Insight into the Chemistry of Surfactant-Based Enhanced Oil Recovery Processes

Recent Patents on Chemical Engineering, 2009, 2, 1-10

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Insight into the Chemistry of Surfactant-Based Enhanced Oil Recovery Processes Benyamin Yadali Jamaloei* Chemical & Petroleum Engineering Department, Schulich School of Engineering, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada  Received: Octob er 14, 2008; Accepted: Nove mber 12, 2008; Revised: No vember 24, 2008 

Abstract: During the past several decades, significant and considerable research has been carried out on secondary and tertiary recovery of trapped residual oil remaining within the producing formations underground despite the efficient, current primary production strategies and methods. Methods have been sought of increasing oil recovery, while revamping and improving the economic viability and efficiency of operations. One method that has received much attention and intensive study over these past decades is the use of surfactant-based chemical flooding. Initial patents and laboratory tests have shown conclusively that chemical solutions and slugs including surfactants, remove considerable oil from the porous medium normally trapped after initial waterflooding. Oil recovery processes by means of surfactant micellar solutions or microemulsions have included the injection of slugs of varied compositions. Patents on surfactant-based enhanced oil recovery processes (such as dilute surfactant flooding, surfactant/polymer flooding, and alkaline/surfactant/polymer flooding) have been issued, starting from the 1920’s and particularly after the 1960’s, when the technology was put on a scientific basis. These patents were generally concerned with the chemistry of surfactant-based enhanced oil recovery processes including envisioning the use of chemical solutions (slugs) to decrease the surface tension between oil and the flooding medium, screening of surfactants for oil recovery efficiency, chemical (surfactant) slug designs and formulation to mobilize residual oil, documenting petroleum sulfonates useful in surfactant flooding, and other important factors in the chemistry of surfactant-based chemical flooding processes. Moreover, evaluation and determination of optimum chemical systems (slugs) for the best economics for a specific field application have been disclosed and documented in several large oil companies’ patents in the surfactant-polymer area. In this article, a full-fledged review of the patents on different aspects of the chemistry of surfactant-based enhanced oil recovery processes is presented.

Keywords: Surfactant, enhanced oil recovery, chemistry, chemical slug, patent. INTRODUCTION Technically, chemical flooding is regarded as a general term for injection processes that inject chemical solutions (slugs or systems) into the reservoir. Surfactant-based substances, and/or alkali are used in solution to reduce surface tension between oil and water in the reservoir, whereas polymers are deployed to improve displacement sweep efficiency. Micellar-polymer and alkaline flooding are regarded as the two major chemical flooding processes. Micellar flooding (also known as microemulsion flooding or surfactant flooding) is a process in which a surfactant slug is injected into the formation followed by a larger slug of water containing polymer (normally a high-molecular-weight  polymer) which improves mobility and sweep efficien cy. Different forms of surfactant-based chemical flooding have  been reported in the literature (alkali/surfactan (alkal i/surfactan t/polymer t/polym er (ASP) flooding, surfactant/polymer (SP) flooding, surfactant flooding, dilute surfactant flooding, etc.). The injection scheme for a surfactant-based chemical flooding includes injecting first a preflush, a chemical solution, a mobility *Address correspondence to this author at the Chemical & Petroleum Engineering Department, Schulich School of Engineering, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada; Tel: +1 403 543 7917; E-mail: [email protected]

1874-4788/0 9 $100.00+.00

 buffer and, finally, a driving fluid, which displaces the chemicals and the developed oil bank towards producer. In general, surfactant slugs are composed of a hydrocarbon phase, surfactant, cosurfactant and an aqueous  phase. The literature literatur e contains numerous numero us ternary diagram diagra m representations for these components. These phase diagrams reveal the various phases that may form and develop in the reservoir as residual oil is mobilized and displaced towards  production  produ ction well. In the literature, surfactant surfact ant slug has also  been referred to as micellar solution s, microemu lsions, soluble oils, swollen micelles, etc. The primary purpose of a surfactant slug is to lower interfacial tension and displace the trapped residual oil normally after reservoir has been flooded  by water. The technical and patent literature literatur e contains a number of surfactant slug designs and formulations and variety of techniques that are used to screen surfactant slugs for use as potential oil recovery agents. Adsorption of surfactants surfactants within surfactant slug on minerals is an important aspect of any surfactant-based chemical flooding. It is regarded as a major cause of surfactant retention and slug  breakdow n. This has been one o ne of o f the active research areas in chemical enhanced oil recovery. Regarding the above general discussion on surfactant slug, one would expect a seriously complex chemistry for the design and implementation of the chemical slug in all © 2009 Bentham Science Publishers Ltd.

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surfactant-based enhanced oil recovery processes. This  becomes even severe when consider ing that chemistry of  petroleum sulfonates sulfon ates is extremely complex. compl ex. Since a petropetro leum feedstock contains variety of chemical structures. Moreover, individual components of a chemical slug vary in composition, with many patented micellar formulas. Hence, evaluations to determine which chemical slug offers the best economics for a specific field application are often complex since an infinite array of chemical variables must be considered for this evaluation task. Petroleum sulfonates and useful chemical slugs in surfactant flooding have been disclosed in several patents. However, virtually there is not enough detailed information in the non-patent technical literature. In the subsequent sections, a brief overview of some important patents on the chemistry of surfactant-based chemical flooding is presented. These patents have focused on the proper formulation of chemical slugs and appropriate design of surfactant-based chemical flooding processes. EARLY PATENTS

