Effect of a Cationic Surfactant as a Chemical Destabilization of Crude

Article pubs.acs.org/jced

Effect of a Cationic Surfactant as a Chemical Destabilization of Crude Oil Based Emulsions and Asphaltene Stabilized Azadeh Mirvakili,† Mohammad Reza Rahimpour,*,†,‡ and Abdolhossein Jahanmiri†,‡ †

Department of Chemical Engineering, School of Chemical and Petroleum Engineering, Shiraz University, Shiraz 7193616511, Iran Gas Center of Excellence, Shiraz University, Shiraz 7193616511, Iran

‡

ABSTRACT: This work relates generally to the use of surfactants in oil field acidizing operations to reduce emulsion and sludge formation in such operations. The demulsifier and antisludge are two of the most important additives in oil well acidizing. During oil well acidizing, an antisludge agent prevents asphaltene aggregation (sludge formation), and a demulsifier agent breaks the oil film in acid emulsion. Most of the antisludge agents presented before were anionic surfactants, whereas demulsifier agents were cationic surfactants. But in this study we have introduced a cationic surfactant as an antisludge and a demulsifier agent simultaneously. This cationic surfactant is a quaternary ammonium compound, didecyl dimethyl ammonium chloride (QAM), compared with dodecyl benzene sulfonic acid (DDBSA), which is introduced as a strong antisludge in literature, and NE32, which is a commercial antisludge agent. Then, QAM is compared with NE13, which is a commercial demulsifier. The experiments are conducted based on API RP 42 standard test for both agents. The results show that the QAM is a multiobjective additive which has antisludge and demulsifier properties simultaneously. However, the QAM is shown to be more effective than DDBSA and NE32 as an antisludge agent but less effective than NE13 as a demulsifier.

1. INTRODUCTION One of the main functions of acid stimulation is to remove formation damage to enhance the productivity of the oil producing zones. Two major problems encountered during the stimulation of oil-producing wells are the precipitation of asphaltene particles and the formation of acid-in-oil emulsions, which include sludge formation. These viscous emulsions and sludges can plug formation and cause further well damage. They also cause operational problems in the surface facilities following acid stimulation.1 1.1. Asphaltene Particles. Asphaltenes are defined as the hydrocarbon fractions soluble in toluene and insoluble in n-heptane, which are heavy polycyclic aromatic compounds forming nanocolloidal particles dispersed and/or suspended in oil. These nanocolloidal aggregates are the heaviest components in crude oil with by far the lowest effective diffusion coefficients in the oil.1 Mullins has demonstrated that asphaltenes are dispersed and/or suspended in crude oils and/or solvents in three forms: molecules, nanoaggregates, and clusters of nanoaggregates. He emphasized the different asphaltene hierarchical structures and will show how the hierarchical structures are related in terms of structure and energies.2 Asphalthene aggregation occurs during acidizing operations, and sludge is formed in the reservoir. The sludge formation mechanism is not clear; however, some sludge formation mechanisms are presented previously, but these mechanisms are not acceptable today. Asphalthene aggregation occurs in the oil reservoir naturally. Thus, in the oil well acidizing, antisludge should have the required ability for sludge particle size control. Indeed, antisludge agents should prevent cluster formation so that the formed sludges are smaller than the reservoir pores and they cannot © 2012 American Chemical Society

block the reservoir pores in the acidizing oil wells. Jacobs presented primary factors promoting sludge, including using hydrochloric (HCl) acid during acidizing operations. Increasing HCl acid strength will result in increasing sludge. In fact, 28 % HCl should never be used in the presence of asphaltenic crudes. Ironcontaminated acid, especially the ferric (Fe III) ion, accelerates sludging. The use of liquids with a low surface tension such as diesel can also cause sludge.3,4 Every effort should be made to avoid asphaltene aggregation or sludge formation. Loony and McDougall introduced an antisludge agent, an ester of sulfonic acid such as monoethoxylated dodecyl benzene sulfonic acid,5 which is useful for acid-stimulated hydrocarbon-containing formations. Dyer invented anionic compositions containing an alkyl aryl sulfonic acid or salt thereof, a nonethoxylated glycol, and an acetylenic alcohol in an alkyl alcohol solvent. These compositions have proved effective for controlling sludge and emulsion formation during acid stimulation and treatment of hydrocarbon wells.6 Campbell presented compositions which involve the demulsification and liquification of hydrocarbon-based sludges. The object of the invention is to provide a hydrocarbon-based sludge that is sufficiently liquefied to be pumped and demulsified enough to allow the waters, oils, and solids in the sludge to separate.7 Knopp provided a composition for either inhibiting or preventing the formation of emulsions in the presence of treating acids during the acid stimulation of hydrocarbon wells. The composition includes an alkyl aryl Received: December 14, 2011 Accepted: April 14, 2012 Published: May 17, 2012 1689

