data of the aged slide glasses in Resin, Asphaltene, and different

resin/asphaltene ratios.

Contact angle Contact angle

Aged AB 83.6 Aged AK 88

Aged RB 93.7 Aged RK 92

(RB/AB)=0.3 70 (RK/AK)=0.3 69

(RB/AB)=1.5 70 (RK/AK)=1.5 71

(RB/AB)=3 73 (RK/AK)=3 70

The results well indicates the effects of asphaltenes and resins in the oil on the wettability of the

solid surfaces. Asphatenes could alter the surface to be more oil wet as it has been already

reported in many occasions. If the resins are the only heavy oil component, then the surfaces

become even more oil wet. However, if the oil model contains both, asphaltene and resin, then

the treated surfaces in this type of oil tends to be more water-wet. As Figure 5 shows the droplet

of water on asphaltene surface has wider angle in contact with immiscible fluid (air) than the

asphaltene in the presence of resin surface. These results then confirm the previous findings of

Page 14 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

14

inhibiting effects of the resins for asphaltene deposition. Therefore, compared to the aged slide

glasses in the asphaltene, less asphaltene was deposited on the surfaces in the presence of resins,

keeping the surfaces to be more water wet.

a) b)

Figure 5. Comparison between wettability of surfaces a) asphaltene and b) asphaltene in

presence of resin.

AFM (Atomic Force Microscopy) Tests

The surfaces of the treated and fresh slide glasses were scanned using AFM and the nano-scale

topography images were studied carefully to find any surface properties changes.45 Several

different parameters such as height distribution and roughness parameters could be measured

from the AFM images, on the basis of a specific area. To evaluate and compare the quality of the

surfaces, several parameters have to be collected from the AFM images, such as Sz, Sa, Sq, Sds

and Sdr, according to eqs 1, 2, 3, 4 and 5 respectively. The summits and alleys are defined as the

points that are higher than all eight neighboring points.52 Note that the points on the edge of the

area are not considered.

Sz =∑ |�������� |�∑ |����������� |���� �

Sa =∬ |���, ������|�

Sq =�∬ ����, ���������

Page 15 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

15

Sds =� !"�#$%����

&#��

Sdr = �'��� #�( #%�)�&#���–�+#$ (�)�$,��&#���

+#$ (�)�$,��&#��

The AFM topography images with height images (on the basis of the path drawn) and the

aforementioned parameters are presented in Figure 6, Table 3, and Figure S1 (Supporting

Information) respectively.

The results show significant change in the topography of the surfaces after the slide glasses

were aged in different oil models. The fresh slide glass has a smooth surface with a mean

roughness (Sa) of 1.36 nm. Also the parameter Sdr which is called as the developed interfacial

area ratio, is close to zero (Sdr=0.09) which indicates the smoothness of the fresh surfaces.

As the results show, surface topography was changed after the slide glasses were treated with

the oil; however the changes are significant for the asphaltenes deposition when no resin is

present. From the AFM 3D images, it is depicted that both asphaltene samples, AK and AB, have

formed deep valleys and high summits. The path drawn in each 2D image shows the differences

between topography of asphaltenes and resins. For example, the change of altitude in AB is from

100 to about 800 nm while it the case of its native resin, RB, it is about 3 to 8 nm. The

parameters Sa and Sdr for AB treated surfaces are 119 nm and 20.5 % respectively. The same

parameters in the case of RB are 2.12 nm and 0.05 %. These quantitative results show that a

smooth layer has been formed by the resins on the treated surfaces. Furthermore, comparing the

AFM images for asphaltene and resin, it is seen that the asphaltene deposited particles are clearly

shown there while the resin deposition is not evident. This is attributed to the tendency of

asphaltenes to aggregate and form mega scale asphaltene particles as reported in the literature.5, 6,

10 Also the high deposition potential of asphaltenes and their tendency to adhere to the surfaces

compared to resins must be considered to evaluate this phenomenon.

Page 16 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

16

a)

b)

c)

Figure 6. 3D and 2D AFM images of asphaltene deposition on slide glasses: (a), fresh slide glass

(b) RB/AB=1.5(c) RK/AK=1.5

Table 3. Calculated AFM parameters for different samples.