In the patent history of surfactant-based chemical enhanced oil recovery (EOR), for the first time, in 1927, a  patent was issued to Atkinson . In that patent, he propose d that surface tension between crude oil and reservoir rock can  be reduced using so ap or other aqueous solutions [ 1]. The technical and patent literature bears several surfactant slug design methods and formulations in the area of surfactant-based enhanced oil recovery processes. Most of these patents described different formulations of chemical solutions including surfactant, cosurfactant, hydrocarbonwater and or salt concentrations which result in specific slug design and property [2-9]. In 1959, Holm and Bernard [10]  proposed that surfac tant adsorptio n in water-w et porou s medium can be reduced by injecting 0.1-0.3% concentration of surfactant dissolved in a hydrocarbon solvent with a low viscosity. In l961, Csaszar [11] documented the use of a mixture of an anhydrous soluble oil and a nonaqueous solvent containing up to 12% surfactant. In 1962, Gogarty and Olson [12] cited the use of microemulsions in a new miscible-type recovery process known as Maraflood. The Gogarty and Olson patent suggested the injection of a small fraction of the pore volume of micellar solution containing a surfactant concentration greater than about 5%. Patents have been issued to Jones [13, 14], in 1967, claiming the use of highwater-content, oil-external microemulsions and waterexternal micellar dispersions in oil recovery. In a relatively different ground, Harvey [15] patented a process using dead  bacterial and/or yeast cells to carry nonionic surfactan ts [poly(ethylene oxide) ethers or thioethers] as EOR slugs through the reservoir. Using such slugs in laboratory sand column reservoir models, he obtained 20-30% recovery of residual oil. PATENT SURVEY 1970-1989

 Novel cost-efficient cost-eff icient design of chemical slugs for EOR  purposes has been always of particular p articular concern over the p ast decades. What was disclosed in the early patents was continuously followed to be covered in the next several

Benyamin Yadali Jamaloei

decades with the basic difference that some other modern methods for chemical slug design started to emerge. Roszelle [16] discussed a process in which a water-external micellar dispersions contacts with air or nitrogen to form (in-situ or on the surface) a stable foam. This micellar dispersion contained hydrocarbon, surfactant, and water (50-95% by volume). In the same year, new combinations of surfactants and bacteria were suggested for use in EOR drive fluids. Wagner and Stratton [17] and Hitzman [18] suggested that the commercial surfactant-treated dead bacterial cells can be deployed in EOR drive fluids by eliminating the requirement for injecting live bacterial cells into a reservoir for effective channeling of the injection water. Also, some novel EOR chemical processes and methods were started to emerge in the number of patents in the chemical EOR area in 1970’s. A process for the recovery of oil from an oil reservoir was proposed by Burdyn et al. [19]. Surfactants are formed within the reservoir by injection of a n aqueous alkaline solution (and optionally followed by a second alkaline slug containing a thickening agent) and neutralizing the organic acids in the reservoir oil. The injected solution contained sufficient alkaline agent to create a pH within the range of 11.5-13 and a monovalent salt within the range of 0.5–2.0 weight p ercent. Screening of petroleum sulfonates- which are generally known as the most available and commercial types of surfactants- and manipulation of their combination in a chemical slug has been always of particular interest to the researchers. Plummer et al. [20] invented an aqueous  petroleum sulfonate sulfonat e mixture which contained, at least, two different petroleum sulfonates. The implemented sulfonates had an average equivalent weight within the range of about 390–450. The hydrocarbon portion of the sulfonate had an average aliphatic to aromatic proton ratio within the range of about 4–20 moles per mole. Use of some hydrocarbon solvents together with some colloidal materials in a given chemical slug has been also  presented in some patents . Specifically, Specific ally, in 1976, a method metho d was invented by Christopher et al. [21] for recovering oil from reservoirs which contained both oil and an aqueous  phase. According Accord ing to the proposed propo sed method, fluid included a slug of a mixture of hydrocarbon solvent, colloidal silica, water and a high molecular weight polymer. This slug of chemical mixtures then is followed by another fluid which can drive the chemical solution (slug) within the porous medium. They also invented a novel displacing fluid design for the above-cited process. Use of sacrificial systems in chemical EOR, was disclosed in some patents. In one of these important patents, recovery of oil from a reservoir by use of an alkaline agentsulfonate surfactant system in conjunction with the injection of a sacrificial system- which contains an inorganic  polyphosphate  polyph osphate and an alkali metal carbonate- was proposed propo sed  by Chang’s patent [22] in 1976. An aqueous initiation slug and an alkaline are injected into the reservoir. Aqueous initiation slug contained an inorganic polyphosphate, and alkali selected from the group consisting of alkali metal and ammonium hydroxides. In this invention, the pre-flush slug is followed by the injection of surfactant slug which contains an alkaline agent and a sulfonate surfactant. After injection

