Multivariate Optimization of Surfactant Systems for Tertiary Oil Recovery

1981 ◽  
Vol 21 (01) ◽  
pp. 77-88 ◽  
Author(s):  
James E. Vinatieri ◽  
Paul D. Fleming
Keyword(s):  
Oil Recovery ◽  
Degrees Of Freedom ◽  
Multivariate Optimization ◽  
Phase Rule ◽  
Two Degrees Of Freedom ◽  
Number Of Components ◽  
Petroleum Sulfonate ◽  
Three Phase ◽  
Tertiary Oil Recovery ◽  
Surfactant Systems

Abstract A new method of optimization has been developed for tertiary oil recovery systems employing surfactants. This method simultaneously adjusts all composition variables in a manner which greatly reduces the total number of compositions which need to be investigated experimentally. This multivariate optimization technique has been applied to two petroleum sulfonate systems, one containing a pure hydrocarbon and the other containing a crude oil. In both cases, significant reductions of interfacial tensions were achieved relative to those obtained by conventional optimization with respect to salinity alone. Surfactant systems for tertiary oil recovery commonly involve at least five components: oil, water, surfactant, cosurfactant, and electrolyte. The optimization of such systems is hindered by this large number of components and because interpolation of behavior is often difficult. Previously, such systems have been optimized by adjusting concentrations of individual components empirically. These empirical optimizations have indicated that surfactant systems which form three phases are preferred for oil recovery although they are not necessarily fully optimized. As stated by the Gibbs phase rule, a five-component, three-phase system has only two degrees of freedom at constant temperature and pressure. These two degrees of freedom can be identified mathematically by making use of chemical analysis of a three-phase sample. Thus, optimization of three-phase surfactant systems can be accomplished by adjusting only two variables, resulting in a dramatic reduction of time and effort required to optimize such systems. For the systems studied, both the volume per unit mass of surfactant and the viscosity of the microemulsion phase are increased significantly even though the optimization was based on interfacial tension only. These bonuses should lead to improved sweep efficiency in the displacement process. Introduction Surfactant systems have received much attention recently as a means for increasing the recovery of oil from a subterranean reservoir.1–5 Typically, these systems employ a petroleum sulfonate as the surfactant and an alcohol as a cosurfactant or co solvent. Thus, when the oil and brine (water plus electrolyte) also are considered, these oil recovery systems are seen to contain at least five components. Because of the high cost of surfactant systems, it is important that any such system be optimized to provide the greatest oil recovery at the lowest cost. Unfortunately, this optimization is hindered by, at least, these three factors:the large number of components and the correspondingly large number of possible compositions which must be evaluated,interactions between components which make interpolation of behavior difficult, andthe relative difficulty of performing displacement tests in porous media.

Correlation of Emulsion Stability With Phase Behavior in Surfactant Systems for Tertiary Oil Recovery

1980 ◽  
Vol 20 (05) ◽  
pp. 402-406 ◽  
Author(s):  
James E. Vinatieri
Keyword(s):  
Phase Behavior ◽  
Oil Recovery ◽  
Emulsion Stability ◽  
Equilibrium Phase ◽  
Phillips Petroleum ◽  
The North ◽  
Three Phase ◽  
Tertiary Oil Recovery ◽  
Surfactant Systems ◽  
Oilfield Operations

