Evaluation of the Salinity Gradient Concept in Surfactant Flooding

1983 ◽  
Vol 23 (03) ◽  
pp. 486-500 ◽  
Author(s):  
G.J. Hirasaki ◽  
H.R. van Domselaar ◽  
R.C. Nelson
Keyword(s):  
Active Region ◽  
Phase Behavior ◽  
Aqueous Phase ◽  
Surfactant Concentration ◽  
High Salinity ◽  
Salinity Gradient ◽  
Type Ii ◽  
Middle Phase ◽  
Optimal Salinity ◽  
Type Iii

Abstract Salinity design goals are to keep as much surfactant as possible in the active region and to minimize surfactant possible in the active region and to minimize surfactant retention. Achieving these is complicated becausecompositions change as a result of dispersion, chromatographic separation of components distributed among two or more phases, and retention by adsorption onto rock and/or absorption in a trapped phase-.in the presence of divalent ions, optimal salinity is not constant but a function of surfactant concentration and calcium/sodium ratio: andthe changing composition of a system strongly influences transport of the components. A one-dimensional (ID) six-component finite-difference simulator was used to compare a salinity gradient design with a constant salinity design. Numerical dispersion was used to evaluate the effects of dispersive mixing. These simulations show that, with a salinity gradient, change of phase behavior with salinity can be used to advantage both to keep surfactant in the active region and to minimize retention. By contrast, under some conditions with a constant salinity design. it is possible to have early surfactant breakthrough and/or large surfactant retention. Other experiments conducted showed that high salinity does retard surfactant, and, if the drive has high salinity. a great amount of surfactant retention can result. The design that produced the best recovery had the water flood brine over optimum and the drive under optimum; the peak surfactant concentration occurred in the active region and oil production ceased at the same point. Introduction The phase behavior of surfactant/oil/brine systems for different salinities is shown in Fig. 1. Low salinities. called "underoptimum" or "Type II(−)" phase behavior, are shown at the top of Fig. 1. In this kind of system, surfactant is partitioned predominantly into the aqueous phase. predominantly into the aqueous phase. High salinities, called "overoptimum" or "Type II(+)" phase behavior, are shown at the bottom of Fig. 1. In this kind of system, surfactant is partitioned predominantly into the oleic phase. When the oleic phase predominantly into the oleic phase. When the oleic phase has a low oil concentration, the oil is said to be "swollen" by the surfactant and brine. At moderate salinities, the system can have up to three phases and is called "Type III." This is illustrated in the phases and is called "Type III." This is illustrated in the middle of Fig. 1. The salinity at which the middle phase has a WOR of unity is called "optimal salinity" because the lowest interfacial tensions (IFT's) usually occur near this salinity. As salinity increases, there is a steady progression from Type II(−) to Type III to Type II(+) phase behavior. The middle-phase composition moves from the brine side of the diagram to the oil side. The two-phase regions that correspond to the Type II(−) and Type II( +) systems can be seen above the three-phase region in Fig. 1.

The Salinity-Requirement Diagram - A Useful Tool in Chemical Flooding Research and Development

1982 ◽  
Vol 22 (02) ◽  
pp. 259-270 ◽  
Author(s):  
Richard C. Nelson
Keyword(s):  
Phase Equilibrium ◽  
Surfactant Concentration ◽  
Salinity Gradient ◽  
Reservoir Rock ◽  
Chemical Flooding ◽  
Optimal Salinity ◽  
Type Iii ◽  
Oil Displacement ◽  
Small Pore ◽  
Micro Emulsion