Chemical Aspects of Surfactant-based EOR

of the surfactant slug, an aqueous driving fluid is injected in order to displace the oil toward a production system [22]. Some patents have focused on use of chemical slugs to specifically alter the wettability of formations in order to enhance the oil recovery. As a particular instance, in 1977,  Needham et al. [23] filed for a patent specifying a newly designed process according to which the quantity of oil recoverable from an already waterflooded predominantly oilwet formation could be increased. This can be achieved by  passing a first solution through the formation format ion to change the formation from its oil-wet to a water-wet state. The first solution then is followed by passing a second solution which has high interfacial tension with the oil throughout the formation. This will force the oil from the sm all pores of the formation into larger ones. Finally, a third solution is passed which has low interfacial tension with the oil in the reservoir. They also cited that passing a mobility buffersolution through the reservoir to prevent viscous fingering and consequent channeling, and finally passing the driving fluid through the formation completes this new chemical EOR process design [23]. Recovery of oil from oil reservoirs by waterflooding employing an alkaline agent and a sulfonate surfactant had  been commonly in research market marke t for several decades. decades . Burdyn et al. [24] filed for a patent in which a similar but modified version of such process has been expounded. They described that an aqueous initiation slug (preflush) is injected into the reservoir which contains an alkaline agent and ammonium hydroxides. This preflush slug is then followed by an aqueous surfactant slug (containing a sulfonate surfactant and an alkaline agent). Subsequent to injection of the surfactant slug, oil is displaced by an aqueous flooding medium whose portion may contain a thickening agent for mobility control [24]. Some patents have accentuated some biochemistry aspects of a certain chemical EOR process. As an instance, for the first time, in 1980, a waterflood process was described in detail by Chang [25]. In this process, a slug of  biopolymer is injected into a formation forma tion before injection of the synthetic polymer slug to prevent the synthetic polymer from degradation when it contacts formation brine or surfactants surfactants present in the reservoir. Patents have been issued which are particularly on synthesis of novel chemicals useful in a certain chemical EOR process. A novel methodology for isolation of native  petroleum surfac tants for lowering interfacial interfaci al tensions in aqueous-alkaline systems was explained by Yen et al. [26]. They explained the petroleum synthesis with the capability of surface tension reduction at high pH values. Surfactant fraction of the petroleum can be extracted by petroleum distillation in the temperature range of 100–200ºC. This fraction is concentrated by removing its benzene-soluble components. The resulted fraction can be injected as a slug into the oil reservoir to enhance alkaline/water flooding  process. It is also possible to mix the obtained fraction with  petroleum, or enrich it with the residue , or alternativ ely the residue can be mixed with petroleum. Each of these combinations can be injected as slug to help alkali/water flooding process. Yen et al. mentioned that:” amenability of a reservoir for alkaline flooding can be determined by

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separating the native surfactant fraction and measuring its interfacial tension with water at the proposed alkalinity of the floodwater.” [26]. In 1980, a novel aqueous surfactantcontaining fluid appropriate for use in general surfactant based oil recovery recover y flooding process es, and an oil recover y  process using the above-cited above- cited fluid was disclosed by Carlin et al. [27]. This fluid contained petroleum sulfonates alone or in combination with solubilizing cosurfactants such as ethoxylated alkyl or alkylaryl compounds, alkyl or alkylaryl  polyethox y sulfates, or alkyl or alkylaryl polyetho xy sulfonates. The aforementioned synthetic petroleum sulfonate was a mixture of petroleum sulfonates of varying equivalent weights ranging from 250 to 700, with an average equivalent weight between 325 and 425 [27]. In some previously published patents, researchers tried to  present novel processes and chemical slug designs suitable for specific circumstances of formation temperature, salinity, etc. This has become a major concern over these decades. Shupe et al. [28] documented an oil recovery process suitable for use in formations with temperature from 70 to 300ºF, and water salinity of 70,000 to 220,000 parts per million total dissolved solids. In this process, a viscous emulsion, microemulsion or micellar dispersion fluid is injected into the reservoir to recover the oil. The author clearly stated that [28]:” proposed emulsion contained at least two surfactants such as an alkylpolyalkoxyalkylene sulfonate or alkylarylpolyalkoxyalkylene sulfonate and also a nonionic surfactant which is individually insoluble in the cosolvent (alkanol, or ethoxxylated alkylphenol).” Regarding salinity issues, a water-external phase viscous emulsion was designed by Cardenas et al. [29]. This emulsion contained a water soluble and/or dispersible alkylpolyalkoxyalkylene sulfonate or alkylarylpolyalkoxyalkylene sulfonate and a water-dispersible and/or soluble petroleum sulfonate as a  phase-stabilizing  phase-s tabilizing additive. They explained in detail that this is an effective fluid for flooding formations containing brine whose salinity is from 70,000 to 220,000 parts per million total dissolved solids and also having temperatures up to 300ºF. They also showed that designed emulsion is phasestable over a wide range of formation temperatures and water salinities and hardness values [29]. Synthesis of new chemicals useful in chemical EOR  processe s from industrial chemical chemic al effluents has been documented in some published patents. Especially, in 1982, Johnson et al. [30] filed for a patent in which the synthesis of a sacrificial or competitive adsorbate for surfactants contained in chemical flooding emulsions was disclosed. Adsorption of surfactant on the rock surfaces is reduced by injection of this adsorbate prior to or concurrent with the chemical emulsion. This reduction is allotted to the adsorption of this adsorbate on the mineral surfaces within the formation. In a different mode, surfactant can be displaced from the mineral surface by injection of the adsorbate immediately after chemical flood. This adsorbate was a caustic effluent from the bleach stage or the weak black liquor from the digesters and pulp washers of the Kraft  pulping p rocess [30 ]. Also, proper combination of alcohols and other chemicals to synthesize new cosurfactants (cosolvent) for surfactant-based EOR processes was one of the major