Abstract This paper describes a study of the emulsions which could occur during a pilot surfactant flood, such as that conducted by Phillips Petroleum Co. in the North Burbank Unit, Osage County, OK. The phase behavior of this surfactant system can be characterized by three types of microemulsions, with the transition from one type to another being a function of the salinity. The rate at which emulsions coalesce was seen to correlate directly with the type of microemulsion. Coalescence was slow for macroemulsions at low salinities, rapid at intermediate salinities (where the final state was a three-phase system), and varied from slow to rapid at salinities above the three-phase region. Knowledge of the correlation between phase behavior and emulsion stability can be useful in treating macroemulsions produced during a surfactant flood. Introduction With the increased emphasis currently being placed on the use of surfactants for tertiary oil recovery, a potential problem exists with emulsions which can be produced as a consequence of a surfactant flood. For example, if a channeling problem between an injection well and a production well should occur, it may be possible to produce relatively large amounts of surfactant at moderately high concentrations (0.2 to 2.0070). Under these conditions, emulsions of oil and brine could be stabilized by the presence of the surfactant and could pose a serious problem. Although these emulsions are thermodynamically unstable and ultimately should separate into bulk oil and water phases, the presence of surfactants can increase greatly the time required for such separations. Typical oilfield operations allow, at most, several hours for this separation of phases to occur, but some emulsions containing surfactants may require weeks or even months to separate. Thus, a definite need exists for being able to accelerate this coalescence process. Phillips Petroleum Co. is conducting a pilot surfactant flood in the North Burbank Unit (NBU) in Osage County.1,2 The work reported here was directed at developing a contingency plan for breaking emulsions which may be produced by this surfactant flood. The problem of studying emulsions produced by a surfactant flood has two aspects:the nature of the phases which result when thermodynamic equilibrium finally is attained andthe rate at which this equilibrium state is reached. This is not to imply that any emulsion can be described completely by characterization of these two properties but rather that these are the two properties most important to oilfield operations and, hence, form the basis for the work reported here. The next section discusses the equilibrium properties of surfactant systems and the one following discusses the coalescence of emulsions. The fourth section describes the use of chemical demulsifiers to accelerate coalescence. Equilibrium Phase Behavior The equilibrium phase behavior of systems of oil and water containing appreciable amounts of surfactant (i.e., 0.5%) is characterized by the presence of microemulsions.1,3-5 These microemulsion phases have a high degree of structure and may contain large amounts of both oil and water.

Importance of lignosulfonates in petroleum recovery operations

1981 ◽  
Vol 59 (13) ◽  
pp. 1938-1943 ◽  
Author(s):  
Graham Neale ◽  
Vladimir Hornof ◽  
Christopher Chiwetelu
Keyword(s):  
Crude Oil ◽  
Oil Recovery ◽  
Phase Behaviour ◽  
Oil Fields ◽  
Potential Importance ◽  
Mixed Surfactant ◽  
Interfacial Tensions ◽  
Mixed Surfactant Systems ◽  
Petroleum Sulfonate ◽  
Surfactant Systems

This paper reviews the potential importance of aqueous lignosulfonate solutions in the recovery of petroleum from existing partially depleted oil fields. The surfactant qualities of lignosulfonates are described and their ability to interact synergistically with petroleum sulfonate surfactants (which are currently popular in the industry) to produce ultra-low interfacial tensions with crude oil is discussed. The phase behaviour characteristics and oil recovery efficacies of these mixed surfactant systems are also examined.

Optimal Injection Policies for Enhanced Oil Recovery: Part 2-Surfactant Flooding

1984 ◽  
Vol 24 (03) ◽  
pp. 333-341 ◽  
Author(s):  
Zohreh Fathi ◽  
Fred W. Ramirez
Keyword(s):  
Oil Recovery ◽  
Return On Investment ◽  
Volumetric Flow Rate ◽  
Commercial Application ◽  
Type B ◽  
Surfactant Flooding ◽  
Tertiary Oil Recovery ◽  
Optimal Injection ◽  
Surfactant Systems ◽  
The Cost

