Effect of Carbon Steel Corrosion on Asphaltene Deposition - Energy

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Effect of Carbon Steel Corrosion on Asphaltene Deposition Mohammad Tavakkoli, Chi-An Sung, Jun Kuang, Andrew Chen, Jeremy Hu, and Francisco M. Vargas Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b03238 • Publication Date (Web): 17 Dec 2018 Downloaded from http://pubs.acs.org on December 21, 2018

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Effect of Carbon Steel Corrosion on Asphaltene Deposition Mohammad Tavakkoli1, Chi-An Sung2, Jun Kuang1, 2, Andrew Chen2, Jeremy Hu2, and Francisco M. Vargas1, 2 1 2

ENNOVA LLC, 4100 Greenbriar Dr., Suite 230, Stafford, Texas, 77477.

Rice University, Department of Chemical and Biomolecular Engineering, 6100 Main St., MS-362, Houston, Texas, 77005.

Authors Email Address: [email protected], [email protected], [email protected], [email protected], [email protected], and [email protected] Corresponding Author: email - [email protected], Phone - +1 (713) 348-2384 Abstract In this work, the effect of carbon steel corrosion on asphaltene deposition tendency was investigated. A new experimental setup, consisting of a multi-section column made of polytetrafluoroethylene (PTFE) was built and packed with carbon steel spheres, which then was used to quantify the deposition of asphaltenes under different conditions. It was found that in the presence of iron ions in a brine-in-oil emulsion, the amount of deposited material upon addition of an asphaltene precipitant, such as n-heptane, was significantly higher than in the case of iron-free brine. In addition, it was observed that asphaltenes have a higher tendency to deposit on the rust-covered metallic surfaces compared to the clean and smooth carbon steel spheres. Also, increasing the surface roughness can lead to a higher asphaltene deposition rate. To reduce the extent of asphaltene deposition induced by the tube corrosion, a chelating agent, ethylenediaminetetraacetic acid (EDTA), was added to sequestrate the iron ions. The results obtained showed that the EDTA is able to mitigate the extent of corrosion-induced asphaltene deposition on metallic surfaces. Consequently, by addressing the corrosion problem, asphaltene deposition may actually subside. The deposition tests also revealed a surprising result: even 1 ACS Paragon Plus Environment

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though the EDTA reduced the amount of asphaltene deposition on carbon steel spheres, it significantly increased the amount of deposit collected on the PTFE surface. With these results, we conclude that corrosion and asphaltene deposition are two problems that must be concurrently investigated and that strategies for their mitigation should account for the interactions between chemicals in the bulk phase and also with the exposed surfaces. Keywords: Asphaltene Deposition, Pipeline Corrosion, Mitigation Strategy.

1. Introduction Asphaltene deposition can considerably affect the oil production rate by reduction of reservoir permeability and porosity, alteration of wettability, and plugging of wellbore and production equipment. These phenomena lead to significant costs for the oil industry. Costs from the production loss could be as high as 1 MM USD per day, and from the remediation, such as removal of deposited materials, could be up to 3 MM USD1. Therefore, it is of great importance for the oil industry to prevent or mitigate the asphaltene deposition problem during oil production. It is possible that several flow assurance problems simultaneously occur during oil production. However, the solution strategy is normally addressed for an individual problem and the interrelation between different problems is typically ignored. It has been identified that iron ions in crude oils could promote asphaltene sludging and aggravate asphaltene deposition problems2–8. Most of the pipelines used for oil transportation are made of carbon steel, which can be deteriorated by salts, gases, or any acidic components coming from the reservoir. Iron ions are then released into the fluid phase as a result of the pipeline corrosion. Iron ions are also present in the oil phase due to contact of the reservoir fluid with the formation water and/or the seawater injected to increase oil recovery. According to a study by Sung et al.9, the effect of 2 ACS Paragon Plus Environment

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ferric ions on asphaltene instability, in both model oil and real crude oil systems, is more significant than the effects of other variables such as other cations, emulsified water, salinity, acidic pH, and metallic ion valence. However, there is limited knowledge on the effect of iron ions on asphaltene deposition tendency. In addition, the effect of rust (iron oxide) accumulated on pipeline surfaces as well as the effect of surface roughness of the corroded pipelines on asphaltene deposition tendency needs to be investigated. Also, to the best of our knowledge, no study has been conducted to mitigate the corrosion-induced asphaltene deposition problem. Researchers have developed various experimental setups, such as the metal capillary tube, Taylor-Couette device, and Quartz Crystal Microbalance with Dissipation (QCM-D) to study asphaltene deposition in pipe flows in the laboratory10–12. However, there are disadvantages associated with each technique. A metal capillary tube is a popular and reliable technique for studying asphaltene deposition. However, because the capillary tube experiment is done near the onset of asphaltene precipitation, it requires a large amount of oil sample and the precipitated and deposited material might not be representative of the entire asphaltene distribution. Deposition experiments using a Taylor-Couette device are very costly and a large quantity of the crude oil sample is needed per test. In addition, the flow in a Taylor-Couette device does not represent a pipeline flow, which is typically Poiseiulle flow, and a mathematical modeling must be utilized to translate the results obtained from the Taylor-Couette device to pipeline flow. QCM-D experiments are mostly limited to the adsorption of asphaltenes and it is not straightforward to distinguish between adsorption and deposition of asphaltenes with this technique. More information on the advantages and disadvantages of different experimental techniques to investigate asphaltene deposition has been provided in reference 13.