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concerns in the chemistry of such processes. Alford et al. [31] provided an improvement in emulsifier systems for use in the tertiary recovery of oil comprising a surfactant and an alcohol cosurfactant which was a mixture of alcohols having no more than 12 carbon atoms. Economic viability and feasibility of any surfactant based chemical chemica l EOR process, has been the foremos t  parameter in the design of chemical slugs. Synthesis of chemicals (surfactant, cosurfactant, hydrocarbon phase and aqueous phase) used in a certain chemical slug from wellsite chemicals-such as wellhead chemicals- to reduce the operating costs of the process has been a challenging issue. Regarding this, Watson and Butler [32] explained a novel chemical slug design which included several steps. Sour wellhead gas is collected from the well whose hydrogen sulfide is oxidized to sulfur trioxide. The resulted sulfur trioxide will be reacted with a well-site hydrocarbon mixture. Sulfonated petroleum mixture is produced from this reaction after which a neutralizing agent is added to this sulfonated petroleum mixture. This makes a surface active  petroleum sulfonate salt mixture mixtur e that can be used within the surfactant slug as the main component [32]. Lipowski et al. [33] filed for a patent in which the  preparation of an amphoter ic water-in-oil water-in -oil self-inver ting  polymer emulsion was documented docu mented which contained a copolymer or a terpolymer in the aqueous phase, a hydrocarbon oil for the oil phase, a water-in-oil emulsifying agent, and an inverting surfactant. This water-in-oil emulsion was  prepared according accordin g to the m ethod mention ed by the authors: au thors: “dissolving the required monomers in the water phase, dissolving the emulsifying agent in the oil phase, emulsifying the water phase in the oil phase to prepare a water-inoil emulsion, homogenizing the water-in-oil emulsion,  polymerizing the monom ers dissolved dissolv ed in the water phase of the water-in-oil emulsion to obtain the copolymer or tertpolymer and then adding the self-inverting surfactant to obtain an amphoteric water-in-oil self-inverting water-in-oil emulsion”. They proposed that this multipurpose emulsion can be very useful in surfactant-based chemical flooding  processes if included includ ed within the chemical slug [33]. One of the most severe limitations of surfactant-based chemical flooding is the instability and retention of the employed surfactants (or tensides) in the ionic environments of oil reservoirs. Such limitations have been considered and investigated in several patents. Balzer [34] explained the  process for the tenside flooding of reservoirs r eservoirs of m edium and high salinities, which included injecting an emulsion of an oil phase, an aqueous phase, and carboxymethylated oxethylate, by flooding before and/or after a solution or dispersion of carboxymethylated oxethylate. In each case, the tenside and/or the emulsifier was selected so that the  phase inversion temperature temperatu re of the system of reservoir reservo ir oil/flooding water/tenside/optional additives or reservoir oil/flooding oil/flooding water/emulsifier/optional water/emulsifier/optional additives, respectively, lies about 0 to 10ºC above the reservoir temperature. This method dramatically reduced tenside retention as compared with the published literature results to that date [34]. In some patents surfactants and other chemicals were screened for potential use in desired chemical processes. Dilgren [35] filed for a patent relating to improving a process

Benyamin Yadali Jamaloei

for displacing oil by injecting steam and a foam-forming surfactant into the reservoir. He expounded in detail an improved procedure for determining which surfactant material is most effective for a particular reservoir. Designing efficient chemical slugs capable of tolerating fluctuating temperature conditions-commonly encountered in oil reservoirs-has been investigated in some patents. In one of these patents, recovering crude oil by injecting a liquid solution consisting essentially of at least one surfactant such as alkyl toluene sulfonate in an aqueous medium and injecting a gas to displace the movable oil effectively toward a production well was proposed by Chang and Kralik [36] in 1988. This process was found to be advantageous in formations where temperatures preclude effective oil recovery using micellar/polymer chemical floods [36]. Methods for in situ production of surface-active materials are one of the potential ways that can reduce the operating costs of a chemical flood process. Gregory [37] proposed one of the potential ways of in-situ formation of surfaceactive material in alkaline flooding wherein alkali present in the flooding material reacts with petroleum acids in the oil to  produce  produ ce surface-active surface-a ctive agents at the oil-water oil-w ater interfac e. He designed a cosurfactant-enhanced alkaline flooding in w hich a preformed surfactant is added to the flooding material. According to the explained details in this patent, the primary surfactant is formed by reaction in the formation and the added preformed surfactant is addressed as cosurfactant. He also explained that in some oil reservoirs, it is impossible to maintain a high pH in the flooding material since these reservoirs contain large quantities of calcium sulfate (anhydrite which is a slightly soluble salt) as a constant source of calcium ions which may react with the alkali, in the cosurfactant-enhanced cosurfactant-enhanced alkaline f looding material [37]. Employing surfactants in some thermal EOR and solvent based operations operat ions has been disclosed in some patent publipubli cations. Borchardt [38] explained an improved process for recovering oil by injecting a mixture of steam and steam foam surfactant into an oil formation in both steam drive and steam soak operations. He mentioned that [38] “this improvement was provided by using a rapidly foaming steam foam surfactant, either alone or in combination with a second steam foam surfactant (any steam foam surfactant which forms a strong foam, such as alpha olefin sulfonate, alkyltoluene sulfonate, alkyxylene sulfonate, or alpha olefin sulfonate dimer) added to an aqueous solution of electrolyte, and optionally also a noncondensible gas in a multi-state surfactant injection process.” In addition, in 1989, Falls [39]  proposed  propo sed an invention for improvem ent in an oil recover y  process: “CO2, aqueous solution and an anionic surfactant are injected into a reservoir to displace oil, with the injection  pressure and rate of fluid production arranged so that the CO2  is pressurized to at least more than the reservoir fluid  pressure. ” This Thi s improvemen impr ovemen t reduce s the extent to which wh ich the th e surfactant is absorbed on the reservoir rocks. Falls also cited that [39]: “this was performed by including an amount of monovalent cationic salt of carbonic acid within the aqueous  phase of the injected fluid which is effective for increasin g the pH of the solution, at the conditions encountered within the reservoir, to an extent which reduces the level of adsorption of the surfactant.”