Abstract The optimal control theory of distributed-paranieter systems has been applied to the problem of determining the best injection policy of a surfactant slug for a tertiary oil recovery chemical flood. The optimization criterion is to maximize the amount of oil recovered while minimizing the chemical cost. A steepest-descent gradient method was used as the computational approach to the solution of this dynamic optimization problem. The performance of the algorithm was examined for the surfactant injection in a one-dimensional flooding problem. Two types of interfacial tension (IFT) behavior problem. Two types of interfacial tension (IFT) behavior were considered. These are a Type A system where the IFT is a monotonically decreasing function with solute concentration and a Type B system where a minimum IFT occurs at a nominal surfactant concentration. For a Type A system, the shape of the optimal in 'faction strategy was not unique, however, there is a unique optimum for the amount of surfactant needed. For a Type B system, the shape of the optimal injection as well as the amount injected was unique. Introduction Surfactant recovery systems are being investigated by the petroleum industry as a means of increasing the petroleum supply. Commercial application of any petroleum supply. Commercial application of any surfactant flooding process relies upon economic projections that indicate a decent return on investment. projections that indicate a decent return on investment. Previously. surfactant systems for tertiary oil recovery have been optimized by adjusting concentrations of individual components empirically. Salinity has been shown to be an important variable in surfactant system optimization. The particular choice of surfactant and cosurfactant has been studied by Salager et al. Multivariable optimization of surfactant systems based on minimizing the IFT has been studied by Vinatiere et al. As reported, such an optimization may or may not coincide with optimal oil recovery since low IFT is a necessary. but not a sufficient condition for achieving, high displacement efficiency. Chemical supply and cost are important parts of economic projections. Because of the high cost of chemicals, it is essential to optimize surfactant systems to provide the greatest oil recovery at the lowest cost. In this paper, an optimization surfactant is taken as the minimization of the chemical cost and maximization of the recovered oil. The goal is to determine the best way of injecting a surfactant slug into the reservoir formation. Mathematical Formulation of the Performance Index Performance Index We desire to obtain maximum oil recovery with a minimum amount of chemical surfactant injected. These objectives can he expressed in a quantitative form through the formulation of a cost functional. J', which is to be minimized, where J' equals the cost of surfactant injected minus the value of oil recovered. This descriptive statement of the cost functional must be translated into a mathematical form to use quantitative optimization techniques. The oil value can be formulated as (1) where C1 = cost of oil per unit volume ($251.6/m 3[$40/bbl]),= volumetric flow, rate of oil at the coreoutlet L = core length, and a = time. The chemical cost is expressed mathematically as (2) where C2 = chemical cost per unit weight ofsurfactant ($5.45 × 10–3/g [$2.47/lbm]), Cs( ) = surfactant concentration of the injectedfluid in weight fraction, P slug = slug density ( 1 g/cm 3 ). and Qw, ( ) = volumetric flow rate of water at thecore inlet. The objective functional is, therefore, (3) JPT P. 333

The Rules for Achieving High Solubilization of Brine and Oil by Amphiphilic Molecules

1983 ◽  
Vol 23 (02) ◽  
pp. 327-338 ◽  
Author(s):  
M. Bourrel ◽  
C. Chambu
Keyword(s):  
Oil Recovery ◽  
Water Phase ◽  
Phase System ◽  
Middle Phase ◽  
Rich Phase ◽  
Optimal State ◽  
Amphiphilic Molecules ◽  
Three Phase ◽  
Surfactant Systems ◽  
Formulation Variables

Abstract The oil-recovery effectiveness of a chemical flood has been proved related to the phase behavior of the brine/oil/surfactant system. In particular, it is advantageous to formulate the system so that optimal threephase behavior is obtained. However, it also has been demonstrated that all the optimized systems are not equivalent in terms of solubilization. interfacial tensions (IFT's), and oil-recovery efficiency. This paper addresses the conditions that promote high solubilization in microemulsions, a property correlated to the values of the IFT and therefore correlated to the ability of such systems to displace the oil in porous media. When one formulation parameter is changed, another parameter must be varied at the same time for compensation to reoptimize the system. The mechanism of solubilization is investigated experimentally by considering the usual formulation parameters: salinity, oil type, alcohol type and concentration, and surfactant structure and type (anionics and nonionics). The results are interpreted in terms of interaction energies between surfactant, oil, and water. In particular, the role of the alcohol and its impact on the solubilization by amphiphilic systems are discussed in detail and interpreted. Moreover, the concepts developed in this paper explain the effect of the surfactant structure and therefore aid in the design of amphiphilic molecules exhibiting a high solubilizing power for given conditions of brine, temperature, etc. Introduction Mobilization and transport of residual oil by chemical-flooding processes involve various mechanisms that must be considered when formulating a surfactant slug, but, among them, it is well known that IFT's between phases play a major role. Reed and Healy have shown phases play a major role. Reed and Healy have shown that ultralow IFT's can be attained when a microemulsion phase (surfactant-rich phase, the so-called "middle phase (surfactant-rich phase, the so-called "middle phase") is in equilibrium simultaneously with an oil phase") is in equilibrium simultaneously with an oil phase and a water phase. They first have defined the phase and a water phase. They first have defined the concept of optimal salinity as being the point where the IFT's at the oil-middle phase and middle phase/water interfaces are equal. At that point, the volumes of oil and water solubilized in the middle phase generally are identical, although there is no theoretical basis for that. A correlation between the values of the quantities of oil and water solubilized in the middle phase and the values of the IFT's between the phases also has been found: the lower the tension, the higher the solubilization. Therefore, it appears judicious to start the screening procedure of surfactant systems for enhanced oil procedure of surfactant systems for enhanced oil recovery (EOR) by looking for the point where equal volumes of oil and water are solubilized in the surfactant phase of a three-phase system. During recent years, phase of a three-phase system. During recent years, much time has been devoted to discovering that point, and the rules for compensating changes in the formulation variables have been established for anionic and non-ionic surfactants. We must emphasize that, if we start from an optimized system and we change a formulation variable defining the system, the optimal state is lost, and another formulation variable must be changed to reach a new optimal state. All optimized systems are not equivalent, as shown in previous results, and consideration of the amount of previous results, and consideration of the amount of oil and water solubilized in such systems provides a criterion to compare them. In a previous paper, we carried out a systematic study of the effect of the formulation variables on the solubilization at optimum by anionic surfactants. Some results concerning nonionics have been presented recently presented recently. SPEJ p. 327