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In this work, a new experimental setup, consisting of a multi-section PTFE column packed with carbon steel spheres, is utilized to study asphaltene deposition on metallic surfaces. The effect of pipeline corrosion on asphaltene deposition is studied using this new experimental technique. In addition, a mitigation strategy is introduced to minimize the adverse effect of the corrosion on asphaltene deposition tendency.

2. Experimental Procedure 2.1. Sample Preparation In this study, the experiments were conducted at 1 bar and 23 °C using a model oil system. To prepare the model oil, asphaltenes were separated from the crude oil P using normal pentane as the precipitant and then were dissolved in toluene. Asphaltene concentration of 5 wt% was used for the model oil system. Deposition experiments were done by mixing the prepared model oil with the desired amount of normal heptane. To study the effect of ferric ions in the oil bulk phase on asphaltene deposition, an emulsion system was prepared prior to mix with n-heptane. The emulsion was prepared by slowly adding the desired amount of FeCl3 solution to the model oil while the mixture was homogenized with a SCILOGEX D-160 homogenizer at approximately 20,000 rpm for 10 minutes. The FeCl3 solution containing 20,000 ppm ferric ions was prepared by dissolving anhydrous ferric chloride in deionized water. Deionized water was obtained from a Millipore Direct–Q3 water purification system. The preparation of the emulsion was conducted at ambient conditions. The methodology for water in oil emulsion preparation was taken from Tavakkoli et al.14


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2.2. Asphaltene Deposition Tests An experimental setup, consisting of a multi-section PTFE column packed with 10101020 grade carbon steel spheres, depicted by Figure 1, was utilized in this work to study asphaltene deposition on metallic surfaces. This setup was originally designed by Favero et al.15 and was then modified by Melendez16. The metallic surfaces of carbon steel spheres are available for asphaltenes to deposit on. The PTFE was chosen for the column material because the tendency of asphaltenes to adhere to the PTFE is very low17,18. Therefore, the deposition mainly forms on the carbon steel spheres and analysis of the deposited asphaltenes is straightforward. The PTFE column used in this study was made of two sections and spheres in these sections were separated using a molded PTFE Mesh. Two syringe pumps (Harvard Apparatus Pump 11 Elite and Chemyx Fusion 100) with Hamilton Gaslight Syringes were used to inject the oil and precipitant into the column. The Perfluoroalkoxy (PFA) tubing was used to transfer the oil, precipitant, or the mixture of oil and precipitant between different segments of the setup.


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PTFE Column with carbon steel spheres

Syringe pump Model oil / Emulsion Effluent

T-junction immersed in an ultrasonic water bath

Syringe pump Precipitant (n-heptane)

Figure 1. Schematic of the multi-section packed column setup used in this study for asphaltene deposition study16. To conduct an experiment using the deposition test apparatus, one syringe was charged with the oil or emulsion, and the other syringe was charged with the precipitant (n-heptane was used in this study). The pumps were programmed based on the flow rates of the injected fluids and then were started simultaneously. After turning on the pumps, the fluids flowed inside the PFA tubing towards the T-junction immersed in an ultrasonic bath at 40 kHz. The bath used in this study was Bransonic, CPX1800H. The temperature of the ultrasonic bath was kept constant at around 23 °C using a copper cooling coil connected to an external water bath. After the oil/emulsion and n-heptane were mixed in the T-junction, the mixture flowed from the bottom of the column (inlet) to the top of the column (outlet) and the effluent at the outlet was collected for further analysis. For the experiments with water in oil emulsion, a stir bar was placed inside 6 ACS Paragon Plus Environment