dx.doi.org/10.1021/je2013268 | J. Chem. Eng. Data 2012, 57, 1689−1699

Journal of Chemical & Engineering Data

Article

oil−water interface, rupture or weaken the rigid film, and enhance water droplet coalescence. There are thousands of products that have been patented as crude oil demulsifiers. Royle selected a demulsifier, from the group consisting of a long chain carboxylic acid ester of a polyhydric alcohol, and added it to the acidizing solution comprised of hydrochloric and hydrofluoric acids which are injected through a well into a subterranean petroleum formation.13 Spalding methods and compositions are presented, which are effective for preventing or resolving emulsions of oil in aqueous solutions, preferably for preventing or resolving oil in water emulsions formed in aqueous brines used as completion fluids or workover fluids.14 Zaki et al. studied the stability and rheology of an Egyptian heavy crude oil-in-water emulsions stabilized by an anionic (TOS) and nonionic (NPE) surfactants individually or in a mixture. The study reveals that the viscosity of the crude oil decreases when it is emulsified with water in the form of an oilin-water type of emulsion. The stability of the oil-in-water emulsion increases as the surfactant concentration and speed of mixing of the emulsion increases.15 Mokadam presented an ester or salts of sulfonated fatty acids, which exhibits both antisludge and demulsification properties.16 Campbell disclosed a demulsifier and liquefaction agent which contains a salt of DDBSA, poly(propylene glycol), and citrine.17 1.3. Objective. This work relates generally to the use of surfactants in oil field acidizing operations to reduce emulsion and sludge formation in such operations. A cationic surfactant is introduced as a novel multiobjective additive for the acidizing process. This substance is a quaternary ammonium belonging to cationic surfactants category. QAM as an antisludge has been compared with an antisludge commercial additive named NE32 from BJ Services Co. and DDBSA which is presented as an antisludge in literature. Then, it was compared with a commercial demulsifier (NE13 from BJ Services Co.) as a demulsifier. All of the materials are tested in the presence of the heavy crude oil, first, and then the selected materials, which are proper in the heavy crude oil, are tested in the presence of the medium and soft crude oil. The experiments were conducted based on standard test of API RP42.18

sulfonic acid or salt thereof, an acetylenic alcohol, and an alkyl diphenyl oxide sulfonic acid or derivative thereof in an alkyl alcohol solvent.8 Fogler and Chang investigated the stabilization of crude oil asphaltenes in apolar alkane solvents using a series of alkylbenzene-derived amphiphiles as the asphaltene stabilizers. They present a study on the influence of the chemical structure of these amphiphiles on the effectiveness of asphaltene solubilization and on the strength of asphaltene− amphiphile interaction using both UV−vis and Fourier transform infrared (FTIR) spectroscopies. The results showed that the amphiphile's effectiveness of asphaltene stabilization was primarily controlled by the polarity of the amphiphile's headgroup and the length of the amphiphile's alkyl tail. Increasing the acidity of the amphiphile's headgroup could promote the amphiphile's ability to stabilize asphaltenes by increasing the acid−base attraction between asphaltenes and amphiphiles.9 1.2. Oil-in-Acid Emulsions. One of the most significant problems created by the acidization treatment is the subsequent formation of very stable oil-in-water emulsions in the produced fluids from the well. Studies have indicated that the most stable emulsions are formed from spent acid and material simulating formation fines.10 Emulsion stability is maintained by a combination of physical and chemical mechanisms. The breaking of an emulsion is also called demulsification, since the aim is to separate the original mixture into its parts.11 Demulsification is the breaking of a crude oil emulsion into separate phases of oil and water. From a thermodynamic point of view, an emulsion is an unstable system because there is a natural tendency for a liquid/liquid system to separate and reduce its interfacial area and, hence, its interfacial energy. This stability arises from the formation of interfacial films that encapsulate the oil droplets. To separate this emulsion into oil and water, the interfacial film must be destroyed and the droplets made to coalesce. Therefore, destabilizing or breaking emulsions is directly linked to the removal of this interfacial film. The factors that affect the interfacial film and, consequently, the stability of the emulsions are temperature, agitation, residence time, and solids. The application of heat promotes oil/water separation and accelerates the treating process. An increase in the temperature causes reducing viscosity of the oil and increasing the mobility and settling rate of water. Also, the temperature increase causes more droplet collisions and favors coalescence. Increasing the temperature also makes a greater in densities of fluids, which leads to the enhancement of water-settling time and separation. Solids have a strong tendency to stabilize emulsions, especially if they are presented as fines or when they are wetted by both oil and water. Removing the solids or their source is sometimes all that is required for eliminating or reducing the emulsion problem.12 The most common method of emulsion treatment is the addition of demulsifiers. Demulsifiers are surface-active compounds that, when added to the emulsion, migrate to the

2. EXPERIMENTAL SECTION 2.1. Materials and Equipment. There are wide ranges of surfactants that can be used in oil well acidizing for antisludge and demulsifier agents. The surfactants used in this study are shown in Table 1. Some solvents are used in these experiments that are shown in Table 2. In addition we used hydrochloridric acid, 37 %, from Dr. Mojallali Chemical Laboratories Co.; crude oils, which are used for these sets of experiments, are obtained from three oil fields: Bangestan soft crude oil, Gachsaran medium crude oil, and Cheshmeh-khosh heavy crude oil. Their physical characteristics are shown in Table 3. The crude oil chemical composition is shown in Table 4. We used two commercial agents. One of them is NE32 (antisludge), which is obtained from BJ Services Co.; another one is NE13

Table 1. Surfactants Used as an Antisludge Agent no.

common name

IUPAC name

chemical formula

purity

supplier

1 2 3 4 5 6

dodecyl benzene sulfonic acid benzene sulfonic acid toluene sulfonic acid phenol sulfonic acid ammonium acetate didecyl dimethyl ammonium chloride

4-dodecylbenzenesulfonic acid benzenesulfonic acid hydrate 4-methylbenzenesulfonic acid hydrate 4-hydroxybenzenesulfonic acid acetic acid ammoniate didecyl-dimethylammonium chloride

C12H25C6H4SO3H C6H8O4S CH3C6H4SO3H.H2O C6H6O4S C2H7NO2 C22H48ClN

0.98 > 0.99 > 0.99 > 0.99 > 0.99 > 0.99

Behdash Co. Merck Co. Merck Co. Merck Co. Merck Co. Merck Co.