Abstract Optimal salinity, the level of brine salinity at which a chemical flooding surfactant displaces oil most efficiently, is related to midpoint salinity and to the range of salinity over which the phase environment is Type III. These three conditions are functions of surfactant concentration-usually decreasing as surfactant concentration decreases, particularly if the brine contains multivalent cations. A salinity-requirement diagram, constructed from phase equilibrium data, expresses quantitatively the dependency of midpoint salinity and the Type III range on surfactant concentration. Because surfactant concentration decreases as a flood with a small-pore-volume chemical slug proceeds, a salinity-requirement diagram can provide insight into the performance of chemical floods. Examples are presented that support the proposal that chemical flooding is most efficient when conducted in a salinity gradient. A phenomenon in which a "wedge" of oil is left on the bottom of the core by a chemical flood is related to the salinity-requirement diagram for the system, and the effect of ion exchange on such diagrams is discussed. Introduction In the nest paper of this series, we concluded that chemical flooding under normal reservoir flow rates can be treated as an equilibrium process. Results of laboratory chemical floods, some of which were reported in that paper, indicate that the phases that form when oil, surfactant, and brine are mixed and allowed to equilibrate in sample tubes also form in the pores of reservoir rock during a chemical flood. Consequently, a reservoir under chemical flood can be visualized as a series of connected mixing cells, with phase equilibrium attained in each cell. Mathematical simulators of the chemical flooding process based on this physical model have been published, and a general theory of multicomponent, multiphase displacement in porous media has been described and illustrated. We defined in that first paper three types of phase environment: Types II(-), II(+), and III. We concluded from our experiments that one objective in designing chemical flooding, systems should be to keep as much of the surfactant as possible in the Type III phase environment, near midpoint salinity, for as long as possible during, the course of the flood. In the second paper of the series, we emphasized that the salinity requirement of a chemical flooding system usually changes during a chemical flood as adsorption and dispersion cause the surfactant concentration to decrease. The salinity requirement is the salinity required for the surfactant/brine/oil system to be at midpoint salinity (i.e., that point in the Type III phase environment where the concentration of oil equals the concentration of brine in the microemulsion, middle phase). Healy and Reed and others have observed that optimal salinity for oil displacement is at or near midpoint salinity. We use midpoint salinity rather than optimal salinity in our work because midpoint salinity is defined precisely. We assume that the sum of the micro emulsion/excess oil and micro emulsion/excess brine interfacial tensions is minimal and oil displacement efficiency is maximal near midpoint salinity. Our experimental results are consistent with this assumption. For most anionic surfactants. midpoint salinity decreases as surfactant concentration decreases, particularly in the presence of multivalent cations. The dependency on surfactant concentration of midpoint salinity and of the range of salinity over which the system is Type III is depicted on a salinity requirement diagram. Such diagrams are similar to those presented by Glover et al. The utility of salinity-requirement diagrams was illustrated in Ref. 9 by considering the results of four laboratory chemical floods that differed only in the salinity of their polymer drives. SPEJ P. 259^

Interpretation of the Change in Optimal Salinity With Overall Surfactant Concentration

1982 ◽  
Vol 22 (06) ◽  
pp. 971-982 ◽  
Author(s):  
George J. Hirasaki
Keyword(s):  
Sodium Chloride ◽  
Phase Behavior ◽  
Surfactant Concentration ◽  
Equilibrium Composition ◽  
Chemical Flooding ◽  
Alkyl Ether ◽  
Divalent Ions ◽  
Optimal Salinity ◽  
Phase Rule ◽  
Compositional Simulator

Abstract Background. For chemical flooding formulations, optimal salinity changes with overall surfactant concentration when the phase behavior is observed in test tubes. Applying these observations to the mathematical simulator is questionable because chromatographic mechanisms during displacement through porous media result in different compositions. Purpose. This work sought the mechanism for the observed change so that calculated optimal salinity can be expressed through the appropriate intensive variable rather than overall surfactant concentration. Method. Association of the alcohol has been described by partition coefficients for distribution of the alcohol among brine, oil, and surfactant. The alcohol was isopropanol (IPA), 1-butanol (NBA), or tertiary amyl alcohol (TAA) in the systems in which they were included and was used to represent a disulfonate in the system with Petrostep petroleum sulfonate. Association of sodium and divalent ions with surfactant has been described by the Donnan equilibrium model, which experimental observations show can be applied to microemulsions as well as to micelles. Conclusions. For the seven systems investigated, the change in optimal salinity is a function of (1) the alcohol associated with the surfactant and (2) the divalent ion fraction of the associated counterions. Introduction Reed and Healy reviewed the concept of optimal salinity for minimum inter-facial tension (IFT) and its relationship to phase behavior. They showed that, as a first approximation, phase behavior can be represented by electrolyte concentration and three pseudocomponents: brine, oil, and surfactant plus cosolvent. If the system actually contains three components plus sodium chloride, optimal salinity should be independent of overall surfactant concentration and WOR. However. in the system Reed and Healy investigated, optimal salinity changed with overall surfactant concentration and WOR, which indicates that the system did not contain just sodium chloride plus three additional components. To handle this problem, Vinatieri and Fleming suggested using regression analysis to determine the best set of pseudocomponents. Then alcohol can be included with the oil and brine as pseudocomponents. Blevins et al. examined the phase behavior of a quaternary system (with brine as a pseudocomponent) by examining pseudoternary planes on a quaternary diagram. Glover et al. showed that the change in optimal salinity of a system containing divalent ions can be modeled by (1) considering the equilibrium composition of the brine, and (2) describing optimal salinity as a linear function of the concentration of divalent ions associated with the sulfonate. They assumed that NEODOL 25-3S did not associate divalent ions. (NEODOL 25-3S is a sodium salt of C12-C15 alkyl ether sulfate, with an average ethylene oxide number of three. Hereafter in this paper it is abbreviated as N253S.) Pope and Nelson showed that phase behavior and IFT's can be modeled in a compositional simulator when optimal salinity and the upper and lower limits of the Type III environment are known. The purpose of this work is to model alcohol or multiple surfactant components and divalent ions so that they can be included in a compositional simulator. Thermodynamic Analysis The Gibbs phase rule is used to show that a four-component system of pure oil, surfactant, water, and NaCl has an optimal salinity that does not depend on overall surfactant concentration. SPEJ P. 971^