The Effect of Ethoxylated Sulfonates on Salt Tolerance and Optimal Salinity of Surfactant Formulations for Tertiary Oil Recovery

1978 ◽  
Vol 18 (03) ◽  
pp. 167-172 ◽  
Author(s):  
V.K. Bansal ◽  
D.O. Shah
Keyword(s):  
Salt Tolerance ◽  
Interfacial Tension ◽  
Oil Recovery ◽  
Surfactant Concentration ◽  
Weight Percent ◽  
Mixed Surfactant ◽  
Optimal Salinity ◽  
Petroleum Sulfonate ◽  
Ethoxylated Alcohols ◽  
Tertiary Oil Recovery

Abstract The addition of an ethoxylated sulfonate (EOR-200) and its effect on the salt tolerance and optimal salinity of formulations containing a petroleum sulfonate (TRS 10-410 or Petrostep-465) petroleum sulfonate (TRS 10-410 or Petrostep-465) and an alcohol was investigated. When salt concentration increases, the mixed surfactant formulations undergo the following changes: isotropic, birefringent, phase separation. The salt concentration required for phase separation increased with the fraction of the ethoxylated sulfonate in the formulation. When mixed surfactant formulations were equilibrated with an equal volume of oil (decane or hexadecane) a middle-phase microemulsion formed in a specific salinity range. The optimal salinity increased with the fraction of the ethoxylated sulfonate in the mixed surfactant formulations. At optimal salinity as high as 32-percent NaCl, these surfactant formulations exhibited ultra-low interfacial tension (10-2 to 10-3 dynes/cm). These formulations also showed that an increase in the solubilization parameter decreases the interfacial tension. parameter decreases the interfacial tension Introduction The potential use of petroleum sulfonates for tertiary oil recovery has been discussed and several patents have been issued during the past two decades. The solubilization, phase behavior and interfacial tension of petroleum sulfonates have been studied. Petroleum sulfonates are known to exhibit relatively low salt tolerance and a low value of optimal salinity (1- to 2-percent NACl). Dauben and Froning studied the effect of Amoco Wellaid 320 (ethoxylated alcohol) on a surfactant formulation that was primarily a petroleum sulfonate. They observed that surfactant formulations prepared using ethoxylated alcohols as cosurfactants exhibited improved temperature stability and were less sensitive to salts, compared with formulations prepared with isopropanol as a cosurfactant. Several prepared with isopropanol as a cosurfactant. Several patents were issued on the possible use of patents were issued on the possible use of ethoxylated alcohols and ethoxylated sulfonates in oil recovery formulations. This study reports the effect of blending an ethoxylated sulfonate (EOR-200) with a petroleum sulfonate (TRS 10-410 or Petrostep-465) on various properties of the mixed surfactant formulations (for properties of the mixed surfactant formulations (for examples, salt tolerance, optimal salinity, interfacial tension, and solubilization). MATERIALS AND METHODS Petroleum sulfonates TRS 10-410 and Petrostep-465 were supplied by Witco Chemicals and Stepan Petrostep-465 were supplied by Witco Chemicals and Stepan Chemicals, respectively. Ethoxylated sulfonate EOR-200 was supplied by Ethyl Corp. Paraffinic oils (n-hexadecane and n-decane) as well as 99-percent pure isobutanol and n-pentanol were purchased from Chemicals Samples Co. All purchased from Chemicals Samples Co. All surfactants were used as received. The average equivalent weight of TRS 10-410 and Petrostep-465 was 420 and 465, respectively, and the activity of surfactants was approximately 60 percent (as reported by the manufacturers). The molecular weight of EOR-200 was given as 523 by Ethyl and the sample contained 25.3 weight percent active solid surfactant. Aqueous solutions composed of Petrostep-465 (5 percent) and n-pentanol (2 percent) were prepared on the basis of weight. Aqueous surfactant solutions were equilibrated with the same volume of n-decane. Optimal salinity values were obtained using the approach described by Healy and Reed. The effect of EOR-200 on the properties of mixed surfactant formulations was studied by gradually replacing Petrostep-465 with EOR-200 and keeping the total surfactant concentration constant at 5 weight percent. Another surfactant formulation studied was composed of TRS 10-410 (5 percent) and IBA (3 percent). Optimal salinity was determined using percent). Optimal salinity was determined using n-hexadecane. TRS 10-410 was replaced gradually by EOR-200, keeping the total surfactant concentration constant at 5 weight percent. The systems studied are tabulated in Table 1. SPEJ P. 167