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Table 2. Solvents Used for the Composition of Antisludge Agents no.

name

IUPAC Name

chemical formula

1 2 3 4 5 6

methanol xylene toluene isopropanol ethylene glycol propylene glycol

methanol dimethylbenzene methylbenzene propan-2-ol ethane-1,2-diol propane-1,2-diol

CH4O C8H10 C7H8 C3H8O C2H6O2 C3H8O2

mass density (kg·m−3) at 15 °C viscosity (mPa·s) at 15 °C salt content of produced water (kg·m−3) mass fraction of wax mass fraction of water mass fraction of saturates mass fraction of aromatics mass fraction of resins mass fraction of asphalthenes

medium oil

soft oil

1006 29.95 17 0.064 0.1838 0.322 0.464 0.135 0.068

868 21.7 205 0.078 0.0442 0.45 0.32 0.08 0.05

687 18.3 85 0.083 0.0867 0.56 0.28 0.046 0.034

supplier

0.995 0.99 0.99 0.99 0.99 0.99

Dr. Mojallali Chemical Laboratories Co. Arman Sina Co. Dr. Mojallali Chemical Laboratories Co. Arman Sina Co. Dr. Mojallali Chemical Laboratories Co. Merck Co.

immediately into a 100 cm3 graduated cylinder and the volume of water breakout at elapsed time intervals reported. Tests are conducted at ambient laboratory temperature.18 The performance of the demulsifier is measured in terms of percent volume of acid separated AS (mass fraction), which is defined as: m As = acid separation (mass fraction) = 0 m

Table 3. Characterization of Crude Oils heavy oil

purity > > > > > >

where m is the mass of the acid separation and m0 is the original mass of oil contained.

3. RESULTS 3.1. Sludge Test Result. DDBSA is one of the most widely used antisludges; some of its common derivatives such as benzene sulfonic acid (BSA), toluene sulfonic acid (TSA), and phenol sulfonic acid (PSA) (anionic surfactants) are compared with ammonium acetate (AMA) and quaternary ammonium (cationic surfactant) in the presence of the heavy crude oil (Cheshme-Khosh Oil Field). The results are shown in Table 5.

(demulsifier), which was also obtained from BJ Services Co. Bottles with screw caps were used, and a 100-mesh stainless steel screen was used. Gas oil (from Iranian Oil Refinery Co.) and pentane (from Merck Co.) were used as solvents of paraffin and resin. Pulverized formation fines were used from Dallan carbonate reservoir rock. The water bath used for the experiments was of Memmoret. 2.2. Acid Sludge Test. This experiment has been conducted based on an American Petroleum Institute (API) RP 42 standard test. Pouring 50 cm3 acid solution, which contains a specific amount of antisludge agent, into a clean bottle is followed by adding an equal volume of crude oil, free of solids and emulsion. Then the bottle is covered and shaken vigorously. Next, the mixture is placed in a water bath at formation temperature and stands quiescent for 24 h. Then the mixture is carefully poured through a clean, 100-mesh stainless steel wire screen. If no solids remain on the screen, no sludge has been formed. If solids are present, the screen should be washed alternately with warm water and gas oil and pentane. This will remove emulsions and paraffins but will not remove sludge caused by acid. The amount of sludge according to the list below is described: No sludge: no solid particles retained on the screen. Trace: a very few small particles on the screen. Moderate: particles obviously present. Heavy: many large particles. This procedure should be repeated using the acid sludge preventive agent at the concentration specified by the supplier.18 2.3. Emulsion Test for Carbonate Acidizing. Experiments using acid with specific concentrations are repeated. This is followed by dispersing 2.5 g of pulverized formation fines to acid. Next, 50 cm3 of crude oil is added to the 50 cm3 acid dispersion and then the solution is emulsified with the mixer at (14 000 to 18 000) rpm for 30 s. The emulsion must be poured

Table 5. Comparison of Different Surfactants as an Antisludge Agent in Heavy Oil abbreviation

precipitated sludge/g

dodecyl benzene sulfonic acid benzene sulfonic acid

DDBSA

0.006

no sludge

BSA

0.983

toluene sulfonic acid

TSA

1.12

phenol sulfonic acid ammonium acetate

PSA AMA

0.127 1.36

didecyl dimethyl ammonium chloride without additive

QAM

0.004

moderate sludge moderate sludge trace sludge moderate sludge no sludge

name of material

result

3.42

In this step, all surfactants are used 0.01 mass fraction in acid solution (1 g surfactant/100 g acid), and the acid concentration is 15 %. As it can be seen in Table 5, the mass of the precipitated sludge was used as a criterion to gauge the functionality of the used antisludge. In fact the precipitated sludge is precipitated asphaltene which was not able to pass through the 100 mesh sieve. In this regard to prevent asphaltene precipitation, one could suggest using a surfactant to stick on