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the syringe containing the emulsion and the syringe was placed on top of a stirrer in order to have a continuous mixing and a stable emulsion during the experiment. At the end of each experiment, the column was first drained by gravity. Then, a very light flow of nitrogen was used to force any liquid trapped between the spheres to leave the column. This step is very delicate since a high pressure of nitrogen might remove the deposited asphaltenes on spheres. After the draining process, the column was disassembled. The spheres were then collected and weighed. The difference in mass of the spheres before and after the experiment shows the mass of asphaltenes deposited on the spheres metallic surfaces. This new asphaltene deposition setup has several advantages over the metal capillary tube system. First, the column is packed with carbon steel spheres to increase the surface area for asphaltenes to deposit on, which in turn decreases the length of the column. Moreover, the packed column consists of multiple sections and the amount of deposition for each section is measured independently. Thus, the deposition profile can be obtained easily using this apparatus. Also, the packed bed column deposition apparatus requires a small amount of oil sample to investigate the deposition phenomena. Around 20 mL of oil sample was used for each deposition experiment performed in this work. Finally, spheres made of different materials can be used in the packed column setup in order to study the tendency of asphaltenes to deposit on various materials. In this work, corroded carbon steel spheres were used to investigate the effect of corrosion on asphaltene deposition. Even though the current apparatus operates at ambient conditions, the experimental methodology can be extended to high pressure-high temperature conditions. The current design of the packed bed column to study asphaltene deposition still needs future improvements to address the following limitations: 1) The setup has not been tested to


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simulate the deposition process under turbulent flow regimes; 2) The current deposition is driven by the addition of precipitants, whereas asphaltene deposition in the production tubing is induced by pressure depletion; 3) With the current procedure, the amount of deposition is measured using the gravimetric technique. With this technique, the mass of deposited materials should be above 50 mg in order to achieve reproducible experimental results. As a future improvement, the gravimetric technique can be replaced by spectroscopic analysis for more accurate measurement of the deposited materials. Table 1 reports the experimental conditions used in this work to study asphaltene deposition using the packed column setup. To ensure the repeatability of the experimental data, each experiment has been repeated at least twice and the average value and the corresponding standard deviation are reported. The experimental error reported in this work is in the range of the error for the packed bed column deposition experiments reported by Kuang et al.19,20. Table 1. Experimental conditions used for asphaltene deposition tests. Experimental Condition Asphaltene concentration in the model oil Oil/precipitant volume ratio Duration of the experiment Flow rate Temperature Pressure Sphere radius Total surface area of the spheres packed in the column Pore volume of the packed column


Value 5 wt% 30/70 6h 9 cc/h 23 °C 1 bar 0.12 cm 139.2 cm2 5.6 cm3

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3. Results and Discussion 3.1. Asphaltene Deposition on Carbon Steel Spheres 3.1.1. No aqueous phase In this study, the model oil with 5 wt% asphaltene concentration was co-injected with nheptane to investigate the amount of asphaltenes deposited on metallic spheres. Table 2 presents the amount of asphaltenes deposited on the spheres and the PTFE column, without the presence of an aqueous phase in the system. One can see from Table 2 that the amount of deposition on the spheres in the bottom section is more than on the spheres in the top section of the column. This means that the deposition rate is higher at the inlet of the column, which is in line with some of the experimental data available in the literature obtained from the capillary tube tests12. In addition, the amount of asphaltene deposition on the spheres is more than the PTFE column. Table 2. Amount of asphaltene deposition on the spheres and the PTFE column for the experiment without the presence of an aqueous phase

Bottom Top Total

Deposited asphaltenes, % of total infused asphaltenes Spheres PTFE Column 17.4 ± 0.2 2.7 ± 0.1 6.0 ± 1.2 0.9 ± 0.4 23.4 ± 1.4 3.6 ± 0.5

During the deposition experiment, a sample of the effluent was collected every hour. This sample contains some precipitated asphaltenes which did not deposit on the spheres. These asphaltenes are called “Aggregated Asphaltenes” in this work. From the total infused asphaltenes, some precipitate out of the system and some remain in the solution. From the precipitated asphaltenes, some deposit on spheres and some are produced in the effluent, which are called the aggregated asphaltenes. The collected effluent samples were then centrifuged to settle the aggregated asphaltenes. The supernatant liquid, which contains dissolved asphaltenes 9 ACS Paragon Plus Environment

