Interfacial Tension and Phase Behavior of Surfactant Systems

1978 ◽  
Vol 18 (04) ◽  
pp. 242-252 ◽  
Author(s):  
W.H. Wade ◽  
James C. Morgan ◽  
R.S. Schechter ◽  
J.K. Jacobson ◽  
J.L. Salager
Keyword(s):  
Molecular Weight ◽  
Interfacial Tension ◽  
Crude Oil ◽  
Phase Behavior ◽  
Oil Recovery ◽  
Surfactant Concentration ◽  
Low Molecular Weight ◽  
Middle Phase ◽  
Surfactant Systems ◽  
Low Tension

Abstract The conditions necessary for optimum low tension and phase behavior at high surfactant concentrations are compared with those required at low surfactant concentrations, where solubilization effects are not usually visible. Major differences in tension behavior between the high and low concentration systems may be observed when the surfactant used contains a broad spectrum of molecular species, or if a higher molecular weight alcohol is present, but not otherwise in the systems studied. We compared the effects of a number of aliphatic alcohols on tension with phase behavior. An explanation of these results, and also of other observed parameter dependences, is proposed in terms of changes in surfactant chemical potential. Surfactant partitioning data is presented that supports this concept. Introduction Taber and Melrose and Brandner established that tertiary oil recovery by an immiscible flooding process should be possible at low capillary process should be possible at low capillary numbers. In practice, the required capillary number, which is a measure of the ratio of viscous to capillary forces governing displacement of trapped oil, may be achieved by lowering the oil/water interfacial tension to about 10(-3) dyne/cm, or less. Subsequent research has identified a number of surfactants that give tensions of this order with crude oils and hydrocarbon equivalents. Interfacial tension studies tended to fall into two groups. Work at low surfactant concentrations, typically 0.7 to 2 g/L, has established that a crude oil may be assigned an equivalent alkane carbon number. Using pure alkanes instead of crude oil has helped the study of system parameters affecting low tension behavior. Important parameters examined include surfactant molecular structure, and electrolyte concentration, surfactant concentration, surfactant molecular weight, and temperature. At higher surfactant concentrations, interfacial tension has been linked to the phase behavior of equilibrated systems. When an aqueous phase containing surfactant (typically 30 g/L), electrolyte, and low molecular weight alcohol is equilibrated with a hydrocarbon, the surfactant may partition largely into the oil phase, into the aqueous phase, or it may be included in a third (middle) phase containing both water and hydrocarbon. Low interfacial tensions occur when the solubilization of the surfactant-free phase (or phases) into the surfactant-containing phase is maximized. Maximum solubilization and minimum tensions have been shown to be associated with the formation of a middle phase. Both the high and low surfactant concentration studies have practical importance because even though a chemical flood starts at high concentration, degradation of the injected surfactant slug will move the system toward lower concentrations. This study investigates the relationship between tension minima found with low concentration systems, and low tensions found with equivalent systems at higher surfactants concentrations, particularly those in which third-phase formation occurs. Many of the systems studied here contain a low molecular weight alcohol, as do most surfactant systems described in the literature or proposed for actual oil recovery. Alcohol originally was added to surfactant systems to help surfactant solubility, but can affect tensions obtained with alkanes, and with refined oil. Few systematic studies of the influence of alcohol on tension behavior exist. Puerto and Gale noted that increasing the alcohol Puerto and Gale noted that increasing the alcohol molecular weight decreases the optimum salinity for maximum solubilization and lowest tensions. The same conclusions were reached by Hsieh and Shah, who also noted that branched alcohols had higher optimum salinities than straight-chain alcohols of the same molecular weight. Jones and Dreher reported equivalent solubilization results with various straight- and branched-chain alcohols. In this study, we fix the salinity of each system and instead vary the molecule; weight of the hydrocarbon phase. SPEJ P. 242

Optimum Formulation of Surfactant/Water/Oil Systems for Minimum Interfacial Tension or Phase Behavior

1979 ◽  
Vol 19 (02) ◽  
pp. 107-115 ◽  
Author(s):  
J.L. Salager ◽  
J.C. Morgan ◽  
R.S. Schechter ◽  
W.H. Wade ◽  
E. Vasquez
Keyword(s):  
Molecular Weight ◽  
Phase Behavior ◽  
Oil Recovery ◽  
Middle Phase ◽  
Interfacial Tensions ◽  
Three Phase ◽  
Optimum Formulation ◽  
The Subject ◽  
Tension State ◽  
Low Tension