Table 4. Chemical Composition of Crude Oils component

C1

C2

C3

IC4

NC4

IC5

NC5

C6

C7 +

H2S

CO2

N2

mole fraction in heavy oil mole fraction in medium oil mole fraction in soft oil

0.3718 0.0021 0.0008

0.0990 0.0042 0.0016

0.0610 0.027 0.008

0.0126 0.0109 0.0053

0.0338 0.0380 0.0386

0.0119 0.0224 0.0230

0.0128 0.0303 0.0462

0.0461 0.0548 0.0663

0.3430 0.8095 0.8100

0.000 0.000 0.000

0.0053 0.0008 0.0002

0.0027 0.000 0.000

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Table 6. Effect of Different Solvents on the Performance of Antisludge Agents in Heavy Oil solvent

methanol

xylene

precipitated sludge/g result

0.76 heavy sludge

0.12 moderate sludge


3.06 heavy sludge

2.59 heavy sludge





3.21 heavy sludge

2.92 heavy sludge


3.32 heavy sludge

3.17 heavy sludge


0.012 no sludge

0.007 no sludge

toluene

isopropanol

50 % DDBSA and 50 % Solvent 0.11 0.72 moderate sludge moderate sludge 50 % BSA and 50 % Solvent 2.63 2.71 heavy sludge heavy sludge 50 % PSA and 50 % Solvent 1.49 1.52 moderate sludge moderate sludge 50 % TSA and 50 % Solvent 3.07 3.16 heavy sludge heavy sludge 50 % AMA and 50 % Solvent 3.21 3.29 heavy sludge heavy sludge 50 % QAM and 50 % Solvent 0.0075 0.011 no sludge no sludge

the asphaltene surface and form micelles to decrease the chance of asphaltene and acid contact. As could be concluded from Table 5, DDBSA and QAM are good candidates to use as applicable surfactants. They retain asphaltene precipitation because they contain long length chains which are to able form stable steric layers around asphaltene. Other surfactants (PSA, TSA, and BSA) are not efficient because all of them are short length chain surfactants. The surfactants which are able to stabilize the asphaltene can either be anionic or cationic. In Table 6 the effect of the different solvents on the functionality of the surfactants is discussed in the presence of the heavy crude oil and 15 % acid concentration. As it can be seen in Table 6, different solvents, namely, toluene and xylene, were used which can dissolve asphaltene. It is worth mentioning that these solvents were previously used as antisludge agents. In this direction an antisludge agent with a mass fraction of 0.01 was used. This fraction contained 50 % solvent and 50 % surfactant (0.5 g of surfactant + 0.5 g of solvent in 100 g of solution). Comparing Tables 5 and 6 revealed that a decrease on the surfactant concentration leads to the reduction of antisludge effectiveness. While there is no observed sharp trend about the effect of solvents, ethylene glycol and propylene glycol showed the best functionality based on the above findings. In the rest of the experiments, due to the negligible effect of solvent addition, the surfactant was used alone. In this section the effects of DDBSA and QAM under different conditions and acid concentrations in the presence of the heavy crude oil were investigated, and the obtained results were compared with the commercial surfactant, namely, NE32, which is obtained from BJ Services Co. The results for the case of 15 % acid concentration are given in Table 7. As it is obvious from the table, for DDBSA and NE32 the amounts of the precipitated asphaltene are approximately the same. In addition for both concentrations of 0.007 and 0.01 mass fraction, there was no observed asphaltene precipitation for DDBSA and NE32. Another presented surfactant is QAM. QAM is more effective in comparison with DDBSA and NE32. It can be used as 0.001 mass fraction in heavy oil well acidizing with a 15 % acid concentration.

ethylene glycol

propylene glycol

0.10 trace sludge

0.095 trace sludge

2.13 heavy sludge

1.93 heavy sludge



2.71 heavy sludge

2.47 heavy sludge

3.01 heavy sludge

2.87 heavy sludge

0.006 no sludge

0.004 no sludge

Table 7. Comparison of QAM with DDBSA and NE32 in 15 % Acid Concentration and in Heavy Oil HCl 15 % heavy crude oil usage additive mass fraction additive name precipitated sludge/g result

0.01

0.007

0.005

0.003

0.006

0.016

DDBSA 0.12 0.58

no sludge

no sludge

additive name precipitated sludge/g result

0.004

0.0058

no sludge

no sludge


0.007 no sludge

0.001

0.87

trace sludge QAM 0.0073

trace sludge

trace sludge

0.0098

0.016

no sludge

no sludge

0.093

no sludge NE32 0.138

0. 67

0.94

no sludge

trace sludge

trace sludge

trace sludge

The effects of the DDBSA, QAM, and NE32 in the 20 % acid solution on the asphaltene aggregation and precipitation in the presence of the heavy crude oil were also investigated. The obtained results (see Table 8) show that for QAM the optimum concentration (mass fraction) is 0.001, because at this concentration no sludge was formed, while the optimum concentration of NE32 and DDBSA is 0.007. Generally the given results in Table 8 demonstrate that, when the acidic content of the solution increases, more surfactant is required. Finally the effects of the DDBSA, QAM, and NE32 on the asphaltene precipitation and aggregation in the 28 % acid solution in the presence of the heavy crude oil were investigated. The obtained results that are shown in Table 9 illustrate that QAM is a more effective additive in comparison with the other two additives (DDBSA, NE32) in 28 % acid concentration. This observed trend might be related to the stronger interaction of QAM on the asphaltene surface that leads to higher ability to prevent asphaltene aggregation. The obtained results for different additives including DDBSA, NE32, and QAM at different acid concentrations are 1692