A Three-Parameter Representation of Surfactant/Oil/Brine Interaction

1983 ◽  
Vol 23 (04) ◽  
pp. 669-682 ◽  
Author(s):  
Maura C. Puerto ◽  
Ronald L. Reed
Keyword(s):  
Crude Oil ◽  
Phase Behavior ◽  
Molar Volume ◽  
Surfactant Concentration ◽  
Low Pressure ◽  
Precise Description ◽  
Optimal Salinity ◽  
Parameter Representation ◽  
Reservoir Conditions ◽  
Oil Mixtures

Abstract When optimal salinity, C, and solubilization parameter Vo/Vs are augmented by Oil molar volume, V mo, the resulting three-parameter representation provides a more precise description of microemulsion phase behavior precise description of microemulsion phase behavior than has previously been available. It then becomes possible to introduce the idea of equivalent oils (Ego's) possible to introduce the idea of equivalent oils (Ego's) as a replacement for the equivalent alkane carbon number (EACN), which is shown to lack some of the properties needed to implement efficient preliminary properties needed to implement efficient preliminary screening of microemulsions for EOR. Broadly speaking, oils are "equivalent" when-they have the same molar volumes, optimal salinities, and solubilization parameters. If, in addition to equivalence, oils are required to have equal viscosities and similar phase behavior as a function of surfactant concentration, phase behavior as a function of surfactant concentration, then it may be possible to replace microemulsion floods of live crude at high pressure with floods of appropriately diluted dead crude at low pressure. This paper places EACN in perspective by means of the three-parameter representation, explores parallel effects of temperature and alcohol cosolvents, and reveals essential nonlinearities in optimal salinity as a function of oil composition (and hence molar volume) for mixtures of various oils. Much of this is subsequently used to develop methods for preparation of Ego's and the more complex but evidently essential equivalent systems (EqS's) needed to model live crudes. Introduction An essential step in design of a microemulsion flood is to test the proposed system and optimize it by using reservoir conditions. fluids, and rock. However, especially when pressure and temperature are high and there is gas in solution, this can be very complex and time consuming, so that it is preferable to minimize this aspect of the total design procedure. Under reservoir conditions, surfactant system phase behavior is also difficult to accomplish and assess in a satisfactory way. In fact, an opaque crude sometimes causes discrimination of the various kinds of phases and emulsions to be problematical. Therefore, it has long been a goal to replace live crude with a pure oil or mixture of pure oils. If this could be accomplished, then phase behavior and the bulk of screening floods could be done at reservoir temperature, but under low pressure, considerably easing the design process. It should be stressed, however, that laboratory tests conducted under the most realistic conditions still are required in final phases of design work. During the attempt to formulate a live-crude replacement algorithm, it became evident that the existing description of surfactant/oil/brine phase behavior was not unique. For example, a single surfactant at fixed temperature can exhibit different interfacial tensions (IFT's) for certain nonhomologous pure oils and yet all tensions can correspond to the same optimal salinity. Or a collection of oils can be found that all furnish the same middle-phase solubilization parameters but have different optimal salinities. Hence, a parameter is needed that characterizes the oil in addition to optimal salinity and solubilization parameters. In this paper, oil molar volume is proposed as one such additional parameter, and the extent to which this improves the characterization of phase behavior is discussed. The resulting three-parameter correlation then is used to replace dead or live crude with pure oil and/or pure-oil/crude-oil mixtures that are equivalent in a pure-oil/crude-oil mixtures that are equivalent in a certain sense related to phase behavior and flooding performance. performance. SPEJ p. 669