Abstract A screening test used to help select surfactant systems potentially effective for oil recovery is to identify those formulations that yield middle-phase microemulsions when mixed with sufficient quantities of oil and brine. A correlation is presented to link these variables regarding their presented to link these variables regarding their contributions to middle-phase formation: structure of the sulfonated surfactant, alkane carbon number (ACN), and alcohol type and concentration. WOR and temperature effects are introduced as correction terms added to the empirical correlation.Sets of variables that give middle-phase microemulsions are shown as identical to those defining the low tension state without observable middle phases. This generally occurs for low surfactant phases. This generally occurs for low surfactant concentrations. Introduction Healy and Reed and Healy et al. have shown that the phase behavior of surfactant/brine/oil systems is a key factor in interpreting the performance of oil recovery by microemulsion performance of oil recovery by microemulsion processes. By systematically varying salinity, processes. By systematically varying salinity, they found low interfacial tensions and high solubilization of both oil and water in the microemulsion phase to occur in or near the salinity ranges giving phase to occur in or near the salinity ranges giving three phases. Since both low interfacial tensions and a high degree of solubilization are considered desirable for oil recovery, the conditions for three-phase formation assume added importance. Similar conclusions have been reported in other recent papers.Several investigators have considered the effect of different variables on the range of salinities for which three phases form. This optimum salinity (a more precise definition is given in a subsequent section) has been found to decrease with increasing surfactant molecular weight, and to increase with increasing chain length of the alcohol cosurfactant. Studies on the effect of alcohols by Jones and Dreher and Salter provided results similar to those reported by Hsieh and Shah.The interfacial tension at surfactant concentrations low enough so that a discernible third phase does not form has been the subject of considerable phase does not form has been the subject of considerable investigation regarding surfactant molecular weight and structure, oil ACN, salinity and surfactant concentration, and alcohol addition. A recent paper was a first attempt to tie together the low paper was a first attempt to tie together the low tension state observed at low surfactant concentrations and the three-phase region observed at higher surfactant concentrations. All indications point to an inextricable intertwining of phase point to an inextricable intertwining of phase behavior, surfactant partitioning, solubilization, and low tensions. This paper corroborates the equivalence of three-phase behavior and minimum tension as criteria for optimum formulation and presents a correlation that quantifies the trends presents a correlation that quantifies the trends observed previously. EXPERIMENTAL Aqueous phases containing surfactant, electrolyte (NaCl), and alcohol were contacted with an oil phase by shaking and allowed to stand until phase phase by shaking and allowed to stand until phase volumes became time independent for 2 days. All concentrations are expressed in grams of chemical per cubic centimeter of aqueous phase (g/cm3) per cubic centimeter of aqueous phase (g/cm3) before contacting with the hydrocarbon phase. Unless otherwise noted, the oil phase represents 20% of the initial total volume. All measurements, unless otherwise noted, were conducted at room temperature (25 plus or minus 1 degrees C). SPEJ p. 107

Low Interfacial Tensions Involving Mixtures of Surfactants

1977 ◽  
Vol 17 (02) ◽  
pp. 122-128 ◽  
Author(s):  
W.H. Wade ◽  
J.C. Morgan ◽  
J.K. Jacobson ◽  
R.S. Schechter
Keyword(s):  
Interfacial Tension ◽  
Crude Oil ◽  
Surfactant Concentration ◽  
Electrolyte Concentration ◽  
Hydrocarbon Mixture ◽  
Surfactant Mixtures ◽  
Interfacial Tensions ◽  
System Variables ◽  
Low Tension ◽  
Scaling Rule