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in toluene, was removed after centrifugation and the mass of aggregated asphaltenes was measured. Figure 2 shows the mass of aggregated asphaltenes in the effluent versus the injected pore volume (injected P.V.). It can be seen from this figure that the mass of aggregated asphaltenes has an increasing trend with the injected P.V. This means that the precipitated asphaltenes entering the column at a later stage of the test have less tendency to deposit on the spheres compared to the asphaltenes entering the column at an earlier stage. We believe that once iron spheres surfaces are covered by asphaltenes, the rate of asphaltene deposition on spheres decreases. We speculate that this is related to the higher interaction energy between asphaltenes and the iron spheres compared to the interaction energy between asphaltenes. Also, once the spheres are covered with asphaltenes, then there would be no significant difference between asphaltene-asphaltene interaction in the bulk phase and asphaltene-asphaltene interaction on the surface of the spheres. However, because the size of asphaltenes in the bulk phase is very small, they provide a very large surface area compared to the deposited asphaltenes, and therefore, the asphaltenes in the bulk phase prefer to attach to each other and aggregate more, and as a result, deposit on the spheres with a lower rate. It is also important to mention that asphaltene aggregation and deposition are two competing phenomena. As reported by Vargas et al.21, once the rate of asphaltene aggregation in the bulk phase increases, the rate of asphaltene deposition decreases.


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Aggregated asphaltenes in the outlet (wt% of the effluent)

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Figure 2. Aggregated asphaltenes collected from the effluent vs. the injected P.V. The experiment was performed without the presence of an aqueous phase in the system. The ASD (Average Standard Deviation) is 1.01%. 3.1.2. Effect of emulsified water on asphaltene deposition To investigate the effect of emulsified water on asphaltene deposition tendency, water in oil emulsion was prepared by mixing the model oil with deionized water obtained from a Millipore Direct–Q3 water purification system. The amount of water in the emulsion was 30 volume percent. Table 3 reports the amounts of deposited asphaltenes on the spheres and the column, with and without the presence of emulsified water. Based on the obtained results, the total amount of deposited asphaltenes in the presence of emulsified water is slightly less than the amount of deposited asphaltenes when there is no aqueous phase in the system.


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Table 3. Amount of asphaltene deposition on the spheres and the PTFE column for the experiments with and without the presence of emulsified water

Spheres PTFE column Total

Deposited asphaltenes, % of total infused asphaltenes No aqueous phase With emulsified water 23.4 ± 1.4 24.9 ± 1.5 3.6 ± 0.5 0.8 ± 0.1 27.0 ± 1.9 25.7 ± 1.6

Figure 3 depicts the amounts of aggregated asphaltenes collected from the effluent in the experiments with and without the presence of emulsified water. It can be seen that the amount of aggregated asphaltenes in the presence of emulsified water is in overall more than the system without the presence of emulsified water. Aslan et al.22 investigated the effect of water on asphaltene deposition using a stainless steel tubing. They concluded that water evidently delays asphaltene deposition process. Water interacts with the heteroatoms in asphaltene structures by hydrogen bonding, which may make asphaltenes transfer from a hydrophobic to hydrophilic state22. The stainless steel surface is more hydrophobic22–24, and therefore, asphaltene deposition could be delayed by the presence of water and more asphaltene aggregates can be collected from the effluent.


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No aqueous phase With emulsified water

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Figure 3. Aggregated asphaltenes collected from the effluent vs. the injected P.V. The ASD is 1.01% and 0.73% for “no aqueous phase” and “with emulsified water” experiments, respectively. 3.1.3. Effect of ferric ions in the bulk phase on asphaltene deposition tendency To study the effect of ferric ions on asphaltene deposition, an emulsion was prepared by mixing the model oil and FeCl3 solution containing 20,000 ppm ferric ions concentration. The amount of FeCl3 solution in the emulsion was 30 volume percent. Table 4 reports the amounts of deposited materials on the spheres and the PTFE column for the test without an aqueous phase and the experiment with the presence of FeCl3 solution. The amount of deposited materials for the experiment with the presence of FeCl3 solution is much higher than the test without the presence of an aqueous phase. Wang et al.25 also reported the same conclusion. However, the deposited material contains both asphaltenes and ferric ions and to obtain the amount of pure asphaltenes, ferric ions should be removed from the deposited materials. To do so, the spheres were washed with a mixture of toluene and ethylenediaminetetraacetic acid (EDTA) solution. Pure toluene is not sufficient here because ferric ions may go to the organic 13 ACS Paragon Plus Environment