Chemical Aspects of Surfactant-based EOR

In Table 1, summary of some important (in terms of  presenting more novelties) patents from 1970 to 1989 has  been given g iven in wh ich the th e emphasis emp hasis is on the rendered ren dered novelty in each work. PATENT SURVEY 1990-2008

In 1990’s and the first decade of the present century, research has continued on the major areas as had been continuously performed in previous decades. Introducing new methods to synthesize new chemicals had been of m ajor concern in the mentioned two decades. Loza [40] presented an invention regarding novel C-branched zwitterionic surfactants and introduced an enhanced oil recovery method using the foregoing surfactants. Maddox [41] introduced a method for modifying a sulfonate surfactant flooding system so as to permit the use of fluids of increased salinity in the  polymer drive. 0.05-1.0 weight percent percen t of a divalent metal cation is added to alter the sulfonate mixture. Then, 0.1-1.5%  by weight of a sulfonate sulfona te solubiliz er is added to the polymer polyme r drive fluid [41]. Surfactants were designed by Loza et al. [42] which were tolerant to the presence of divalent ions. These novel surfactants required required that sulfonation must be on the aromatic ring and that the alcohol component had to have an alkyl  branched side group. It was discover ed by the Loza et al. that the surfactants of this invention are able to tolerate divalent ion presence in the order of greater than 20,000  ppm. This can be compared to the conventio nal commercial commerc ial sulfonates such as dodecylbenzene sulfonate which can only tolerate up to 100 ppm concentration of divalent ion [42]. Over these nearly two decades, processes have been  proposed to meet me et certain cer tain reservoir r eservoir or operating o perating conditions or to make avail of a specially designed chemical slug. Balzer [43] proposed a new process which provided gentle surfactant effectiveness even at extreme temporary and/or local temperature fluctuations. A mixture of a carboxymethylated oxethylate and a polyglucosyl sorbitol fatty acid ester was used to establish this. Recovery of oil by such surfactant flooding was useful in reservoirs with temporary or local temperature changes. Pinschmidt et al. [44]  proposed  propos ed the use of injection fluid for chemical chemica l EOR  purposes possessin g a viscosifyin g amount amoun t of a poly (vinylamine). This fluid undergoes in-situ high-temperature hydrolysis in strongly acidic or alkaline formation. The authors claimed that this process is applicable to enhanced oil recovery fluids for water-flooding, well completion or workover, and acidifying or fracturing purposes. Lau et al. [45] invented a gas foam flooding process using a mixture of surfactant solution (an olefin sulfonate surfactant enriched in olefin disulfonate) and gas. This surfactant mixture decreases the interfacial tension, produces strong foam capable of fast  propagation throughout through out the porous medium, medium , and can dramatically reduce residual oil saturation to lower level as compared to the conventional surfactants. These properties can be achieved if the carbon number is selected properly [45]. in situ  Application of high temperature resistant surfactants to produce water continuous emulsions for improved crude recovery was incorporated by Gregoli, et al. [46]. As discussed by the authors, this process included injecting into the wellbore an emulsifying composition which contains an aqueous phase and a minor amount of an

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emulsifying agent such that the emulsifying composition contacts at least a portion of the hydrocarbon to form an oilin-aqueous phase emulsion within the reservoir. A process was explained by Schramm [47] for enhancing the recovery of oil which involved injecting a surfactant-containing foam having oil-imbibing and transporting properties. A foam having such properties was selected either by determination of the lamella number or by micro-visualization techniques. The effectiveness of enhanced oil recovery methods has been addressed by introducing a safe form of carbon disulfide comprising one or more salts of tri- and tetrathiocarbonic acid. This was explained in detail in Kissel’s patent [48]. Bloodworth et al. [49] reported surfactants with gentle emulsifier action and long-term high stability in the pH range from 5 to 10 and breakdown out of this range. This would make these surfactants as appropriate emulsifiers for enhanced oil recovery purposes [49]. Prukop [50] described a method of recovering heavy oil included injecting an aqueous surfactant solution comprising about 0.1-5% by weight of an alkoxylated nonionic or ionic surfactant containing a viscous oil phase. This was achieved  by using an alkoxylated alko xylated surfactan t having sufficient suffici ent ethylene eth ylene oxide groups, propylene oxide groups, or both to have a cloud point above about 100ºF and below reservoir temperature [50]. Current [51] discovered a surfactant composition useful for coacting with emulsions in a reservoirs which included at least two surfactant components, one anionic and the other a non-ionic surfactant. The ratio of components was selected to reduce the viscosity of the emulsion in a petroleum reservoir to near that or less than that of the oil phase alone. Advantages were obtained by using such composition which includes a combination of surfactant components for viscosity reduction in a petroleum reservoir leading to synergistic combination of surface active components [51]. A process for improved heavy oil recovery was introduced by Di Lullo [52]. This was achieved by means of an aqueous dispersion of the petroleum product. In the aqueous slug, a dispersant should be alkali metal or ammonium salts of organic sulfonates. These sulfonated must  possess sulfur content of at least 10% 10 % and water solubility solubil ity of of at least 15% by weight in the temperature of 20ºC [52]. Prukop [53] discussed a method for recovering surfactants from the produced fluids. This was achieved by mixing 0.1–5% of a nonionic surfactant and produced fluids (this nonionic surfactant must have a phase inversion temperature above the temperature of the produced fluids). The resulting mixture is heated above the phase inversion temperature and mixed with water. Finally, mixture is cooled to reach a temperature below the phase inversion tem perature after which the surfactants surfact ants can be easily extracted extracte d [53]. A stable monophasic liquid composition was explained in detail by Keys [54] which possesses the ability to stabilize increased amounts of surfactant while retaining the mono phasic state. In his patent, patent , Key clearly stated that [54]:” another aspect of this invention is the method of increasing the amount of cationic, anionic, amphoteric, or nonionic surfactant or a mixture of two or more of them that can be

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Table 1.