The Use of Pseudocomponents in the Representation of Phase Behavior of Surfactant Systems

1979 ◽  
Vol 19 (05) ◽  
pp. 289-300 ◽  
Author(s):  
J.E. Vinatieri ◽  
P.D. Fleming
Keyword(s):  
Phase Diagram ◽  
Phase Behavior ◽  
Oil Recovery ◽  
Dimensional Space ◽  
Multicomponent Systems ◽  
Tertiary Oil Recovery ◽  
Oil Water ◽  
Surfactant Systems ◽  
Lower Dimensional ◽  
Water Alcohol

Abstract A new method is developed to represent the phase behavior of multicomponent systems. This method uses fewer pseudocomponents than true components, but unlike conventional methods in which pseudocomponents are often chosen arbitrarily, the pseudocomponents are often chosen arbitrarily, the method uses regression analysis to find a "best" set of pseudocomponents.The method is applied to two surfactant systems of the type used for tertiary oil recovery. One system contains a crude oil (from the North Burbank Unit, Osage County, OK) and the other contains a pure hydrocarbon, 1-phenyltetradecane. For both systems the representation in terms of the pseudocomponents chosen by the regression analysis is significantly more faithful than that obtained by conventional methods.Since the considerations discussed here are general, they should be applicable to a wide range of phase studies in multicomponent systems. For example, they should be illuminating when applied to oil recovery by gas injection (carbon dioxide, natural gas, etc.), and to extraction processes, as well as to surfactant systems. Introduction Systems containing surface active agents have attracted a great deal of attention in connection with tertiary oil recovery. In many of these systems optimum oil recovery has been found to be strongly correlated with the phase behavior of these systems. To understand completely the basis for these correlations, one must be able to represent the phase behavior of systems containing surfactants adequately.Surfactant systems for tertiary oil recovery usually contain at least five components: oil, water, surfactant. cosurfactant, and electrolyte. The isothermal, isobaric phase diagram of these systems can be represented in a phase diagram of these systems can be represented in a four-dimensional space. Because physical representation (in three dimensions) of such a diagram is impossible. various techniques have been developed to attempt to represent the phase behavior in lower dimensional spaces. All these techniques correspond to projections of the original diagram onto lower dimensional spaces. Although almost unlimited methods of projection exist, only a small fraction convey useful information.Two projection schemes having some similarities but different intents and consequences are straight mathematical projection and "pseudocomponent" projection. Straight mathematical projection refers to the process of directly projecting the four-dimensional data for the entire phase diagram along some specified direction onto a three-dimensional space. All information parallel to the direction of the projection is lost. For example, if the rays of projections are parallel to the oil/water edge of the phase diagram, the resulting representation contains no information about the relative amounts of oil and water in the phases. In principle, this problem can be circumvented by generating two representations corresponding to projections of the same data along two different directions. For example. a second representation could be produced corresponding to a projection parallel to the water/alcohol edge of the phase diagram. parallel to the water/alcohol edge of the phase diagram. Although neither representation contains complete information, the pair of representations does contain all information about the system. The problem with this method is that the information is not perceived easily and, since the intent of using phase diagrams is usually to make visible a summary of the phase trends, such mathematical representations are not very useful.The second and generally more useful projection scheme uses pseudocomponents. A pseudocomponent is some mixture of pure components treated as a single component. SPEJ P. 289