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phase and form a bond with asphaltenes, as shown by Sung et al.9. Therefore, the EDTA solution is necessary to capture ferric ions from the organic phase since ferric ions have a higher affinity for the EDTA than asphaltenes9. After washing the spheres, the emulsion was centrifuged to separate the organic phase from the EDTA solution. The organic phase, which is composed of dissolved asphaltenes in toluene, was then left on a hotplate under an explosionproof fume hood. The mass of asphaltenes was measured after complete evaporation of toluene. From Table 4, the mass of deposited asphaltenes on the spheres is 20.7% of total infused asphaltenes, which is much lower than the amount of deposited materials including ferric ions. However, compared to the system with no aqueous phase, the amount of deposited asphaltenes in the presence of ferric ions in the bulk phase is slightly lower. Table 4. Amount of deposited materials on the spheres and the PTFE column for the experiment without the presence of an aqueous phase and the experiment with the presence of FeCl3 solution Deposited materials, % of total infused asphaltenes With FeCl3 solution Ferric ions are No aqueous phase Ferric ions are included excluded Spheres 23.4 ± 1.4 36.2 ± 1.4 20.7 ± 1.5 PTFE column 3.6 ± 0.5 12.1 ± 0.1 4.7 ± 0.1 Total 27.0 ± 1.9 48.3 ± 1.5 25.4 ± 1.6 Figure 4 shows the mass of aggregated asphaltenes collected from the effluent for the experiment without an aqueous phase and the experiment with the presence of FeCl3 solution. It can be concluded from Figure 4 that in the presence of ferric ions in the bulk phase, the amount of aggregated asphaltenes increases compared to the system without the ferric ions.


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As reported by Sung et al.9, ferric ions in the bulk phase have a high affinity for asphaltenes and form a complex compound with them. Sung et al.9 also studied other ions, such as Na, Fe (II), Cr (III), and Al (III) ions, and found only ferric ions form a complex compound with asphaltenes. This iron-asphaltene complex may either deposit on the metallic surfaces or aggregate and form larger particles. These large aggregates are moved to the outlet by convection and are then collected from the effluent. More of these large aggregates form in the presence of ferric ions, which act as a flocculant for asphaltenes, and therefore, more asphaltene aggregates are collected from the effluent in the presence of FeCl3 solution compared to the case with no aqueous phase. As a result, less asphaltene was found in the deposited materials in the presence of iron ions. According to several studies available in the literature, it is believed that the larger asphaltene aggregates are less prone to deposit on the surface10,11,26,27. However, due to the presence of iron ions in the deposited materials, the amount of deposition for the experiment with the presence of FeCl3 solution is higher compared to the experiment with no aqueous phase in the system. It should be noted that washing the deposited materials from the carbon steel spheres after the experiment in the presence of FeCl3 solution was not as easy as the washing procedure after the experiment without an aqueous phase. One may conclude that in the presence of ferric ions the deposited materials stick firmly to the metallic tubing and exacerbate the deposition problem.


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No aqueous phase With FeCl3 solution

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Figure 4. Aggregated asphaltenes collected from the effluent vs. the injected P.V. The ASD is 1.01% and 5.21% for “no aqueous phase” and “with FeCl3 solution” experiments, respectively. 3.2. Asphaltene Deposition on Corroded Carbon Steel Spheres To imitate the corroded surface of pipelines or wellbores, carbon steel spheres were corroded prior to being used for the deposition test. The acidic solution used to corrode spheres was prepared by mixing hydrochloric acid with deionized water. The pH and the conductivity values for the acidic solution were the same as the FeCl3 solution used in this study, i.e. 1.32 and 2756 μS/cm. Exposure time to the acidic solution was 6 hours. After the corrosion process, spheres were rinsed first with deionized water and then with acetone. After that, the spheres were dried using nitrogen and were packed into the column. To study asphaltene deposition tendency on a rust-covered metallic surface, the rust was kept on the spheres after the corrosion process. In another experiment, to investigate the effect of the surface roughness on asphaltene deposition, the rust was removed from the corroded spheres using the acidic solution in an ultrasonic bath at 40 kHz for 5 minutes. After the sonication process, the spheres were rinsed 16 ACS Paragon Plus Environment

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first with deionized water and then with acetone and were dried using nitrogen. After the corrosion, the whole process of washing should be very quick to avoid any further corrosion of spheres. Figure 5 shows the surface of the original spheres (before corrosion), the corroded spheres (with rust), and the sphere with a higher surface roughness (after corrosion and without rust). Images were taken using a HIROX KH8700 3D Digital Microscope. (a)

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Figure 5. The surface of the spheres (a) before the corrosion, (b) after the corrosion (with rust), and (c) after the corrosion (without rust) For the deposition tests using the original and corroded spheres, it is assumed that no further corrosion would occur during the experiment since there is no aqueous phase in the system and the spheres are not exposed to air during the deposition test. Thus, the amount of deposited asphaltenes could be quantified directly by comparing the mass of spheres before and after the experiment.


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Table 5 presents the amounts of deposited asphaltenes on the original spheres, on the corroded spheres with rust, and on the corroded spheres without rust. It can be concluded from Table 5 that the amount of deposited asphaltenes quantified on the corroded spheres with and without the presence of the rust is much more than the deposited amount on the original spheres. Table 5. Amount of deposited asphaltenes on the original spheres, on the corroded spheres with rust, and on the corrode spheres without rust.