Surfactant Phase Behavior and Retention in Porous Media

1979 ◽  
Vol 19 (03) ◽  
pp. 183-193 ◽  
Author(s):  
C.J. Glover ◽  
M.C. Puerto ◽  
J.M. Maerker ◽  
E.L. Sandvik
Keyword(s):  
Porous Media ◽  
Phase Behavior ◽  
Surfactant Concentration ◽  
Divalent Cations ◽  
Reservoir Rock ◽  
Residual Oil ◽  
Optimal Salinity ◽  
Interfacial Tensions ◽  
Production Research ◽  
Surfactant Systems

Glover, C.J.,* SPE-AIME, Exxon Production Research Puerto, M.C., SPE-AIME, Puerto, M.C., SPE-AIME, Exxon Production Research Co. Maerker, J.M., SPE-AIME, Exxon Production Research Co. Sandvik, E.L., SPE-AIME, Exxon Production Research Co. Abstract Surfactant retention in reservoir rock is a major factor limiting effectiveness of oil recovery using microemulsion flooding processes. Effects of salinity and surfactant concentration on microemulsion phase behavior have a significant impact on relative phase behavior have a significant impact on relative magnitudes of retention attributed to adsorption vs entrapment of immiscible microemulsion phases.Surfactant retention levels were determined by effluent sample analyses from microemulsion flow tests in Berea cores. Data for single surfactant systems containing NaCl only and multicomponent surfactant systems containing monovalent and divalent cations are included. Retention is shown to increase linearly with salinity at low salt concentrations and depart from linearity with higher retentions above a critical salinity. This departure from linearity is shown to correlate with formation of upper-phase microemulsions. The linear trend, therefore, is attributed to surfactant adsorption, and retention levels in excess of this trend are attributed to phase trapping.Divalent cations are shown to influence microemulsion phase behavior strongly through formation of divalent-cation sulfonate species. A useful method for predicting phase behavior in systems containing divalent cations is described. This method combines equilibrium expressions with a relationship defining the contribution of each surfactant component to optimal salinity. Observed experimental data are compared with predicted data. Introduction Two essential criteria that must be met for successful recovery of residual oil by chemical flooding arevery low interfacial tensions between the chemical bank and residual oil and between the chemical bank and drive fluid andsmall surfactant retention losses to reservoir rock. If retention is excessive, interfacial tensions eventually will become high enough to retrap residual oil in the remainder of the reservoir.Previous studies have described several mechanisms responsible for surfactant retention in porous media. These include adsorption, porous media. These include adsorption, precipitation, partitioning into a residual oil phase, precipitation, partitioning into a residual oil phase, and entrapment of immiscible microemulsion phases. Of particular interest is Trushenski's discussion of microemulsion phase trapping as a consequence of surfactant-polymer interaction, and a supporting statement that similar behavior often was observed when microemulsions were diluted with polymer-free brine. Here, we attempt to provide some understanding of this surfactant dilution phenomenon by examining phase behavior as a function of salinity, divalent-ion content, and surfactant concentration. Experimental Procedures Surfactant Systems Two surfactant systems were used in this study. (Specific microemulsion compositions are discussed later.) One system was the 63:37 volumetric mixture of the monoethanol amine salt of dodecylorthoxylene sulfonic acid and tertiary amyl alcohol (MEAC12OXS/TAA) described by Healy et al. The oil component for these microemulsions was a mixture of 90% Isopar M TM and 10% Heavy Aromatic Naptha.(TM)** The brine contained NaCl only. SPEJ P. 183

Homologous Bursts of Spectral Type II

1969 ◽  
Vol 1 (5) ◽  
pp. 185-186 ◽  
Author(s):  
R. T. Stewart ◽  
B. Hardwick
Keyword(s):  
Active Region ◽  
Spectral Type ◽  
Single Frequency ◽  
Radio Bursts ◽  
Type Ii ◽  
Type Iii ◽  
Dynamic Spectra

In 1961 Fokker and Roosen suggested that the concept of homology as applied to solar optical flares by Ellison, McKenna and Reid could be extended to flare-associated radio events as well, since successive flares within the same centre of activity sometimes produce radio bursts which look remarkably similar on single-frequency records. Teresa Fortini reported very similar ionospheric responses due to X-radiation from flares recurring in the same active region. In 1950 Wild noted similarities in the dynamic spectra of type III bursts occurring within periods of minutes.