Page 17 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

17

Substrates Sz (nm) Sa (nm) Sdr (%) Sq (nm) Sds (µm-2)

Fresh slide glass 13.8 1.36 0.01 1.82 11

Aged AB 946 119 20.5 168 5.38

Aged AK 379 41.8 12.1 56.6 6.31

Aged RB 40.4 2.12 0.05 4.11 12

Aged RK 51.1 2.79 0.09 4.36 11.2

Aged (RB/AB) = 1.5 862 98.6 13.7 149 2.53

Aged (RK/AK) = 1.5 603 74.8 8.2 105 1.88

The asphaltenes and resins of the two different samples behave exclusively the same. The effects

of added resins to their native asphaltenes were almost similar to each other. In both cases, the

topography parameters presented in Table 3 show that the roughness of surface is decreased

when resins were added with R/A of 1.5 compared to the aged slide glasses in the oil sample

without the resins. For instance, the parameters Sa and Sdr for the solution of RB and AB with

RB/AB of 1.5, are 98.6 nm and 13.70 % which show more smooth surfaces than the case aged

with AB. These quantitative results and examination of the images clearly indicate the effect of

resins on the asphaltene deposition and hence the surface topography.

CONCLUSION

In the present study, a HPHT PVT cell was used to investigate the asphaltene deposition

behavior at the presence of resins with different ratios at reservoir temperature and relatively

high pressures. To recognize the change of surface properties, the wettability measurement by

contact angle and AFM techniques were utilized. The results show, as the ratio of resin to

asphaltene (R/A) increases, more stable asphaltene conditions are achieved However, as the

pressure increases the asphaltene deposition increases significantly. It was found that the effect

of resin on the stability of asphaltene is more evident in the oil sample with high potential of

asphaltene deposition compared to the oil sample with low potential of deposition at the same

Page 18 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

18

resin to asphaltene ratios. The effect of resin on the stability of asphaltene decreases as the

pressure increases, and this is more obvious at higher ratio of resin to asphaltene. Since different

results were found for asphaltene inhibition in different oil samples when the resin is present, it

is concluded that this phenomenon depends on the asphaltenes structures as well. Finally the

previous findings were confirmed by comparing the results with contact angle measurement and

AFM analysis which also suggested the significant effects of resins on asphaltene deposition

hence the surface property changes.

ASSOCIATED CONTENT

S Supporting Information

Additional tables and data as described in the text. (Crude oil composition, Deposition area)

This material

is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION

Corresponding Author

*E-mail: shahab@sharif.ir. Tel./Fax: +98 21-66166411

Present Addresses

†Sharif University of Technology, Tehran, Iran.

Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENT

Page 19 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

19

We would like to express our special thanks of gratitude to Dr. Dehghani and Dr. Esmaeil Poor

for their guidance on resins extraction. We are also grateful to Ali Tohidi for his efforts to build

the HP-HT Visual Asphaltene Deposition Apparatus

ABBREVIATIONS

PVT, pressure volume temperature; AFM, atomic force microscopy; HPHT, high-pressure high-

temperature; RB, resin of Bangestan; RK, resin of Kuh-e-Mond; AB, asphaltene of Bangestan;

AK, asphaltene of Kuh-e-Mond.

REFERENCES

1. Aske, N.; Kallevik, H.; Sjöblom, J., Determination of saturate, aromatic, resin, and asphaltenic (SARA) components in crude oils by means of infrared and near-infrared spectroscopy. Energy & Fuels 2001, 15, (5), 1304-1312. 2. Pelet, R.; Behar, F.; Monin, J., Resins and asphaltenes in the generation and migration of petroleum. Organic Geochemistry 1986, 10, (1), 481-498. 3. Hua, Y.; Angle, C. W., Brewster Angle Microscopy of Langmuir Films of Athabasca Bitumens, n-C5 Asphaltenes, and SAGD Bitumen during Pressure–Area Hysteresis. Langmuir 2012, 29, (1), 244-263. 4. McCain, W., The properties of petroleum fluids. PennWell Books: 1990. 5. Goual, L.; Firoozabadi, A., Effect of resins and DBSA on asphaltene precipitation from petroleum fluids. AIChE journal 2004, 50, (2), 470-479. 6. Merino-Garcia, D.; Andersen, S. I., Thermodynamic characterization of asphaltene-resin interaction by microcalorimetry. Langmuir 2004, 20, (11), 4559-4565. 7. Rogel, E., Asphaltene aggregation: A molecular thermodynamic approach. Langmuir 2002, 18, (5), 1928-1937. 8. Buenrostro-Gonzalez, E.; Groenzin, H.; Lira-Galeana, C.; Mullins, O. C., The overriding chemical principles that define asphaltenes. Energy & fuels 2001, 15, (4), 972-978. 9. Stachowiak, C.; Viguié, J.-R.; Grolier, J.-P. E.; Rogalski, M., Effect of n-alkanes on asphaltene structuring in petroleum oils. Langmuir 2005, 21, (11), 4824-4829. 10. Long, R. B., The concept of asphaltenes. Chemistry of Asphaltenes 1981, 195, 17-27. 11. Liu, D.; Li, Z.; Fu, Y.; Zhang, Y.; Gao, P.; Dai, C.; Zheng, K., Investigation on asphaltene structures during venezuelan heavy oil hydrocracking under various hydrogen pressure. Energy & Fuels 2013. 12. Hashmi, S. M.; Quintiliano, L. A.; Firoozabadi, A., Polymeric Dispersants Delay Sedimentation in Colloidal Asphaltene Suspensions. Langmuir 2010, 26, (11), 8021-8029. 13. Sun, Y.-d.; Yang, C.-h.; Zhao, H.; Shan, H.-h.; Shen, B.-x., Influence of asphaltene on the residue hydrotreating reaction. Energy & fuels 2010, 24, (9), 5008-5011. 14. Strausz, O. P.; Mojelsky, T. W.; Lown, E. M., The molecular structure of asphaltene: an unfolding story. Fuel 1992, 71, (12), 1355-1363.