Benyamin Yadali Jamaloei

Summary of Some Important Patents from 1980 to to 1989 in Surfactant-ba sed Chemical EOR

Inventor(s)

EOR Method

Surfactant

Cosurfactant

Roszelle (1970)

Surfactantenhanced foam flooding

 Nonionic, cationic, and anionic, sodium and ammonium petroleum sulfonates

Primary  butanols,  primary  pentanols and secondary

Alkali or Other Additives

Polymer

Method a Approach and/or Novelty

-

-

Injecting a foam of a water-external micellar dispersion and displacing the foam with a drive fluid 

-

PA or PS

Corrosion inhibitors, and bactericides, can

hexanols Plummer & Roszelle (1975)

Surfactant flooding

Sulfonate blends

Alcohols,  preferably 3 to 8 carbon atoms

Christopher & Satter (1976)

Hydrocarbon solvent flooding

High molecular weight alkyl sulfates or sulfonates or nonionic surfactants

-

 be added Colloidal silica used as thickener for the solvent portion

PA

Reducing permeability of the reservoir to water

Optional

Wettability change and

of the slug Chang (1976)

Alkaline-

Inorganic polyphosphate

-

sulfonate water flooding  Needham et al.(1977)

Improved surfactant flooding

Alkali metal carbonate

complex mixtures of aryl sulfonates and alkaryl sulfonates

-

Preflush solution of sodium sulfate,

IFT reduction

PA, PS, or copolymers of acrylamide

Wettability change in  predominantly oil-wet formations

Ionic PS B1459

Using initiation slug having alkaline agent

Injecting

Protecting PA from

 biopolymer after surfactant slug and

degradation due to salts or surfactants in the formation.

 phosphate and carbonate Burdyn et al.(1977 )

Chang (1980)

Sulfonate surfactant (alkyl aryl sulfonate)

-

Sodium hydroxide

Surfactant-

Any compatible water

-

-

 polymer flooding

external surfactant system

Alkali-surfactantwater flooding

 before PA Yen &

Enhanced alkali-

A mixture of native

Farmanian (1980)

water flooding

 petroleum surfactants obtained by distilling  petroleum and mixed with

-

Sodium

-

orthosilicate

Isolation of native  petroleum surfactants for IFT reduction in aqueous-alkaline

original petroleum or

systems

enriched with residue Carlin et al. (1980)

Surfactant flooding

A mixture of petroleum sulfonates

Ethoxylated alkyl or alkylaryl

-

PA or PS

Disclosing a novel aqueous surfactantcontaining fluid

-

Emulsion eliminated the need for a separate

Making stable microemulsion over a wide range of temperatures,

 polymer slug

salinities, and hardness

Using PA in the slug if it’s compatible with surfactant

Making stable emulsion over a wide range of temperatures, salinities, and hardness

compounds Shupe & Maddox (1981)

Cardenas et al.(1981)

Surfactantcontaining emulsion flooding

Surfactant flooding

Polyethoxylated alkylphenol nonionic surfactant

An alkylpolyalkoxyalkylene sulfonate or alkylarylpolyalkoxyalkylene sulfonate

Polyethoxylated aliphatic alcohol (including alkanols)

-

-

and reservoir temperature

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Chemical Aspects of Surfactant-based EOR

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(Table 1) Contd…..

Inventor(s)

EOR Method

Surfactant

Cosurfactant

JohnsonWestmoreland (1981)

Surfactantenhanced chemical EOR

Organic sulfonate surfactants

Alcohol cosurfactants

Alkali or Other Additives

-

Polymer

PA or PS

Method Approach and/or Novelty

Synthesizing a sacrificial adsorbate inhibiting the adsorption of surfactant

Alford & Hardman

Surfactant flooding

 Neutralized air-oxidized solvent extracted oil

-

-

from 2 to 8 carbon atoms

(1984) Watson & Butler (1984)

Mixture of alkanols having

-

-

-

Emulsifier system is operable over a wide range of salinities

-

-

A method to produce  petroleum sulfonates  by processing crude oil adjacent the well site

Lipowski & Miskel (1985)

Enhanced water flooding using  polymer emulsion

Blends of low HLB and high HLB surfactants used as an emulsifier

-

-

-

Optimizing amphoteric water-in-oil selfinverting polymer emulsion

Balzer (1986)

Tenside flooding of reservoirs of medium and high

Use of carboxymethylated oxethylates as tensides

-

-

"Cellobond" HEC 100 000 A in the

Reducing tenside retention

salinities

Dilgren (1986)

Gregory (1989)

mobility  buffer

Injecting steam and surfactantcontaining steam-

Anionic, sodium dodecylbenzene sulfonate, olefin sulfonate

foam-forming components

surfactants

Cosurfactant

-

enhanced alkali flooding for anhydrite formations Borchardt (1989)

Steam foam EOR for rapid build-up of pressure

-

-

-

Process for selecting a steam foam forming surfactant

Disulfonated diphenyl ether or Alphaolefin

Sodium hydroxide

Flocon 4800, a  polysaccharide  broth polymer

Adding an alkali metal sulfate or ammonium sulfate to maintain pH

-

-

-

Initial injection of a rapidly-foaming surfactant

-

-

-

Reducing surfactant loss by alkali metal carbonate or  bicarbonate salt

sulfonates

Internal olefin sulfonate, a vinylidene olefin sulfonate, or secondary alkane sulfonate