Investigation of Three-Phase Regions Formed by Petroleum Sulfonate Systems

1981 ◽  
Vol 21 (05) ◽  
pp. 581-592 ◽  
Author(s):  
Creed E. Blevins ◽  
G. Paul Willhite ◽  
Michael J. Michnick
Keyword(s):  
Interfacial Tension ◽  
Phase Behavior ◽  
Oil Recovery ◽  
Phase Region ◽  
Phase Boundaries ◽  
Middle Phase ◽  
Optimal Salinity ◽  
Petroleum Sulfonate ◽  
Recovery Processes ◽  
Three Phase

Abstract The three-phase region of the Witco TRS 10-80 sulfonate/nonane/isopropanol (IPA)/2.7% brine system was investigated in detail. A method is described to locate phase boundaries on pseudoternary diagrams, which are slices of the tetrahedron used to display phase boundaries of the four-component system.The three-phase region is wedge-like in shape extending from near the hydrocarbon apex to a point near 20% alcohol on the brine/alcohol edge of the tetrahedron. It was found to be triangular in cross section on pseudoternary diagrams of constant brine content, with its base toward the nonane/brine/IPA face. The apex of the three-phase region is a curved line where the M, H + M, and M + W regions meet. On this line, the microemulsion (M*) is saturated with hydrocarbon, brine, and alcohol for a particular sulfonate content. A H + M region exists above the three-phase region, and an M + W region exists below it.Relationships were found between the alcohol concentration of the middle phase and the sulfonate/alcohol and sulfonate/hydrocarbon ratios in the middle phase. These correlations define the curve that represents the locus of saturated microemulsions in the quaternary phase diagram. Alcohol contents of excess oil and brine phases also were correlated with alcohol in the middle phase.Pseudoternary diagrams for sulfonates are presented to provide insight into the evolution of the three-phase region with salinity. Surfactants include Mahogany AA, Phillips 51918, Suntech V, and Stepan Petrostep(TM) 500. Differences between phase diagrams follow trends inferred from comparisons of equivalent weights, mono-/disulfonate content, optimal salinity, and EPACNUS values. Introduction The displacement of oil from a porous rock by microemulsions is a complex process. As the microemulsion flows through the rock, it mixes with and/or solubilizes oil and water. The composition of the microemulsion is altered by adsorption of sulfonate, leading to expulsion of water and/or oil. Multiphase regions are encountered where phases may flow at different velocities depending on the fluid/rock interactions. Knowledge of phase behavior of microemulsion systems is required to understand the displacement mechanisms, to model process performance, and to select suitable compositions for injection.Microemulsions used in oil recovery processes consist of five components: oil, water, salt, surfactant (usually a petroleum sulfonate and a cosurfactant (usually an alcohol). Brine frequently is considered to be a pseudocomponent. When this assumption is valid, a microemulsion may be studied as a four-component system.Windsor developed a qualitative explanation and classification scheme for microemulsion phase behavior. Healy and Reed showed that Windsor's concepts were applicable to microemulsions used in oil recovery processes. Healy et al. introduced the concept of optimal salinity to define a particular characteristic of surfactant system. The optimal salinity for phase behavior was defined as the salinity where the middle phase of a three-phase system has equal solubility of oil and brine. They also found that optimal salinity determined in this manner was close to the salinity where the interfacial tension between the upper and middle phases was equal to the interfacial tension between the middle and lower phases.Salager et al. developed a correlation of optimal salinity data for a particular surfactant. SPEJ P. 581^