Abstract The interfacial tension of surfactant mixtures with hydrocarbons obeys a simple scaling rule. Many apparently inert surfactants give low tensions when in mixtures; the scaling rule still applies to these mixtures. The influence of surfactant structure and molecular weight on low-tension behavior is examined, and the application of these results to the optimization of surfactant flooding systems is discussed. Introduction It has been shown that the interfacial-tension behavior of a given crude oil with a surfactant solution of the sulfonate type may be modeled by replacing the crude oil with one particular alkane. The number of carbon atoms in the alkane is referred to as the equivalent alkane carbon number (EACN) of the crude oil, and this EACN is independent of the surfactant used (at fixed standard conditions). This equivalency of a crude oil and an alkane is a result of the simple averaging behavior of hydrocarbons when mixed. Any hydrocarbon may be assigned an EACN value. For instance, when homologous series of alkyl benzenes and alkanes are run against the petroleum sulfonate TRS 10-80 at 2 gm/liter of surfactant with 10 gm/liter NaCl present, heptyl benzene and heptane, respectively, give minimum interfacial tensions, a. The EACN of heptyl benzene is 7, since it is equivalent to heptane. A simple averaging rule will give the EACN of a hydrocarbon mixture : (1) where x is the mole fraction of the ith component. Thus, an equimolar mixture of undecane (EACN 11) and heptyl benzene (EACN 7) has an EACN of 9. If a surfactant gives a low (minimum) sigma against nonane (EACN 9), it will also give a low sigma against the above mixture. Eq. 1 implies that a crude oil, which is a multicomponent hydrocarbon mixture, may be assigned an EACN. This has been verified experimentally. For example, Big Muddy field crude oil has an EACN of 8.5. Therefore, any surfactant phase giving a minimum tension against an equimolar mixture of octane and nonane gives a low tension against Big Muddy crude. All crude oils rested to date have EACN's ranging from 6 to 9. For a given surfactant, the alkane of minimum tension (min) may be affected by the electrolyte concentration or type, the temperature, the surfactant concentration, or the presence of a cosurfactant. These system variables may be adjusted until the nmin for a surfactant matches exactly the EACN of a crude oil. For any particular surfactant, many different combinations of variables will give the same n min value; therefore, there are many possible systems, each with n = EACN, available for crude oil recovery. In practice, however, the system variables may be manipulated to a limited extent only. The temperature of an oil field is fixed, and the surfactant concentration is limited by considerations of solubility and expense. The electrolyte concentration and type is partly determined by oilfield conditions and is limited by the effect on surfactant solubility. These limitations mean that many of the surfactants presently available on a large enough scale for use in low-tension flooding will not give minimum tensions in the range required (n of 6 to 9). This paper shows how minimal sigma's in the required range may be found for some of these "off-scale" surfactants when they are used in surfactant mixtures. The hypothesis tested here is that surfactant mixtures average in a manner analogous to the averaging of hydrocarbons in the oil phase. It will be shown that each surfactant component may be assigned an n value and that the alkane of minimum tension of a mixture of surfactants, (n), is then given by (2) where x is now the mole fraction of the ith component of the surfactant mixture. This greatly extends the number of surfactants that may be considered as candidates for use in low interfacial-tension flooding. SPEJ P. 122

Competing Roles of Interfacial Tension and Surfactant Equivalent Weight in the Development of a Chemical Flood

1982 ◽  
Vol 22 (04) ◽  
pp. 472-480 ◽  
Author(s):  
S.L. Enedy ◽  
S.M. Farouq Ali ◽  
C.D. Stahl
Keyword(s):  
Interfacial Tension ◽  
Crude Oil ◽  
Oil Recovery ◽  
Salt Concentration ◽  
Surfactant Concentration ◽  
Evolutionary Process ◽  
Chemical Flooding ◽  
Equivalent Weight ◽  
Residual Oil ◽  
Tertiary Oil Recovery