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Table 8. Comparison of QAM with DDBSA and NE32 in 20 % Acid Concentration and in Heavy Oil HCl 20 % heavy crude oil usage additive mass fraction additive name precipitated sludge/g result

0.01

0.007

0.005

0.003

0.009

0.068

DDBSA 0.158 0. 76

no sludge

no sludge


0.007

0.0097

no sludge

no sludge


0.010 no sludge

0.001

1.03

trace trace sludge sludge QAM 0.038 0.091

moderate sludge

trace sludge

0.081

no no sludge sludge NE32 0.182 0.88

no sludge

trace sludge

moderate sludge

trace sludge

0.28

1.14

Table 9. Comparison of QAM with DDBSA and NE32 in 28 % Acid Concentration and in Heavy Oil HCl 28 % heavy crude oil usage additive mass fraction additive name precipitated sludge/g result additive name precipitated sludge/g result additive name precipitated sludge/g result

0.01

0.007

0.005

0.003

0.0108

0.086

DDBSA 0.398 0.898

no sludge

trace sludge

0.009

0.012

no sludge

no sludge

0.014 no sludge

0.001

1.17

trace trace sludge sludge QAM 0.062 0.13

moderate sludge

trace sludge

0.097

no trace sludge sludge NE32 0.536 1.07

trace sludge

trace sludge

moderate sludge

moderate sludge

0.45

1.34

shown in Figure 1a−c. Figure 1a shows that for DDBSA an increase in the acid concentration leads to more precipitation of asphaltene. The overall conclusion from Figure 1a is that for acid concentrations lower than 20 % the optimum concentration of DDBSA should be higher than 0.005 mass fraction, while for the acid concentrations higher than 20 % the optimum mass fraction of the DDBSA should be higher than 0.007. In Figure 1b the effect of the commercial additive of NE32 on the asphaltene precipitation is observed. For NE32, the trend was similar to DDBSA (Figure 1a). In other words the additive lower limit concentration for acid lower than 20 % should be 0.005 mass fraction, while for acid concentrations higher than 20 % the additive lower limit concentration should be 0.007 mass fraction. In addition it can be inferred from Figure 1c that the effect of QAM on reduction of the asphaltene precipitation is more than two previously investigated additives (DDBSA and NE32). The obtained results show that for different acid concentrations of 15 %, 20 %, and 28 % a lower amount of QAM concentration is needed. In the acidizing process where a significant well corrosion and stone solubilization in acid occur, the production of iron ions including Fe2+ (ferrous) and Fe3+ (ferric) is

Figure 1. Effect of different antisludge agents: (a) DDBSA, (b) NE32, and (c) QAM on preventing asphalthene precipitation in various acid concentrations and in the presence of heavy crude oil: ●, HCl 15 %; +, HCl 20 %; □, HCl 28 %.

possible. In literature it is presented that Fe 3+ leads to extreme sludge formation. Therefore, the utilization of an iron-reducing agent is necessary. The iron-reducing agent reduces from a ferric ion (Fe3+) to a ferrous ion (Fe2+). Thus the utilization of iron-reducing agent leads to decreasing positive charges in the acidizing medium. Sludge formation decreases as a result of positive charge reduction in the medium. Reducing agents are applicable to decrease the stabilization of asphaltene, due to decreasing positive charges in the medium. In this direction experiments in the presence of iron controller agents and acid containing ferrous (0.0075 mass fraction) and ferric (0.0025 mass fraction) ions in the presence of the heavy crude oil were conducted. The obtained results for the effect of ferric and ferrous presence in the different acid 1693



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Table 10. Comparisons of Different Compositions of Different Antisludge and Different Iron Control Agents in (a) 15 % Acid Concentration, (b) 20 % Acid Concentration, and (c) 28 % Acid Concentration and in Heavy Oil (a) HCl 15 %, 0.0075 mass fraction Fe2+, 0.0025 mass fraction Fe3+ Heavy Crude Oil

a

additive

Ferrotrol 200

Ferrotrol 300

QAM

NE32

precipitated sludge

test no.

mass fraction

mass fraction

mass fraction

mass fraction

g

resulta

1 2 3 4 5 6 7 8 9 10 11 12 13 (without additive) 14 15

0.01

3.1 2.87 0.92 0.66 1.59 1.21 0.008 0.006 0.83 0.62 0.102 0.008 3.42 0.0086 0.167

H* H T* T M* M N* N T T T N H N T

0.01 0.01

0.005 0.005

0.01 0.01

0.005 0.005

0.01 0.01

0.008 0.008

0.01 0.01

0.008 0.008 0.01 0.01

0.01 0.01 0.01 0.01

0.01 (b) HCl 20 %, 0.0075 mass fraction Fe2+, 0.0025 mass fraction Fe3+ Heavy Crude Oil

additive

Ferrotrol 200

Ferrotrol 300

QAM

NE32

test no.

mass fraction

mass fraction

mass fraction

mass fraction


0.01 0.01 0.01

0.005 0.005

0.01 0.01

0.005 0.005

0.01 0.01

0.008 0.008

0.01 0.01

0.008 0.008 0.01 0.01

0.01 0.01 0.01 0.01

0.01 (c) HCl 28 %, 0.0075 mass fraction Fe2+, 0.0025 mass fraction Fe3+ Heavy Crude Oil

additive

Ferrotrol 200

Ferrotrol 300

QAM

NE32

test no.