Spheres

Deposited asphaltenes, % of total infused asphaltenes Corroded spheres Corroded spheres Original spheres (with rust) (without rust) 23.4 ± 1.4 33.3 ± 1.0 33.6 ± 1.5

For the system using the corroded spheres with rust, the presence of iron oxides on the surface seems to facilitate the deposition of asphaltenes. It might be associated with the interaction between iron oxides and asphaltenes. Wang et al.28 reported that in the compositional analysis of deposited materials obtained from an oil field, a significant amount of iron oxide was found. In addition, the amount of asphaltenes adsorbed on iron minerals like hematite is considerably more than on other minerals29. According to the study from Murgich et al.30, low H/C ratio and heteroatom contents of asphaltenes could promote the adsorption on the iron oxide mineral. Furthermore, it was found that the ferric ions on the mineral surface are potential adsorption sites for polar components from the crude oil, such as asphaltenes31. Although the adsorption and deposition of asphaltenes are not equivalent, the presence of iron oxides directly affects asphaltene deposition as shown in this work. The corroded spheres without rust have a higher surface roughness due to the deterioration of iron in the carbon steel spheres compared to the original spheres or the corroded spheres with rust. The higher surface roughness leads to higher surface area for asphaltenes to deposit on.


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According to a study by Hashemi Kiasari et al.26, the surface with higher surface roughness can increase the deposition rate of asphaltenes. Figure 6 depicts the mass of aggregated asphaltenes collected from the effluent for the deposition tests using the original spheres, using the corroded spheres with rust, and using the corroded spheres without rust. For the experiments using the corroded spheres, the amount of aggregated asphaltenes collected from the effluent is much less than the experiment using the original spheres. This indicates that asphaltenes are more prone to deposit on the corroded spheres than the original spheres. 2


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Original spheres Corroded spheres with rust

1.5

Corroded spheres without rust

1

0.5

0 0

2

4 6 8 Injected P.V.

10

12

Figure 6. Aggregated asphaltenes collected from the effluent vs. the injected P.V. The ASD is 1.01%, 0.80%, and 0.89% for the experiments using the original spheres, the corroded spheres with rust, and the corroded spheres without rust, respectively.


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3.3. Mitigation of Iron-Induced Asphaltene Deposition using Ethylenediaminetetraacetic Acid (EDTA) According to the study by Sung et al.9, iron-induced asphaltene precipitation is associated with the bonding between asphaltenes and ferric ions. Also, as previously shown in section 3.1.3., ferric ions available in the bulk phase can lead to significant deposition on metallic surfaces. Therefore, using a chelating agent to sequester ferric ions from asphaltenes seems to be a reasonable strategy for the mitigation of iron-induced asphaltene deposition. In this work, ethylenediaminetetraacetic acid (EDTA) was used as the chelating agent. EDTA is well-known for its excellent chelating performance as well as its low cost9. EDTA is a hexadentate ligand and its fully ionized form can make a very stable complex with a metal ion which results in diminishing the reactivity of the ion. In this study, the EDTA solution was prepared by dissolving the reagent grade disodium salt dihydrate of EDTA in deionized water. The emulsion was prepared by mixing the model oil with FeCl3 and EDTA solutions. The amounts of FeCl3 and EDTA solutions in the final emulsion were 30 vol% and 10 vol%, respectively. Table 6 reports the amounts of deposited asphaltenes on the spheres and the PTFE column for the experiments with the FeCl3 solution and with the FeCl3 and EDTA solutions. The collected deposits on the spheres and the PTFE column were washed by toluene and the EDTA solution using the method previously explained in section 3.1.3 in order to obtain the pure deposited asphaltenes.


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Table 6. Amount of deposited asphaltenes on the spheres and the PTFE column for the experiments with the FeCl3 solution and with the FeCl3 and EDTA solutions

Spheres PTFE column Total

Deposited asphaltenes, % of total infused asphaltenes With FeCl3 and EDTA With FeCl3 solution Solutions 20.7 ± 1.5 7.6 ± 0.5 4.7 ± 0.1 12.8 ± 1.2 25.4 ± 1.6 20.4 ± 1.7

It can be seen from the data presented in Table 6 that the addition of the EDTA solution significantly decreases the amount of asphaltene deposition on the carbon steel spheres (from 20.7% to 7.6% of total infused asphaltenes). EDTA is able to sequester ferric ions from the oil phase and stabilizes these ions by chelation, which results in a decrease of the iron-induced asphaltene deposition. Figure 7 presents the mass of aggregated asphaltenes collected from the effluent for the experiments with the FeCl3 solution and with the FeCl3 and EDTA solutions. It can be seen from Figure 7 that the addition of the EDTA solution to the FeCl3 solution decreases the amount of aggregated asphaltenes collected from the effluent compared to the experiment with the FeCl3 solution only. As shown by Sung et al.9, ferric ions destabilize asphaltenes in the system and more asphaltene precipitation occurs in the presence of these ions. They also found that the EDTA solution can restore the stability of asphaltenes in the system by chelation of iron ions9. Therefore, in this work, both amounts of deposited and aggregated asphaltenes decreased when the EDTA solution was added to the FeCl3 solution since the amount of precipitated asphaltenes decreased compared to the case with the FeCl3 solution only.