Falls (1989)

Surfactantenhanced CO 2 flooding

An anionic sulfonate surfactant, Enordet.RTM. alcohol ethoxy glycerol sulfonates (AEGS)

solubilized in water especially surfactants which exhibit low solubility in water.” YeSung and SungNan [55] provided an improved concentrated surfactant formulation containing a mixture of anionic surfactants (particularly the anionic surfactants formed from the sulfonates of linear and branched alkyl  benzenes, and the sulfonates sulfona tes of alkyl naphthalenes, naphtha lenes, toluene, toluene , xylene, and petroleum sulfonates and their metal and amine salts) which demonstrate ultra-low (<10-2 mN/m) interfacial

tension against crude oils-containing acidic organic components- over a broad range of surfactant, electrolyte, and alkali concentrations, and temperatures. Moreover, authors added that [55]:” when this chemical combination is added to the alkaline brine, provide ultra-low (<10-2  mN/m) interfacial tension against a crude oil. They also cited that the above-discussed formulation may comprise solvent(s) and nonionic cosurfactant(s) which can enhance the ultra-low -2 (<10   mN/m) interfacial tension in the injected fluid”. The authors also provided some details on how to add an aqueous

8  Recent Patents on Chemical Engineeri ng, 2009 , Vol. 2, No. 1

Benyamin Yadali Jamaloei

 polymer to increase the viscos ity of the inject ion fluid . It wa s also expounded that the alkali comes in contact with the trapped oil and forms salts having surfactant properties which enable the residual oil to be emulsified or dispersed in the aqueous phase thereby being mobilized to the surface.” Berger, et al. [56] formulated a composition of surfactants containing a weak and a strong anionic functionality group, into a concentrated surfactant blend. The concentrated surfactant blend contained an aqueous solvent such as water or brine, and a cosurfactant/solvent such as a lower molecular weight alcohol or alcohol ether. The concentrated surfactant blend was added in a concentration range of about 0.05-5% to the injection brine and introduced into the formation [56]. Shpakoff and Raney [57] filed for a patent wherein a method of treating a hydrocarbon formation was described. The method included injecting a chemical composition (including an aliphatic anionic surfactant and an aliphatic nonionic additive) into the hydrocarbon formation that would interact with the omnipresent hydrocarbon. A novel method of recovering crude oil from a hydrocarbon formation was proposed by Berger, et al. [58]. Table 2.

This method included injecting an aqueous solution containing an effective amount alkali metal, alkaline-earth or ammonium salts of alcohol ether sulfonates derived from unsaturated alcohol ethers. The unsaturated alkoxylated alcohol contained various amounts of ethylene oxide,  propylene  propy lene oxide and butylene butylen e oxides elected to optimize optimiz e their interfacial properties with different types of crude oil with different brines [58]. Campbell and Sinquin [59] filed for a patent to introduce alkylxylene sulfonate for enhanced oil recovery processes. The alkylxylene moiety in the alkylxylene sulfonate contained a high percentage of the 4-alkyl-1,2-dimethyl  benzene isomer and alkyl group attachment to the xylene ring at positions higher than the 2-position on the alkyl carbon chain. Moreover, authors discussed the method for enhancing the recovery of oil from a reservoir that employs the alkylxylene sulfonate of the presented invention [59]. In Table 2, summary of some important (in terms of  presenting more novelties) patents from 1990 to 2008 has  been given in wh ich the emphasis em phasis is on the rendered ren dered novelty in each work.

Summary of Some Important Patents from 1990 to to 2008 in Surfactant-ba sed Chemical EOR

Inventor(s)

EOR Method

Surfactant

Cosurfactant

Loza & Cyngier (1990)

Surfactant flooding

C-branched zwitterionic

Maddox (1990)

Surfactant-polymer flooding

Modified sulfonate surfactant

Optional

Loza et al. (1990)

Surfactant flooding

Divalent ion tolerant aromatic sulfonates

Balzer (1990)

Surfactant-polymer flooding

Pinschmidt & Lai (1990)

Enhanced water flooding

Alkali or Other Additives

Polymer

Method Approach and/or Novelty

Optional thickener to increase the viscosity of the  buffer slug

Developing a novel C branched zwitterionic surfactant for wettability change and IFT reduction

Adding solubilizer to polymer drive to allow high salinity  brine in polymer drive

-

Modifying sulfonate systems to permit use of fluids of increased salinity in the polymer drive

-

-

-

Alky/aryl alcohols having  been sulfonated

Mixture of a carboxymethylated oxethylate and a polyglucosyl sorbitol

A monohydric or polyhydric alcohol or an alkyl ester of a  polyhydric alcohol

-

Polymer Flocon 4800 (xanthan, Pfizer)

Optimizing a slug for reservoirs with marked temperature fluctuations

-

-

Injecting unhydrolyzed  poly(N-vinylamide)

-

High molecular weight  polyvinylamine formed insitu

Lau & Borchardt (1990)

Gas foam flooding

Surfactant enriched in olefin disulfonate

-

Sodium chloride to enhance the formation of a foam

-

Providing a foam of comparable strength and  propagation

Schramm et al. (1991)

Gas foam floodinga foam that imbibes and transports oil

Fluorad FC751 surfactants

-

-

-

Selecting surfactantcontaining foam using micro-visualization techniques

2009, Vol. 2, No. 1 Recent Patents on Chemical Engineering, 2009, Vol.