mass fraction

mass fraction

mass fraction

mass fraction


0.01 0.01 0.01

0.005 0.005

0.01 0.01

0.005 0.005

0.01 0.01

0.008 0.008

0.01 0.01

0.008 0.008 0.01 0.01

0.01 0.01 0.01 0.01

0.01

precipitated sludge g

result

3.26 2.98 1.08 0.98 1.76 1.53 0.024 0.011 0.96 0.81 0.123 0.0094 3.42 0.034 0.185

H H M T M M N N T T T N H N T

precipitated sludge g

result

3.40 3.21 1.74 1.56 2.06 1.97 0.036 0.027 1.12 1.08 0.235 0.012 3.42 0.054 0.212

H H M M M M N N M M T N H N T

*H: high sludge; *T: trace sludge; *M: moderate sludge; *N: no sludge.

concentrations are given in Table 10. In this step, two commercial iron controller agents (Ferrotrol 300 and Ferrotrol 200)

and two antisludge agents (NE32, QAM) were used for preventing asphaltene precipitation. In the first series of 1694



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Table 11. Comparison of QAM with NE13 in the Medium Oil and in (a) 15 % Acid Concentration and (b) 28 % Acid Concentration (a) HCl 15 % medium crude oil usage additive mass fraction additive name precipitated sludge/g result

0.01

0.007

0.005

DDBSA 0.088 no sludge additive name QAM precipitated sludge/g 0.002 0.0026 0.0058 result no no no sludge sludge sludge additive name NE32 precipitated sludge/g 0.005 0.0098 0.0912 result no no no sludge sludge sludge (b) HCl 28 % medium crude oil 0.004 no sludge

usage additive mass 0.01 fraction additive name precipitated sludge/g 0.0076 result no sludge additive name precipitated sludge/g 0.005 result no sludge additive name precipitated sludge/g 0.0075 result no sludge

0.0092 no sludge

0.007

0.0103 no sludge 0.0093 no sludge 0.011 no sludge

0.005 DDBSA 0.1098 trace sludge QAM 0.0212 no sludge NE32 0.2341 trace sludge

0.003

0.001

0.28 trace sludge

0.55 trace sludge

0.0078 no sludge

0.0103 no sludge

0. 21 trace sludge

0.68 trace sludge

0.003

0.001

0.564 trace sludge

0.87 trace sludge

0.093 no sludge

0.185 trace sludge

0.684 trace sludge

0.934 trace sludge

Table 12. Comparison of QAM with NE13 in the Soft Oil and in (a) 15 % Acid Concentration and (b) 28 % Acid Concentration (a) HCl 15 % soft crude oil usage additive mass fraction 0.01 0.007 0.005 additive name DDBSA precipitated sludge/g 0.0024 0.0056 0.0087 result no no no sludge sludge sludge additive name QAM precipitated sludge/g 0.0018 0.0023 0.0042 result no no no sludge sludge sludge additive name NE32 precipitated sludge/g 0.0026 0.0063 0.0092 result no no no sludge sludge sludge (b) HCl 28 % soft crude oil

Figure 2. Precipitated asphalthene mass fractions in the presence of DDBSA, QAM, and NE32 with different quantities and acid concentrations: (a) 15 %, (b) 20 %, and (c) 28 % acid concentrations in heavy oil.

experiments the acid concentration was maintained fixed at 15 %, and an iron control agent with 0.01 mass fraction was added. Then different concentrations of QAM and NE32 were added to the solution. As shown in rows 1 and 2 of Table 10a, the addition of antisludge is necessary since the addition of iron control agents solely is not significantly effective to prevent asphaltene precipitation. Therefore, iron controller additives were added to the two solutions. The first solution consisted of 15 % acid and 0.005 mass fraction of QAM, and the second one consisted of 15 % acid and 0.005 mass fraction of NE32. Comparing these two experiments revealed that the addition of 0.005 mass fraction of QAM leads to the precipitation of trace sludge, while the addition of 0.005 mass fraction of NE32 leads to the precipitation of moderate sludge. In other words the results demonstrated that QAM is more efficient than NE32 to

usage additive mass fraction additive name precipitated sludge/g result additive name precipitated sludge/g result additive name precipitated sludge/g result

1695

0.01

0.007

0.005

DDBSA 0.0038 0.0076 0.0103 no no no sludge sludge sludge QAM 0.0027 0.0045 0.0083 no no no sludge sludge sludge NE32 0.0039 0.0079 0.0123 no no no sludge sludge sludge

0.003

0.001

0.018 0.0485 no no sludge sludge 0.0086 0.0102 no no sludge sludge 0.022 0.0531 no no sludge sludge 0.003

0.001

0.0273 0.0781 no no sludge sludge 0.0102 0.0463 no no sludge sludge 0.0312 0.0589 no no sludge sludge



Article

Figure 4. Comparisons of (a) QAM and (b) NE13 as a demulsifier in 20 % acid concentration and with the heavy oil: *, 0.01; ○, 0.007; ●, 0.005; ×, 0.003; +, 0.001 mass fraction.