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With FeCl3 sloution With FeCl3 solution + EDTA solution 1.5

1

0.5

0 0

2

4

6 8 Injected P.V.

10

12

Figure 7. Aggregated asphaltenes collected from the effluent vs. the injected P.V. The ASD is 5.21% and 2.48% for the experiments with the FeCl3 solution and with the FeCl3 and EDTA solutions, respectively. Although the addition of EDTA decreases asphaltene deposition on carbon steel spheres, the amount of deposited asphaltenes on the PTFE column significantly increases in the presence of EDTA. As reported in the literature, asphaltenes do not tend to deposit on a PTFE surface17,18, and therefore, one may infer that asphaltenes are led by the iron-EDTA complex to go to the PTFE column instead of the metallic spheres. Apparently, the iron-EDTA complex has a high affinity for the PTFE surface and asphaltenes are highly attracted to the ferric ions in the ironEDTA complex. As a result, asphaltenes form a larger deposit on the PTFE column than the carbon steel spheres. Using the PTFE coated tubing for oil production is recently being pursued by the industry in order to reduce the flow assurance problems due to corrosion as well as asphaltene deposition. However, based on the results obtained in this study, if EDTA is used along with a PTFE coating, the PTFE coated surface might suffer from significant organic fouling. 22 ACS Paragon Plus Environment

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Therefore, the combination of different mitigation strategies to control asphaltene deposition requires a careful and systematic analysis.

4. Conclusions In this work, the effect of pipeline corrosion on asphaltene deposition tendency was investigated using a new experimental setup consisting of a multi-section PTFE column packed with carbon steel spheres. It was shown that once ferric ions are available in the oil bulk phase, the amount of deposited materials on metallic surfaces increases considerably. It was also found that iron ions and asphaltenes are highly attracted to each other and form a complex which may firmly stick to a metallic surface. To study the effects of rust-covered metallic surfaces as well as the surface roughness variations on asphaltene deposition, the corroded spheres were used in the packed column. In one case, the iron oxide (rust) was kept on the spheres and significantly higher asphaltene deposition was obtained compared to the experiment with the original spheres. In the other case, the rust was removed from the spheres and it was found that the higher surface roughness considerably increases the amount of deposited asphaltenes. Ethylenediaminetetraacetic acid (EDTA) was used as a chelating agent to sequester iron ions from asphaltenes and mitigate the extent of iron-induced asphaltene deposition. The obtained results showed that the EDTA significantly decreases the amount of deposited asphaltenes on metallic surfaces in the presence of ferric ions. The EDTA solution can increase the stability of asphaltenes in the system by chelation of iron ions. Therefore, both amounts of deposited and aggregated asphaltenes decreased when the EDTA solution was added to the FeCl3 solution since the amount of precipitated asphaltenes decreased in the system compared to the case with the FeCl3 solution only. However, the amount of deposition on the PTFE 23 ACS Paragon Plus Environment

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column increased in the presence of the EDTA. It seems that asphaltenes are led by the ironEDTA complex to go to the PTFE column instead of the metallic spheres. Therefore, the combination of different mitigation strategies, i.e. PTFE coated production tubing and using the EDTA as the chelating agent, should be considered very carefully and the concurrent analysis of the multiple phenomena is strongly recommended.

References 1. Creek, J. L. Freedom of Action in the State of Asphaltenes: Escape from Conventional Wisdom†. Energy Fuels 19, 1212–1224 (2005). 2. Barker, K. M. & Newberry, M. E. Inhibition and Removal of Low-pH-Fluid-Induced Asphaltic Sludge Fouling of Formations in Oil and Gas Wells. in (Society of Petroleum Engineers, 2007). doi:10.2118/102738-MS 3. Moore, E. W., Crowe, C. W., Hendrickson, A. R. & others. Formation, effect and prevention of asphaltene sludges during stimulation treatments. J. Pet. Technol. 17, 1–023 (1965). 4. Houchin, L. R., Dunlap, D. D., Arnold, B. D., Domke, K. M. & others. The occurrence and control of acid-induced asphaltene sludge. in SPE Formation Damage Control Symposium (Society of Petroleum Engineers, 1990). doi:10.2118/19410-MS 5. Ovalles, C. & Rechsteiner, C. E. Analytical Methods in Petroleum Upstream Applications. (CRC Press, Taylor & Francis Group, 2015). 6. Jacobs, I. C. & others. Chemical systems for the control of asphaltene sludge during oilwell acidizing treatments. in SPE International Symposium on Oilfield Chemistry (Society of Petroleum Engineers, 1989). doi:10.2118/18475-MS