Chemical Aspects of Surfactant-based EOR

9

(Table 2) Contd….

Inventor(s)

EOR Method

Surfactant

Cosurfactant

Kissel (1991)

Enhanced low tension water flooding for relatively viscous

If organonitrogen compounds having surfactant properties used as the cationic salt-forming

-

oils

moiety, surfactants can be formed in the water phase

-

-

Bloodworth et al.

Alkali or Other Additives

-

Polymer

-

Method Approach and/or Novelty

Injecting a safe form of carbon disulfide comprising salts of triand tetrathiocarbonic acid

-

-

-

Synthesis of new cleavable surfactants and their use for the

(1992)

 preparation of emulsions Prukop (1992)

Surfactant flooding

Alkoxylated nonionic or

-

-

-

ionic surfactant

Developed for heavy oil reservoirs

Current (1992)

Surfactant flooding

One anionic and one nonionic surfactant component

-

-

-

Using surfactant compositions for improved oil mobility

DiLullo et al. (1992)

Producing and transporting crude  petroleum as a dispersion of oil in

-

-

Dispersant is selected from alkali metal or ammonium salts

-

Recovering highly viscous petroleum  products to flow by an aqueous dispersion of

water admixed with the dispersant.

of organic sulfonates

the petroleum product

Prukop (1995)

-

-

-

-

-

A method for recovering surfactants from produced fluids

Keys (1999)

Surfactant flooding  by use of stable monophasic liquid compositions

Cationic, anionic, amphoteric , and nonionic alone or in mixture

-

-

-

Solubilize increased amount of surfactant for foam stabilizing

Yesung & Sungnan (2000)

Alkali-surfactant polymer flooding

Mixture of anionic surfactants

 Nonionic

Sodium hydroxide

-

Optimizing chemical solution

Berger (2006)

Surfactant-

Surfactants having

Ethylene glycol

Sodium hydroxide

Optional

Injecting an aqueous

enhanced chemical EOR

carboxylic, and sulfonate or sulfate functionalities

Monobutyl ether

or sodium carbonate

Surfactant-based chemical flooding

An aliphatic anionic surfactant

An aliphatic nonionic additive

-

Shpakoff & Raney (2007)

fluid containing a bifunctional surfactant Pre polymer solution

Optimizing hydrocarbon recovery composition

ALCOFL OOD.RT M. Berger et al. (2008)

Surfactant flooding

A solution containing an effective amount alkali

Optional

Optional

Optional

metal, alkaline-earth or ammonium salts of alcohol ether sulfonates derived

Developed for reservoir with high temperature, salinity and divalent cations concentration.

from unsaturated alcohol ethers Campbell & Sinquin (2008)

Surfactant flooding

Pure alkylaryl sulfonates

Optional

-

-

Slug optimization to recover light crude oils

10

 Recent Patents on Chemical Engineering,

2009 ,

Vol. 2, No. 1

CURRENT & FUTURE DEVELOPMENTS

As was shown in the patent survey of all decades, chemistry of chemical slug design and formulation has been of particular concerns from early patents to this date. By focusing on the chemistry of chemical flood processes, it would be viable to dramatically reduce the operating cost of a desired chemical field operation. The technical and patent literature contains a number of surfactant slug designs formulated to mobilize residual oil. Discussed patents contained a variety of techniques that are used to screen surfactant slugs for use as potential oil recovery agents. Importantly, patents’ focus has been continuously on discovering new and relatively economic surfactants and other chemicals with gentle interfacial tension reducing  property and also stability /compatibi lity under fluctuat ing/ harsh conditions (temperature/salinity) of petroleum reservoirs underground. To achieve these goals, intensive research has been conducted over the past several decades for the synthesis of novel chemicals, including mostly alkali and surfactants, and envisioning their efficient manipulation in a specific surfactant-based chemical flooding process. In addition, research has been continuously carried out to introduce novel surfactant-based chemical EOR processes to make avail of the novel synthesized chemical systems (surfactant or alkaline systems). Since most of the novel synthesized chemical systems may require a special modification of the present chemical EOR processes so that to be effective in given circumstances within a petroleum reservoir. To conclude, research will be continuously carried out in order to design cost-effective chemical slugs whereby to increase the chance of application of such processes in field scale which requires, at first, an economic viability. This would be allotted to this fact that, evaluations to determine which chemical slug offers the best economics for a specific field application are often complex since an infinite array of chemical variables must be considered for this evaluation task. Synthesis, screening, and manipulation of different appropriate chemicals, and their combinations for oil recovery efficiency purposes, will constitute an active field of future research in the area of chemical flooding. Stability of formulated chemical slugs (systems or solutions) in harsh conditions existing underground within hydrocarbon formations, and their compatibility with porous medium, and formation fluids will still remain another challenging issue which would inspire the academic and industrial research environment for future works. Finally, designing innovative forms of chemical flooding or modifying and revamping the existing chemical methods of hydrocarbon recovery will draw growing attentions of researchers as an active area of future research activities. activities. CONFLICT OF INTEREST

I, Benyamin Yadali Jamaloei, the author of this manuscript entitled “Insight into the Chemistry of Surfactant-based tant-based Enhanced O il Recovery Processes” certify that no financial support or contribution has been made by any research institute/organization or individual during

Benyamin Yadali Jamaloei

 preparatio n and completion compl etion of this manuscript. manuscr ipt. I also assert that no contribution to the submitted work was made by any individual during the process of research, data gathering, analysis, and m anuscript preparation. REFERENCES

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