a formation of higher than 0.80 mass fraction sludge, while the addition of 0.005 mass fraction of both QAM and NE32 decrease the asphaltene precipitation to 0.2 and 0.4 mass fractions, respectively; finally the addition of 0.008 mass fraction of QAM and 0.01 mass fraction of NE32 leads to no precipitation of asphaltene. Results of Figure 2b,c are similar to Figure 2a. The above results show that QAM is effective antisludge additive for heavy oil well acidizing. In this step, QAM, DDBSA, and NE32 are compared in the presence of medium and soft crude oils. The precipitated sludges are presented in Table 11 in various acid concentrations with medium crude oil. As seen in Table 11a,b, QAM is also more effective than other agents in the presence of medium crude oil. The optimum concentration of QAM is 0.001 and 0.003 mass fractions in medium oil well acidizing with acid concentrations of 15 % and 28 %, respectively. In Table 12, the antisludge strengths of QAM, DDBSA, and NE32 are compared in the presence of soft oil and various acid concentrations. All of them are proper for soft oil well acidizing, but QAM is also better than others. The results of experiments show that QAM is a strong antisludge that it is effective even in low concentrations in the presence of the heavy, medium, and soft crude oil. QAM is a cationic surfactant which is adsorbed well on asphaltene. QAM has long chains that form a steric layer on asphaltene. Thus QAM can resist acid attack to asphaltene, and it is able to prevent sludge formation.

decrease the asphaltene precipitation. In the next step the concentrations of QAM and NE32 are increased to 0.008 and 0.01 mass fractions in the presence of 0.01 mass fraction of iron controller agent. These experiments show that the optimum concentrations for QAM and NE32 to prevent asphaltene precipitation were 0.008 and 0.01 mass fractions, respectively. The previous experiments were performed at the acid concentration of 20 % in the presence of the heavy crude oil. The obtained results in Table 10b show that at higher acid concentrations more asphaltene precipitation was observed for both QAM and NE32. In addition it can be found that in the presence of Ferrotrol 300 the optimum concentration of QAM and NE32 were 0.008 and 0.01 mass fractions, respectively, to observe no asphaltene precipitation. In Table 10c the results of NE32 and QAM addition to 28 % acid solution in the presence of iron controller agents and with the heavy crude oil are presented. The previous results are obtained from Table 10c. The precipitated asphalthene mass fractions in the presence of different surfactants with different quantities are presented in Figure 2. Comparisons were done in different acid concentrations. Results are shown in Figure 2a−c for acid concentrations 15 %, 20 %, and 28 %, respectively, in the presence of the heavy crude oil. The precipitated asphaltene mass fraction is presented in all of the experiment stages (test no.). Stages of experiments are introduced in Table 10. As it can be observed in Figure 2a, using no antisludge leads to 1696



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Figure 6. Comparison of QAM and NE13 in medium oil (a) in 15 % acid concentration and (b) in 28 % acid concentration: ●, 0.01 NE13; △, 0.007 NE13; +, 0.01 QAM; ○, 0.007 QAM; ×, 0.005 NE13; □, 0.005 QAM.


3.2. Demulsifier Test Results. Another advantage of QAM is demulsifying oil in the acid. Therefore it can be used as a demulsifier in acidizing processes. We used QAM as the demulsifier agent and compared QAM with a commercial demulsifier agent (NE13). Experiments were conducted based on an API RP 42 standard test at room temperature. However, rising temperature which is one of the reservoir conditions enhances the demulsification of oil in the acid emulsion because rising temperature leads to increasing molecule momentum and the emulsion breaks easier. Results of demulsifier experiments in 15 % acid concentration in the presence of the heavy crude oil are presented in Figure 3. Acid separation percentage in the presence of QAM as a demulsifier in 15 % acid concentration is shown in Figure 3a. It is illustrated in Figure 3a that the acid separation percentage increases with increasing QAM concentration. Maximum acid separation occurs in the first 2 min in the presence of QAM. Since acid separation should occur fast, higher concentrations of QAM are acceptable. Figure 3b shows the acid separation percentage versus time in the presence of NE13 as a demulsifier. The acid separation percentage increases with increasing NE13 concentration. Maximum separation occurs in the first 2 min for mass fractions higher than 0.005 of NE13. The comparison between Figures 3a,b shows that the demulsification strength of NE13 is less than QAM. But a higher concentration of QAM can be used as a demulsifier because the acid separation percentage in the presence of QAM is almost close to

NE13 at higher concentrations. Therefore QAM is a multiobjective additive with two properties (antisludge and demulsifier). Results of demulsifier experiments in 20 % and 28 % acid concentrations in the presence of the heavy crude oil are presented in Figures 4 and 5, respectively. Results are similar to Figure 3, but an increase in acid concentration leads to a decrease in acid separation. Thus, in higher acid concentrations a higher concentration of demulsifier must be used. QAM and NE13 as a demulsifier agent are tested in different oils and acid concentrations. These results are presented in Figures 6 and 7. These agents are tested in the presence of medium oil in 15 % and 28 % acid concentrations, and results are shown in Figure 6a and b, respectively. QAM is a proper demulsifier agent, but it is weaker than NE13 (commercial agent). When the acid concentration increases, the oil-in-acid emulsion breaks in more time. QAM and NE13 are tested in soft oil, and results are presented in Figure 7. Figure 7a shows the performance of QAM and NE13 as a demulsifier agent in 15 % acid concentration. Results show that the oil-in-acid emulsion breaks easily in this condition in the presence of both agents. Also Figure 7b shows the ability of QAM and NE13 for breaking oil-in-acid emulsion in 28 % acid concentration. From a comparison between Figure 7a and b, it can be concluded that increasing acid concentration leads to extend the time of emulsion breaking. 1697



