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 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^

Mixing Rules for Optimum Phase-Behavior Formulations of Surfactant/Oil/Water Systems

1979 ◽  
Vol 19 (05) ◽  
pp. 271-278 ◽  
Author(s):  
J.L. Salager ◽  
M. Bourrel ◽  
R.S. Schechter ◽  
W.H. Wade
Keyword(s):  
Phase Behavior ◽  
Oil Recovery ◽  
Practical Interest ◽  
Phase Region ◽  
Salinity Range ◽  
Mixing Rules ◽  
Recovery Efficiency ◽  
Middle Phase ◽  
Rich Phase ◽  
Three Phase

Abstract Many formulations used in surfactant flooding involve blends of surfactants designed to glue the best oil-recovery efficiency. Because oil-recovery efficiency usually is presumed to relate closely to surfactant/brine/oil phase behavior, it is of interest to understand the effect of mixing surfactants or of mixing oils on this phase behavior.We show that a correlation defining optimal behavior as a function of salinity, alcohol type and concentration, temperature, WOR (water/oil ratio), and oil type can be extended to mixtures of sulfonated surfactants and to those of sulfonates with sulfates and of sulfonates with alkanoates, provided the proper mixing rules are observed. provided the proper mixing rules are observed. The mixing rules apply to some mixtures of anionic and nonionic surfactants, but not to all. These mixtures exhibit some properties that may be of practical interest, such as increased salinity and practical interest, such as increased salinity and temperature tolerance. Introduction Recent studies have shown that formulation of the surfactant/brine/oil system is a key factor governing the performance of microemulsions designed to recover residual oil. These studies demonstrate that all optimal formulations exhibit characteristic properties that are remarkably similar. In general, properties that are remarkably similar. In general, the optimal microemulsion can solubilize large quantities of oil and connate water; in the presence of excess quantities of oil and water, a third surfactant-rich middle phase is formed. The interfacial tensions (IFT's) between the excess phases and the surfactant-rich phase are both low - about 10 dyne/cm (10 mN/m). Given an oil/brine system from a particular reservoir, one can achieve this formulation by varying the surfactant or the cosurfactant. Different oils, brines, or temperatures require formulations correspondingly altered to maintain optimal conditions. Previous studies have shown that the three-phase region exists over a range of values when one parameter, such as cosurfactant concentration, parameter, such as cosurfactant concentration, salinity, temperature, etc., is varied systematically (often called a scan). Thus, some ambiguity may exist with regard to the selection of those parameters representing the optimal formulation. Clearly, the optimum is that which recovers the most oil. However, tests are laborious, difficult to reproduce precisely, and sensitive to other factors, such as precisely, and sensitive to other factors, such as mobility, surfactant retention, wettability, etc. Therefore, it is desirable to impose an alternative definition that can be used for screening, though the final design still is dictated by core floods.Healy and Reeds have shown that the optimal formulation for oil recovery closely corresponds to that for which the IFT's between the excess oil and water phases and the surfactant-rich phase are equal. An almost equivalent criterion also was shown to be that point in the three-phase region for which the volume of oil solubilized into the middle phase equals the volume of brine. Furthermore, Salager et al. have used still another criterion that seems to be essentially equivalent to those used by Healy and Reed - an optimal salinity is defined as the midpoint of the salinity range for which the system exhibits three phases.These criteria are useful because they permit the screening of microemulsion systems using simple laboratory tests. SPEJ P. 271

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^

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

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 Topology of Phase Boundaries for Oil/Brine/Surfactant Systems and Its Relationship to Oil Recovery

1982 ◽  
Vol 22 (01) ◽  
pp. 28-36 ◽  
Author(s):  
M. Bourrel ◽  
C. Chambu ◽  
R.S. Schechter ◽  
W.H. Wade
Keyword(s):  
Phase Boundary ◽  
Phase Behavior ◽  
Phase Diagrams ◽  
Enhanced Oil Recovery ◽  
Oil Recovery ◽  
Single Phase ◽  
Phase Region ◽  
Alcohol Concentration ◽  
Phase Boundaries ◽  
Single Phase Region

Abstract Surfactant/oil/water phase diagrams have become the most important screening tool used to select microemulsion systems for enhanced oil recovery. The number of phases coexisting at a given salinity, the extent of the single-phase region, and the position of the phase boundaries all have relevance with respect to oil displacement efficiency. It is shown that the phase diagrams can be made to take on different configurations depending on the alcohol cosurfactant, the salinity, the impurities present in the surfactant, and the dispersity of the surfactant mixture. Besides the importance of the phase boundary shape, this study provides further insight into factors determining the height of the binodal surface on the pseudoternary phase diagram. Results show the effect of salinity as well as the surfactant, alcohol, and hydrocarbon types on the height of the binodal surface. It is shown that salinity is the main factor; other parameters have little or no influence once a surfactant has been selected. Finally the microemulsion viscosity is shown to be related to the proximity of the formulation to phase boundaries. Extensive data for one system are presented. Introduction It is now recognized that formulating surfactant/oil/brine systems that exhibit desirable phase behavior is an important step in optimizing performance of microemulsion systems for enhanced oil recovery. Oil is displaced by a combination of mechanisms-miscible displacement, swelling of the oil phase, and low tension displacement all of which are related to the topology of the phase boundaries in composition space. To predict the outcome of a particular project, a representation of the phase boundaries and their evolution when diluted with oil or brines having various proportions of divalent ions is required. For example, successful application of the salinity gradient concept demands phase relationships specially structured to accommodate the variations in salinity experienced by the surfactant slug during the course of the flood. Recent publications have dealt with the optimal salinity as a function of total amphiphile concentration (surfactant plus cosurfactant), and reported trends that are quite different from those found if the cosurfactant (alcohol) concentration is held constant. One purpose of this paper is to demonstrate that contorted phase boundaries found by Glover et al are caused by the variation of alcohol concentration when the concentration of total amphiphile is varied and because the direction that the phase boundaries twist or rotate is controlled by the nature of the alcohol. Another important factor is the extent of the single-phase region. More precisely, the height of the demixing curve in the pseudoternary representation should be minimized. This would permit, in principle, the amount of surfactant and cosurfactant in the micellar slug to be minimized. A correlation permitting the determination of the oil, salinity, alcohol, and surfactant at which the height of the demixing curve is minimized has been reported, but few data giving the value of the minimum height have been presented. This height is an important feature of the phase boundary topology and extensive measurements are reported here. The microemulsion viscosity must be high enough to help maintain mobility control. It is sometimes difficult to achieve the required levels of viscosity. Studies of microemulsion viscosity have been reported. We provide further data here and have related the microemulsion viscosities to phase behavior. Materials and Experimental Techniques The phase diagrams have been established by two techniques: a titration procedure and a grid-point technique. SPEJ P. 28^

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