Equilibrium of a Microemulsion That Coexists With Oil or Brine

1983 ◽  
Vol 23 (05) ◽  
pp. 829-847 ◽  
Author(s):  
Chun Huh
Keyword(s):  
Phase Behavior ◽  
Chain Length ◽  
Phase State ◽  
Water Soluble ◽  
The Other ◽  
Ionic Surfactants ◽  
Middle Phase ◽  
Lower Phase ◽  
Optimal Salinity ◽  
Drop Radius

Huh, Chun; SPE; Exxon Production Research Co. Abstract When salinity, or an equivalent variable, is increased, microemulsions generally undergo orderly transitions from a lower-to middle- to upper-phase. Even though the significance of such multiphase behavior has been well recognized in the design of surfactant flood processes, their quantitative nature in terms of the molecular structures of the surfactant lipophile, hydrophile, and the oil and brine salinity has not been fully understood. A theory of lower- and upper-phase microemulsions that gives reasonable predictions of their interfacial tensions (IFT's) and phase behavior is presented. In the theory, the surfactant monomers adsorbed at oil/brine interface cause the interface to bend as a result of an imbalance between the hydrophile/brine interaction on the one hand and lipophile/oil interaction on the other. With sufficient imbalance, high local curvature causes small drops of one phase to disperse into the other. In addition, interactions between these drops are taken into account for the microemulsion equilibrium. The theory also offers a possibility of being able to describe the hydrophile/lipophile-balanced state (optimal salinity state of Healy and Reed) in terms of the tendency of surfactant layer at the oil/brine interface to bend. Introduction Understanding the phase behavior of microemulsions is an important step in designing surfactant flooding processes and interpreting the results when they are applied to recover tertiary oil. It is well established that the phase behavior of many microemulsion systems, even those containing a large phase behavior of many microemulsion systems, even those containing a large number of different components can be represented qualitatively using pseudoternary diagrams similar to those in Fig. 1. Fig. 1a shows the pseudoternary diagrams similar to those in Fig. 1. Fig. 1a shows the lower-phase microemulsion in equilibrium with excess oil, Figs. 1b and 1c the middle-phase microemulsion in equilibrium with both oil and brine, and Fig. 1d the upper-phase microemulsion coexistent with excess water. Even though not all microemulsions conform to this simple picture, it serves as a good approximation frequently enough to use it as a basis for discussing microemulsion phase behavior. Transitions such as those shown by Fig. 1 can be produced by changing any of a large number of variables in a systematic manner. The phase shifts from "a" to "d" generally occur with increases in the salinity of the brine, the alkyl chain length of the surfactant, the aromaticity of the oil, the addition of a highly oil- soluble alcohol and a temperature increase (for non-ionic surfactants). The shifts also occur with decreases in the chain length of oil, the number of hydrophilic groups (e.g., ethylene oxide) of the surfactant, the addition of a highly water-soluble alcohol, and a temperature decrease (for most ionic surfactants). Since microemulsion phase transitions will be determined by the manner in which microemulsion structure depends on changes in the variables described above, many experimental studies have been made to determine microemulsion structure. Ultracentrifuge and light-scattering measurements show that the lower-phase microemulsion consists of spherical oil drops with radius of about 50 to 1,000 k in water. As it moves toward the middle-phase state (see Figs. 1a and 1b), the drop radius grows. On the other hand, the upper-phase microemulsion consists of small water drops in oil, and as it moves toward the middle-phase state (Figs. 1c and 1d), the drop radius again grows. Very little is known about the structure of middle-phase microemulsions. SPEJ p. 829

scholarly journals Effect of Baggase NaLS Surfactant Concentration to Increase Recovery Factor

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Arinda Ristawati ◽  
Sugiatmo Kasmungin ◽  
Rini Setiati
Keyword(s):  
Phase Behavior ◽  
Oil Recovery ◽  
Surfactant Concentration ◽  
Recovery Factor ◽  
Test Results ◽  
Surfactant Flooding ◽  
Middle Phase ◽  
Basic Substance ◽  
Surfactant Phase ◽  
Behavior Test