Page 20 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

20

15. Al-Sahhaf, T. A.; Fahim, M. A.; Elkilani, A. S., Retardation of asphaltene precipitation by addition of toluene, resins, deasphalted oil and surfactants. Fluid phase equilibria 2002, 194, 1045-1057. 16. Sanjay, M.; Simanta, B.; Kulwant, S., Paraffin problems in crude oil production and transportation: a review. Old Production & Facilities 1995, 10, (1), 50-54. 17. Hammami, A.; Ratulowski, J., Precipitation and deposition of asphaltenes in production systems: A flow assurance overview. In Asphaltenes, Heavy Oils, and Petroleomics, Springer: 2007; pp 617-660. 18. Izquierdo, A.; Rivas, O. In A global approach to asphaltene deposition problems, International Symposium on Oilfield Chemistry, 1997; 1997. 19. Sheu, E. Y.; Mullins, O. C., Asphaltenes: fundamentals and applications. Plenum Publishing Corporation: 1995. 20. Hoepfner, M. P.; Vilas Bôas Fávero, C.; Haji-Akbari, N.; Fogler, H. S., The Fractal Aggregation of Asphaltenes. Langmuir 2013. 21. Akbarzade, K.; Hammany, A.; Harat, A., Asphaltenes: problems and prospects. Oil and Gas Review 2007, 28-53. 22. Hammami, A.; Phelps, C. H.; Monger-McClure, T.; Little, T., Asphaltene precipitation from live oils: An experimental investigation of onset conditions and reversibility. Energy &

Fuels 2000, 14, (1), 14-18. 23. Speight, J. G., The chemical and physical structure of petroleum: effects on recovery operations. Journal of Petroleum Science and Engineering 1999, 22, (1), 3-15. 24. Wang, J.; Buckley, J.; Burke, N.; Creek, J., A Practical Method for Anticipating Asphaltene Problems (includes associated papers 104235 and 105396). Old Production &

Facilities 2004, 19, (3), 152-160. 25. Nielsen, B. B.; Svrcek, W. Y.; Mehrotra, A. K., Effects of temperature and pressure on asphaltene particle size distributions in crude oils diluted with n-pentane. Industrial &

engineering chemistry research 1994, 33, (5), 1324-1330. 26. Koots, J. A.; Speight, J. G., Relation of petroleum resins to asphaltenes. Fuel 1975, 54, (3), 179-184. 27. Hirschberg, A.; DeJong, L.; Schipper, B.; Meijer, J., Influence of temperature and pressure on asphaltene flocculation. Old SPE Journal 1984, 24, (3), 283-293. 28. Andersen, S. I., DIBSOLUTION OF SOLID BOBCAN ASPHALTENES IN MIXED SOLVENTS. Fuel science & technology international 1994, 12, (11-12), 1551-1577. 29. Li, S.; Liu, C.; Que, G.; Liang, W.; Zhu, Y., A study of the interactions responsible for colloidal structures in petroleum residua. Fuel 1997, 76, (14), 1459-1463. 30. Sedghi, M.; Goual, L., Role of Resins on Asphaltene Stability†. Energy & Fuels 2009, 24, (4), 2275-2280. 31. Pereira, J. C.; López, I.; Salas, R.; Silva, F.; Fernández, C.; Urbina, C.; López, J. C., Resins: The molecules responsible for the stability/instability phenomena of asphaltenes. Energy & fuels 2007, 21, (3), 1317-1321. 32. Swanson, J. M., A Contribution to the Physical Chemistry of the Asphalts. The Journal of Physical Chemistry 1942, 46, (1), 141-150. 33. Firoozabadi, A., Thermodynamics of hydrocarbon reservoirs. McGraw-Hill New York: 1999.