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high concentrations. Therefore, QAM is a powerful surfactant that prevents the sludge formation and breaks the oil film in acid emulsion. QAM is a good additive from an economical viewpoint because it is cheap (about 4 dollars/liter) and it can be used less than commercial agents, but it is hazardous.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +98 711 2303071; fax: +98 711 6473180. E-mail address: [email protected] (M.R. Rahimpour). Currently on sabbatical at the University of California, Davis, CA; e-mail: [email protected]. Funding

The authors would like to recognize the support of the South Zagross Gas and Oil Company. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Zuo, J. Y.; Mullins, O. C.; Freed, D.; Zhang, D.; Dong, C.; Zeng, H. Analysis of Downhole Asphaltene Gradients in Oil Reservoirs with a New Bimodal Asphaltene Distribution Function. J. Chem. Eng. Data 2011, 56, 1047−1058. (2) Mullins, O. C. The Modified Yen Model. Energy Fuels 2010, 24, 2179−2207. (3) Jacobs, I. C.; Thorne, M. A. Asphaltene Precipitation during acid stimulation treatments, in Proceedings of the international symposium of formation damage of SPE; Society of Petroleum Engineers: Richardson, TX, 1986; Paper SPE 14823. (4) Jacobs, I. C. Chemical Systems for the Control of Asphaltene Sludge During Oilwell Acidizing Treatments, Presented at the SPE International Symposium on Oilfield Chemistry in Houston, TX, Feb 8−10, 1989; SPE 1845. (5) Loony, J. R.; Mcdougall, L. A. Use of esters of sulfonic acid as anti-sludge agents during the acidizing of formations containing sludging crude oils. U.S. Patent 4442014, 1984. (6) Dyer, R. J. Anionic compositions for sludge prevention and control during acid stimulation of hydrocarbon wells. U.S. Patent 5622921, 1997. (7) Campbell, G. Sluge liquefaction process and agents. U.S. Patent 6440330 B1m 2002. (8) Knopp, M. S. Non-emulsifying anti-sludge composition for use in the acid treatment of hydrocarbon well. U.S. Patent 7507695 B2, 2009. (9) Chang, C. L.; Fogler, H. S. Stabilization of asphaltenes in aliphatic solvents using chemical structure of amphiphiles on asphaltene stabilization alkylbenzene-derived amphiphiles. 1. Effect of the chemical structure of amphiphiles on asphaltene stabilization. Langmuir 1994, 10, 1749−1757. (10) Royle, R. A. Demulsifier for inclusion in injected acidization systems for petroleum formation stimulation. U.S. Patent 4290901, 1981. (11) Ramesh, M.; Sivakumar, A. Hydrophobically-modified demulsifiers for oil-in-water systems. U.S. Patent 5635112, 1997. (12) Menon, V. B.; Wasan, D. T. Particle-Fluid Interactions With Applications to Solid-Stabilized Emulsions Part III. Asphaltene Adsorption in the Presence of Quinaldine and 1,2-Dimethylindole. Colloids Surf. 1987, 23, 353. (13) Royle, R. A. Demulsifier for inclusion in injected acidization systems for petroleum formation stimulation. U.S. Patent 1981, 4290901. (14) Spalding, W. A. Demulsifier for aqueous completion fluids, U.S. Patent 6914036 B2, 2005. (15) Ahmed, N. S.; Nassar, A. M.; Zaki, N. N.; Gharieb, H. K. H. Stability and rheology of heavy crude oil-in-water emulsion stabilized

Figure 7. Comparison of QAM and NE13 in soft oil (a) in 15 % acid concentration and (b) in 28 % acid concentration: *, 0.01 NE13; △, 0.007 NE13; ×, 0.01 QAM; □, 0.007 QAM; ○, 0.005 NE13; +, 0.005 QAM.

4. CONCLUSION To enhance the performance of acidizing process some additives should be added to the acid. If acid enters solely into the oil well, sludge will be formed, which leads to permeability reduction of rgw reservoir. In addition, owing to stone solubility in acid, there are fines that are dissolved in both oil and acid. These particles cause increasing stability of oil-inacid emulsion since fines are dissolved in both of fluids and aggregates around of the emulsion. Therefore adding an antisludge agent and demulsifier to acid in the acidizing process is strongly essential. Substances used as antisludge and demulsifier additives are surfactants. In this study a cationic surfactant is introduced which is a novel antisludge and demulsifier agent simultaneously. As antisludge agent it has been compared with DDBSA and NE32 via API RP42 standard test. DDBSA is introduced as an antisludge in literature, and NE32 is a commercial antisludge agent. The experiment results show that QAM is a strong antisludge that prevents sludge formation better than the others. QAM has a high effect on preventing sludge formation even in low concentrations. Therefore the use of QAM as an antisludge is economical. Even, when the test is performed in the presence of iron ions, which are one of the coagulating factors, QAM prevents the asphaltene coagulation (sludge formation). Although QAM is a more reliable antisludge than DDBSA and NE32 in term of a demulsider is weaker than commercial demulsifier agent (NE13). The demulsification power of QAM is about 5 % less than NE13. QAM can be an effective demulsifier in 1698



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by an anionic nonionic surfactant mixture. Pet. Sci. Technol. 1999, 17, 553−576. (16) Mokadam, A. R. Surfactant additive for oil field acidizing. U.S. Patent 5797456, 1998. (17) Campbell, G. J. Sludge demulsification process and agents. U.S. Patent 5858247, 1999. (18) Laboratory testing of surface active agents for well stimulation, 2nd ed.; American Petroleum Institute: Washington, DC, 1977; API RP 42.

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