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7. Jacobs, I. C. & Thorne, M. A. Asphaltene Precipitation During Acid Stimulation Treatments. in (Society of Petroleum Engineers, 1986). doi:10.2118/14823-MS 8. Fredd, C. N. & Fogler, H. S. Alternative Stimulation Fluids and Their Impact on Carbonate Acidizing. SPE J. 3, 34–41 (1998). 9. Sung, C.-A., Tavakkoli, M., Chen, A. & Vargas, F. M. Prevention and Control of Corrosion-Induced Asphaltene Deposition. in (Society of Petroleum Engineers, 2016). doi:10.4043/27008-MS 10. Eskin, D., Ratulowski, J., Akbarzadeh, K. & Pan, S. Modelling asphaltene deposition in turbulent pipeline flows. Can. J. Chem. Eng. 89, 421–441 (2011). 11. Tavakkoli, M. et al. Asphaltene Deposition in Different Depositing Environments: Part 1. Model Oil. Energy Fuels 28, 1617–1628 (2014). 12. Wang, J., Buckley, J. S. & Creek, J. L. Asphaltene Deposition on Metallic Surfaces. J. Dispers. Sci. Technol. 25, 287–298 (2004). 13. Vargas, F. M. & Tavakkoli, M. Asphaltene Deposition: Fundamentals, Prediction, Prevention, and Remediation. (CRC Press, 2018). 14. Tavakkoli, M. et al. Effect of Emulsified Water on Asphaltene Instability in Crude Oils. Energy Fuels 30, 3676–3686 (2016). 15. Vilas Bôas Fávero, C., Hanpan, A., Phichphimok, P., Binabdullah, K. & Fogler, H. S. Mechanistic Investigation of Asphaltene Deposition. Energy Fuels 30, 8915–8921 (2016). 16. Melendez, A. A. Experimental study of the effect of commercial dispersants on the precipitation, aggregation and deposition of asphaltenes. (Rice University, 2015). 17. Gonzalez, D. L. Modeling of asphaltene precipitation and deposition tendency using the PC-SAFT equation of state. (Rice University, 2008).


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18. Tavakkoli, M., Panuganti, S. R., Taghikhani, V., Pishvaie, M. R. & Chapman, W. G. Asphaltene Deposition in Different Depositing Environments: Part 2. Real Oil. Energy Fuels 28, 3594–3603 (2014). 19. Kuang, J. et al. Assessment of the performance of asphaltene inhibitors using a multisection packed bed column. Fuel (2018). doi:10.1016/j.fuel.2018.11.059 20. Kuang, J. et al. Investigation of Asphaltene Deposition at High Temperature and under Dynamic Conditions. Energy Fuels (2018). doi:10.1021/acs.energyfuels.8b03318 21. Vargas, F. M., Creek, J. L. & Chapman, W. G. On the Development of an Asphaltene Deposition Simulator. Energy Fuels 24, 2294–2299 (2010). 22. Aslan, S. & Firoozabadi, A. Effect of Water on Deposition, Aggregate Size, and Viscosity of Asphaltenes. Langmuir 30, 3658–3664 (2014). 23. Mittal, K. L. Contact Angle, Wettability and Adhesion. 6, (CRC Press, Taylor & Francis Group, 2006). 24. Starkweather, B. A., Zhang, X. (Shaw) & Counce, R. M. An Experimental Study of the Change in the Contact Angle of an Oil on a Solid Surface. Ind. Eng. Chem. Res. 39, 362– 366 (2000). 25. Wang, J., Fan, T., Buckley, J. S. & Creek, J. L. Impact of Water Cut on Asphaltene Deposition Tendency. in (Offshore Technology Conference, 2014). doi:10.4043/25411-MS 26. Hashemi Kiasari, H., Rabbani, A. R., Mousavi Dehghani, S. A. & Qobadi, A. Modeling Asphaltene Deposition Rate on to Inner Surface of Oil Production Wells (Stainless Steel) Using Novel Quartz Crystal Nanobalance Experiments. J Dispers Sci Technol (2014). doi:10.1080/01932691.2014.880845


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Effect of Carbon Steel Corrosion on Asphaltene Deposition - Energy

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