Phase Behavior Studies of Two Model Surfactant Systems

1982 ◽  
Vol 22 (01) ◽  
pp. 53-60 ◽  
Author(s):  
William J. Benton ◽  
Natoli John ◽  
Syed Qutubuddin ◽  
Surajit Mukherjee ◽  
Clarence M. Miller
Keyword(s):  
Aqueous Solutions ◽  
Phase Boundary ◽  
Phase Behavior ◽  
Oil Recovery ◽  
Develop Model ◽  
Middle Phase ◽  
Lower Phase ◽  
Interfacial Tensions ◽  
Petroleum Sulfonate ◽  
Surfactant Systems

William J. Benton, Carnegie-Mellon U. John Natoli, Carnegie-Mellon U. Qutubuddin, Syed SPE, Carnegie-Mellon U. Mukherjee, Surajit, Carnegie-Mellon U. Miller, Clarence M., SPE, Carnegie-Mellon U. Fort Jr., Tomlinson, Carnegie-Mellon U. Abstract Phase behavior studies were carried out for two systems containing pure surfactants but exhibiting behavior similar to that of commercial petroleum sulfonates. One system contained the isomerically pure surfactant sodium-8-phenyl-n-hexadecyl-n-sulfonate (Texas 1). The other contained sodium dodecyl sulfate (SDS). Additional components used in both systems were various pure short-chain alcohols, NaCl brine and n-decane. Aqueous solutions containing surfactant, cosurfactant, and NaCl were studied over a wide range of compositions with polarizing and modulation contrast microscopy, as well as the polarized light screening technique. Viscosity measurements were conducted on selected scans of the Texas 1 system. Maxima and minima of the scans were correlated with textural changes observed with microscopy. The aqueous solutions were contacted with equal volumes of n-decane, and phase behavior and interfacial tensions were determined. The middle microemulsion phase was found to be oil continuous close to the upper phase boundary and water continuous close to the lower phase boundary. Both the Texas 1 and SDS systems showed similar behavior in that the middle microemulsion phase was observed over the entire range of surfactant concentrations studied. Introduction Surfactant systems usually consisting of petroleum sulfonate, an alcohol, salt, and water have been used for enhanced oil recovery. Various parameters important to oil recovery by surfactant flooding, such as interfacial tension and viscosity, are related strongly to the phase behavior of the microemulsion systems. The relationship of ultralow interfacial tensions to phase separation has been treated in our laboratory. The recovery of petroleum from laboratory cores and field tests appears to be related directly to phase behavior. It is important to understand phase behavior to identify the mechanisms involved and improve the efficiency of the oil-recovery process. The physicochemical aspects of the phase behavior of microemulsion systems containing commercial petroleum sulfonates as surfactants have been well documented by Healy and Reed and others. However, the systems studied were not pure, and the commercial surfactants sometimes contained as much as 40% inactive ingredients. There is a need to develop model microemulsion systems using pure components. Such systems would provide an experimental platform for verifying or interpreting the implications of any model for the phase behavior of multicomponent microemulsion systems and also allow the behavior of commercial systems to be predicted and understood. The objective of our work has been to fulfill these needs. Microemulsions have been classified as lower phase (l), upper phase (u), or middle phase (m) in equilibrium with excess oil, excess brine, or both excess oil and brine, respectively. Transitions among these phases have been studied as functions of salinity, alcohol concentration, temperature, etc. The middle-phase microemulsion is particularly significant because microemulsion/excess brine and microemulsion/excess oil tensions can be ultra low simultaneously. The concept of an optimal parameter as proposed originally by Reed and Healy when equal amounts of oil and brine are solubilized in the middle phase has been followed in this paper. We have shown earlier that the structure of petroleum sulfonate solutions exhibits a general pattern of variation with salinity. SPEJ P. 53^

Sign in / Sign up

Export Citation Format

Share Document