Abstract This investigation focused on developing an efficient chemical flooding process by use of dilute surfactant/polymer slugs. The competing roles of interfacial tension (IFT) and equivalent weight (EW) of the surfactant used, as well as the effect of different types of preflushes on tertiary oil recovery, were studied. Volume of residual oil recovered per gram of surfactant used was examined as a function of these variables and slug size. Tertiary oil recovery increased with an increase in the dilute surfactant slug size and buffer viscosity. However, low IFT does not ensure high oil recovery. An increase in surfactant EW used actually can lead to a decrease in oil recovery. Tertiary oil recovery was also sensitive to preflush type. Reasons for the observed behavior are examined in relation to the surfactant properties as well as to adsorption and retention. Introduction Two approaches are being used in development of surfactant /polymer-type chemical floods:a small-PV slug of high surfactant concentration, ora large-PV slug of low surfactant concentration. This study deals with the latter-i.e., dilute aqueous slugs (with polymer added in many cases) containing less than or equal 2.0 wt% sulfonates and about 0. 1 wt% crude oil. Because the dilute slug contains little of the dispersed phase, an aqueous surfactant slug usually is unable to displace the oil miscibly; however, residual brine is miscible with the slug if the inorganic salt concentration is not excessive. The dilute, aqueous petroleum sulfonate slug lowers the oil/water IFT. overcoming capillary forces. This process commonly is referred to as locally immiscible oil displacement. Objectives The objective of this work was to develop an efficient dilute surfactant/polymer slug for the Bradford crude with a variety of sulfonate combinations. Effects of varying the slug characteristics such as equivalent weight, IFT, salt concentration, etc. on tertiary oil recovery were examined. Materials and Experimental Details The petroleum sulfonates and the dilute slugs used in this study are listed in Tables 1 and 2, respectively. The crude oil tested was Bradford crude 144 degrees API (0.003 g/cm3), 4 cp (0.004 Pa.s)]. The polymer solutions were prefiltered and driven by brines of various concentrations (0.02, 1.0, and 2.0% NACl). In many cases, the polymer was added to the slug. Conventional coreflood equipment described in Ref. 3 was used. Berea sandstone cores (unfired) 2 in, (5 cm) in diameter and 4 ft (1.3 m) in length were used for all tests, with a new core for each test. Porosity ranged from 19.3 to 21.0%, permeability averaged 203 md, and the waterflood residual oil saturation averaged 33.1%. IFT's were measured by the spinning drop method. Viscosities were measured with a Brookfield viscosimeter and are reported here for 6 rpm (0.1 rev/s). The dilute slugs containing polymer exhibited non-Newtonian behavior. Without polymer the behavior was Newtonian. Sulfonate concentration in the oleic phase was determined by an infrared spectrophotometer, while the concentration in the aqueous phase was measured by ultraviolet (UV) absorbance analysis. Discussion of Results Slug development in this investigation was an evolutionary process. Dilute slugs were developed and core tested in a sequential manner (Table 2). Slugs 100 through 200 yielded insignificant ternary oil recoveries (largely because of excessive adsorption and retention), but the results helped determine improvements in slug compositions and in the overall chemical flood. This paper gives results for the more efficient slugs only. SPEJ P. 472^

Phase Behavior and Properties of a Petroleum Sulfonate Blend

1981 ◽  
Vol 21 (05) ◽  
pp. 573-580 ◽  
Author(s):  
J.H. Bae ◽  
C.B. Petrick
Keyword(s):  
Interfacial Tension ◽  
Crude Oil ◽  
Phase Behavior ◽  
Oil Recovery ◽  
Surfactant Solution ◽  
Phase Region ◽  
Salinity Range ◽  
Equal Weight ◽  
Optimal Salinity ◽  
Petroleum Sulfonate

Abstract A sulfonate system composed of Stepan Petrostep TM 465, Petrostep 420, and 1-pentanol was investigated. The system was found to give ultralow interfacial tension against crude oil in a reasonable range of salinity and sulfonate concentrations. It also was found that sulfonate partitioned predominantly into the microemulsion phase. However, a significant amount also partitioned into water and, at high salinity, into the oil phase. On the other hand, the oil-soluble 1-pentanol partitioned mostly into oil and microemulsion phases.The interfacial tension between excess oil and water phases was ultralow, in the range of 10-3 mN/m. The tensions were close to and paralleled those between the middle and water phases. The trend remained the same even when the alcohol content changed. This means that in the salinity range that produces a three-phase region, below the optimal salinity, the water phase effectively displaces both oil and middle phases, even though the oil may not be displaced effectively by the middle phase. The implication is that, from an interfacial tension point of view, the oil recovery would be more favorable in the salinity range below the optimal salinity with the mixed petroleum sulfonate system used here. This was confirmed by oil recovery tests in Berea cores. It also was concluded that the change in viscosity upon microemulsion formation might have a significant influence on the surfactant flood performance. Introduction During a surfactant flood, the injected slug of surfactant solution undergoes complex changes as it traverses the reservoir. The surfactant solution is diluted by mixing with reservoir oil and brine and by depletion of surfactant due to retention. Also, the reservoir salinity rarely is the same as that of the injected solution. Moreover, there is chromatographic separation of sulfonate and cosurfactant.When phase equilibrium between oil, brine, and injected surfactant is reached in the front portion of the slug, a microemulsion phase is formed. This phase behavior and its importance in oil recovery have been the subject of numerous papers in recent years. The microemulsion phase formed in the reservoir contacts fresh reservoir brine and oil and undergoes further changes. All these changes are accompanied by property changes of the phases that affect oil recovery.The objective of this paper is to investigate the properties of a blend of commercial petroleum sulfonates and its behavior in different environments. The phase volume behavior and changes in the properties of different phases and their effects on oil recovery were studied. This work was done as part of the design of a surfactant process for a field application. Therefore, a crude oil was used as the hydrocarbon phase. Experimental Procedures A blend of Petrostep 465 and 420 from Stepan Chemical Co. was used as the surfactant. An equal weight of each sulfonate on a 100% active basis was mixed. 1-pentanol from Union Carbide Corp. was used as a cosurfactant. Unless otherwise stated, a 50g/kg sulfonate concentration was used in the solution. We used symbols to denote the formulation. The first number in the symbol indicates the 1-pentanol concentration; the last number indicates the NaCl concentration. Thus, 15 P 10 means that the solution consists of 50 g/kg sulfonate, 15 g/kg 1-pentanol, and 10 g/kg NaCl. The sulfonate blend first was mixed with alcohol, and then the required amount of NaCl brine was added to make the solution. SPEJ P. 573^