<p class="NoSpacing1"><em>Surfactant flooding may increase oil recovery by lowering interfacial tension between oil and water. Bagasse is one of the organic materials which contain fairly high lignin, where lignin is the basic substance of making Natrium Lignosulfonate (NaLS) Surfactant. In this research, bagasse based surfactant was applied for surfactant flooding. The research was divided into two sections, namely: phase behavior test and NaLS Surfactant flooding where the water contained 70,000 ppm NaCl. Two surfactant concentrations which were used were 0.75% and 1.5% NaLS surfactant. Phase behavior tests were carried out to find the middle phase emulsion formation. Based on phase behavior test results, the percentage of emulsion volume for 0.75% and 1.5% NaLS is 13.75% and 8.75%, respectively. NaLS surfactant flooding was performed for to obtain the best recovery factor. FTIR equipment used determine recovery factor. The optimum condition was obtained at 0.75% NaLS surfactant concentration where the recovery factor was 4.4%.</em><em></em></p>

Criteria for Structuring Surfactants To Maximize Solubilization of Oil and Water: Part 1-Commercial Nonionics

1982 ◽  
Vol 22 (05) ◽  
pp. 743-749 ◽  
Author(s):  
Alain Graciaa ◽  
Lester N. Fortney ◽  
Robert S. Schechter ◽  
William H. Wade ◽  
Seang Yiv
Keyword(s):  
Phase Behavior ◽  
Oil Recovery ◽  
Nonionic Surfactants ◽  
Phase Region ◽  
Microemulsion System ◽  
Middle Phase ◽  
Optimal Salinity ◽  
Surfactant System ◽  
Hydrophilic Lipophilic Balance ◽  
Surfactant Systems

Abstract The phase behavior of nonionic surfactants having the same hydrophilic/lipophilic balance (HLB) but differing molecular weights has been studied. It is shown that the optimal alkane carbon number (ACN) depends on the HLB, but that increasing the hydrophobe molecular weight narrows the middle phase region, increases the solubilization parameter, and decreases the interfacial tension (IFT). We found that the width of the three-phase region is in simple inverse proportion to the solubilization parameter at optimal salinity and that the multiple of IFT times the square of the solubilization is a constant. We also found it possible to synthesize nonionics that rival anionics in the properties mentioned above. Introduction There is increasing evidence that the phase behavior of surfactant/oil/brine systems and the efficiency of oil recovery with micellar solutions are connected intimately. For instance, laboratory core floods have shown that surfactant systems exhibit maximum oil recovery at the optimal salinity. The concept of optimal salinity, introduced by Healy and Reed, is especially useful because it pen-nits screening of surfactant systems by relatively simple experiments requiring the observation of the number and the types of phases that coexist at equilibrium when surfactant/oil/brine mixtures are blended. Optimal salinity, defined as that middle-phase microemulsion system containing equal volumes of oil and water, is not difficult to determine, and, thus, conditions for the most efficient surfactant system can be established. It is now well known that many different surfactant systems have the same optimal salinity. Further, it generally has been assumed, but not definitely established by laboratory experiments that the preferred surfactant system, selected from a group of systems having the same optimal salinity, will be that which solubilizes the largest volume of oil and brine per unit mass of surfactant. We do not necessarily subscribe to this simple view. since there are many factors other than solubilization (such as surfactatant retention) that may influence oil recovery efficiency however, all other factors being equal, it is reasonable to attempt to maximize solubilization, especially because it has been found synonymous with minimal IFT's-an equally important factor governing effectiveness of oil recovery. This paper seeks to identify some surfactant structural features that will lead to increased solubilization and decreased IFT. We have addressed this important question in past publications but have met with only limited success. The difficulty has been that changing the surfactant structure dictates that a second corresponding change be made so that the resulting system would remain optimal. For instance, one can increase the length of the hydrocarbon tail of the surfactant molecule and at the same time compensate for this change either by decreasing the amount of hydrophobic alcohol added to the system or by decreasing the salinity of the system. The results obtained in this manner have remained difficult to interpret because all changes can and most often do alter the solubilization of oil and water in the middle-phase microemulsion. Therefore, it was not possible to separate that pan of the resulting solubilization change caused strictly by the modification of the surfactant structure. In the study discussed here, we made compensating changes in the surfactant structure, keeping all other variables fixed. For nonionic surfactants, compensating changes can be made in several ways. SPEJ P. 743^

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^

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