Page 21 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

21

34. Carnahan, N. F.; Salager, J.-L.; Antón, R.; Dávila, A., Properties of resins extracted from Boscan crude oil and their effect on the stability of asphaltenes in Boscan and Hamaca crude oils. Energy & Fuels 1999, 13, (2), 309-314. 35. Seki, H.; Kumata, F., Structural change of petroleum asphaltenes and resins by hydrodemetallization. Energy & fuels 2000, 14, (5), 980-985. 36. Bardon, C.; Barre, L.; Espinat, D.; Guille, V.; Li, M. H.; Lambard, J.; Ravey, J.; Rosenberg, E.; Zemb, T., The colloidal structure of crude oils and suspensions of asphaltenes and resins. Fuel science & technology international 1996, 14, (1-2), 203-242. 37. Acevedo, S.; Escobar, G.; Gutiérrez, L. B.; Rivas, H.; Gutiérrez, X., Interfacial rheological studies of extra-heavy crude oils and asphaltenes: Role of the dispersion effect of resins in the adsorption of asphaltenes at the interface of water-in-crude oil emulsions. Colloids and Surfaces A: Physicochemical and Engineering Aspects 1993, 71, (1), 65-71. 38. Murgich, J.; Rodríguez, J.; Aray, Y., Molecular recognition and molecular mechanics of micelles of some model asphaltenes and resins. Energy & fuels 1996, 10, (1), 68-76. 39. León, O.; Contreras, E.; Rogel, E.; Dambakli, G.; Acevedo, S.; Carbognani, L.; Espidel, J., Adsorption of native resins on asphaltene particles: a correlation between adsorption and activity. Langmuir 2002, 18, (13), 5106-5112. 40. Mousavi-Dehghani, S.; Riazi, M.; Vafaie-Sefti, M.; Mansoori, G., An analysis of methods for determination of onsets of asphaltene phase separations. Journal of Petroleum Science and Engineering 2004, 42, (2), 145-156. 41. Miller, R., Hydrocarbon Class Fractionation with Bonded-Phase Liquid Chromatography. Anal. Chem. 1982, 54, (11), 1742-1746. 42. Asphaltene (n-heptane insolubles) in petroleum products, Standards for petroleum and its products, Standard No. IP 143/90, Institute of Petroleum, London, U.K., 143.1-143.7, 1985. 43. Amin, J. S.; Nikooee, E.; Ghatee, M.; Ayatollahi, S.; Alamdari, A.; Sedghamiz, T., Investigating the effect of different asphaltene structures on surface topography and wettability alteration. Applied Surface Science 2011, 257, (20), 8341-8349. 44. Ghatee, M. H.; Hemmateenejad, B.; Sedghamiz, T.; Khosousi, T.; Ayatollahi, S.; Seiedi, O.; Sayyad Amin, J., Multivariate curve resolution alternating least-squares as a tool for analyzing crude oil extracted asphaltene samples. Energy & Fuels 2012, 26, (9), 5663-5671. 45. Zanganeh, P.; Ayatollahi, S.; Alamdari, A.; Zolghadr, A.; Dashti, H.; Kord, S., Asphaltene Deposition during CO2 Injection and Pressure Depletion: A Visual Study. Energy &

Fuels 2012, 26, (2), 1412-1419. 46. Sayyad Amin, J.; Alamdari, A.; Mehranbod, N.; Ayatollahi, S.; Nikooee, E., Prediction of asphaltene precipitation: Learning from data at different conditions. Energy & Fuels 2010, 24, (7), 4046-4053. 47. Tadmor, R.; Yadav, P.; As-placed contact angles for sessile drops. Journal of Colloid and Inerface Scienc 2008, 317, 241–246 48. Yarranton, H. W.; Alboudwarej, H.; Jakher, R., Investigation of asphaltene association with vapor pressure osmometry and interfacial tension measurements. Industrial & engineering chemistry research 2000, 39, (8), 2916-2924. 49. Spiecker, P. M.; Gawrys, K. L.; Trail, C. B.; Kilpatrick, P. K., Effects of petroleum resins on asphaltene aggregation and water-in-oil emulsion formation. Colloids and surfaces A: Physicochemical and engineering aspects 2003, 220, (1), 9-27.

Page 22 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

22

50. Espinat, D.; Ravey, J. In Colloidal structure of asphaltene solutions and heavy-oil fractions studied by small-angle neutron and X-ray scattering, SPE International Symposium on Oilfield Chemistry, 1993; 1993. 51. Barre, L.; Espinat, D.; Rosenberg, E.; Scarsella, M., Colloidal Structure of Heavy Crudes and Asphaltene Soltutions. Oil & Gas Science and Technology 1997, 52, (2), 161-175. 52. Seiedi, O.; Rahbar, M.; Nabipour, M.; Emadi, M. A.; Ghatee, M. H.; Ayatollahi, S., Atomic force microscopy (AFM) investigation on the surfactant wettability alteration mechanism of aged mica mineral surfaces. Energy & Fuels 2010, 25, (1), 183-188.

Page 23 of 23

ACS Paragon Plus Environment

Energy & Fuels

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960