Use of Perspective Plots To Aid in Determining Factors Affecting Interfacial Tensions Between Surfactant Solutions and Crude Oil

1982 ◽  
Vol 22 (03) ◽  
pp. 350-352
Author(s):  
G.E. Kellerhals
Keyword(s):  
Crude Oil ◽  
Aqueous Phase ◽  
Oil Recovery ◽  
Surfactant Concentration ◽  
Reservoir Rock ◽  
Surfactant Flooding ◽  
Rich Phase ◽  
Interfacial Tensions ◽  
Surfactant Systems ◽  
The Impact

Abstract In surfactant flooding, low interfacial tensions (IFT's) are required for recovery of additional significant quantities of crude oil from a reservoir rock. This paper indicates the usefulness of perspective plots to facilitate comparison of sets of IFT data. Such perspective plots simplify the process of screening various surfactant systems for enhanced oil recovery. Introduction Numerous articles have been written about the effects and/or importance of IFT between oil and aqueous phases in determining ultimate oil recovery during a phases in determining ultimate oil recovery during a secondary (waterflooding) or tertiary oil-recovery process. In the area of micellar/polymer or surfactant process. In the area of micellar/polymer or surfactant flooding, IFT has been studied extensively both by industrial and by academic investigators. A simplistic summary of this work is that low IFT's (generally corresponding to high capillary numbers ( are required for recovery of additional significant quantities of crude oil from a reservoir rock. Method Development Several variables influence between an oil-rich phase and a surfactant-containing aqueous phase. During phase and a surfactant-containing aqueous phase. During a surfactant flood, variations in surfactant concentration and salt concentration will occur as a result of mixing of the chemical slug with the pre flush (or formation brine) and polymer drive (" rear mixing" ). Nelson investigated salt concentrations required during a chemical flood to achieve efficient oil displacement. Since these variables (and others) change during the progress of a flood, it is desirable to determine the impact of these changes on the IFT between the oil- and water-rich phases. To assess the importance of changes in these two key variables (surfactant concentration and salinity) on IFT, an x-y plot may be constructed with values of each variable along the axes. The IFT for a particular surfactant concentration and salinity then is obtained experimentally and the numerical value placed at the corresponding (x, y) point on the plot. The resultant figure/table can be referred to as an IFT map. Points of equal, or about equal, IFT can be connected to produce an IFT contour map. In the investigation of the effect(s) of temperature on a given surfactant system and crude oil, IFT maps might be constructed for each of the pertinent temperatures. IFT's might be determined at six different sodium chloride concentrations (e.g., 1.0, 1.5, 2.0, 3.0, 4.0, and 5.0 wt%) and four surfactant concentrations (e.g., 0.085, 0.064, 0.042, and 0.021 meq/mL), resulting in IFT maps (for each temperature) each consisting of 24 IFT values. A comparison of the values of one map to the values of a second map (measurements made at different temperature) then is required to determine the impact of the temperature change. A single value for IFT for a given salinity and surfactant concentration assumes that the system is two-phase, because two IFT's can be measured for a three-phase system consisting of an oil-rich phase, a water-rich phase, and a microemulsion phase. phase. A method to allow easier comparison for the relatively large number of IFT data points that may be obtained during the study/screening of various surfactant systems at various conditions is described in this paper. The technique consists of interpolating between IFT values and then plotting the data with a perspective plotting routine. The method allows comparisons of IFT values for different crude oils, temperatures, cosolvent types, surfactant types, hardness ion concentrations, etc., through visual scanning of a perspective plot ranter than through trying to judge or compare numerical IFT values of an IFT map. SPEJ p. 350

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^

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^

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