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^

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^

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

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

Multiphase Microemulsion Systems

1976 ◽  
Vol 16 (03) ◽  
pp. 147-160 ◽  
Author(s):  
R.N. Healy ◽  
R.L. Reed ◽  
D.G. Stenmark
Keyword(s):  
Interfacial Tension ◽  
Physicochemical Properties ◽  
Phase Behavior ◽  
Oil Recovery ◽  
Displacement Efficiency ◽  
Oil Composition ◽  
Alkyl Aryl ◽  
Optimal Salinity ◽  
Interfacial Tensions ◽  
Multiphase Behavior

Abstract Economical microemulsion flooding inevitably involves microemulsion phases immiscible with oil or water, or both; oil recovery is largely affected by displacement efficiency during the immiscible regime. Therefore, it is essential to understand the role of interfacial tension in relation to multiphase microemulsion behavior. Three basic types of multiphase systems are identified and used to label phase transitions that occur when changes are made in salinity, temperature, oil composition, surfactant structure, cosolvent, and dissolved solids in the aqueous phase. Directional effects of these changes on phase behavior, interfacial tension, and solubilization parameter are tabulated for the alkyl aryl sufonates studied. A relationship between interfacial tension and phase behavior is established. This provides the phase behavior is established. This provides the basis for a convenient method for preliminary screening of surfactants for oil recovery. Interfacial tensions were found to correlate with the solubilization parameter for the various microemulsion phases, a result that can substantially reduce the number of interfacial tensions that must be determined experimentally for a given application. Introduction A previous paper established that microemulsion flooding is a locally miscible process until slug breakdown and is an immiscible, rate-dependent displacement thereafter; furthermore, for an effective flood, most of the oil recovered is acquired during the immiscible regime. An extensive study of single-phase regions defined classes of micellar structures for a particular surfactant; however, it was subsequently shown these did not affect oil recovery, provided viscous, lamellar structures were avoided. Optimal salinity was introduced as defining a ternary diagram having the least extensive multiphase region, a desirable feature in that locally miscible displacement is prolonged. Immiscible displacement after slug breakdown is known to depend on interfacial tension through its inclusion in the capillary number. A brief study showed chat interfacial tension varied widely throughout the multiphase region; accordingly, it is anticipated that oil recovery will depend on details of multiphase behavior in relation to interfacial tension, as well as on injection composition. Consider a flood sufficiently advanced that the microemulsion slug has broken down. A microemulsion phase remains that is immiscible with water or oil, phase remains that is immiscible with water or oil, or both, and displacement has assumed an immiscible character. The problem is twofold: to design a microemulsion slug that effectively displaces oil at the front and that is effectively displaced by water at the back. Both aspects are essential and, therefore, both microemulsion-oil and microemulsion-water interfacial tensions must be very low. The condition where these two tensions are low and equal will be of particular significance. The purpose of this paper is to explore physicochemical properties of multiphase physicochemical properties of multiphase microemulsion systems with a view toward understanding immiscible aspects of microemulsion flooding, and with the expectation of developing systematic screening procedures useful for design of optimal floods. Equilibration is an essential part of this study. Even the simplest of these systems is so complex it may well happen that nonequilibrium effects will never be understood sufficiently to be usefully accommodated in mathematical simulation of microemulsion flooding. In any event, equilibration, although time consuming, leads to a coherent picture of multiphase behavior that can be correlated with flooding results. Multiphase behavior of "simple" ternary systems divides into three basic classes. Dependence of phase behavior on salinity, with respect to these phase behavior on salinity, with respect to these classes, leads to correlations of interfacial tension with the solubilization parameter. These correlations are studied in relation to surfactant structure, temperature, cosolvents, oil composition, and brine composition. Optimal salinity again plays an important role, especially in relation to interfacial tension. SPEJ P. 147

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^

Mixture of Different Surfactants Enhanced Chemical Flooding for Suijing Oil Recovery

2014 ◽  
Vol 1004-1005 ◽  
pp. 688-691
Author(s):  
Lu Ming Jiang ◽  
Qing Zhe Jiang ◽  
Zhao Zheng Song ◽  
Xiao Xiao
Keyword(s):  
Interfacial Tension ◽  
Crude Oil ◽  
Oil Recovery ◽  
Surfactant Solution ◽  
Ionic Surfactant ◽  
Chemical Flooding ◽  
Mixed Surfactant ◽  
Alkylbenzene Sulfonate ◽  
Anion Surfactant ◽  
Test Result

We investigate six different surfactants in interfacial tension (IFT) between the surfactant solution and the crude oil from Suijng oilfield. Based on the measurement of interfacial tension, the anion surfactant Heavy alkylbenzene sulfonate (HABS) and non-ionic surfactant alkyl glycoside (APG) are selected for the formulation of mixed surfactant. The IFT between the mixed surfactant solution comprising the HABS and APG and crude oil from Suijing can be reduced to ultralow.The experimental results indicate that the selected mixed surfactant formulation (0.20%HABS+0.10%APG) has a good performance on the tolerance of temperature and salinity and the coreflood test result indicate that the effective of the formulation was high which led to significant oil recovery (56.48%TOR).

A Study of Oil Displacement by Microemulsion Systems Mechanisms and Phase Behavior

1980 ◽  
Vol 20 (06) ◽  
pp. 459-472 ◽  
Author(s):  
G.P. Willhite ◽  
D.W. Green ◽  
D.M. Okoye ◽  
M.D. Looney
Keyword(s):  
Interfacial Tension ◽  
Phase Behavior ◽  
Oil Recovery ◽  
Surfactant Solution ◽  
Residual Oil ◽  
Surfactant Flooding ◽  
Displacement Efficiency ◽  
High Concentration ◽  
The Core ◽  
Oil Displacement

Abstract Microemulsions located in a narrow single-phase region on the phase diagram for the quaternary system consisting of nonane, isopropyl alcohol, Witco TRS 10-80 petroleum sulfonate, and brine were used to investigate the effect of phase behavior on displacement efficiency of the micellar flooding process. Microemulsion floods were conducted at reservoir rates in 4-ft (1.22-m) Berea cores containing brine and residual nonane. Two floods were made using large (1.0-PV) slugs. A third flood used a 0.1-PV slug followed by a mobility buffer of polyacrylamide. Extensive analyses of the core effluents were made for water, nonane, alcohol, and mono- and polysulfonates. An oil bank developed which broke through at 0.08 to 0.1 PV, and 48 to 700/0 of the oil was recovered in this bank which preceeded breakthrough of monosulfonate and alcohol. Coincidental with the arrival of these components of the slug, the effluent became a milky white macroemulsion which partially separated upon standing. Additional oil was recovered with the macroemulsion. Ultimate recoveries were 90 to 100% of the residual oil. Low apparent interfacial tension was observed between the emulsion and nonane. Alcohol arrived in the effluent at the same time as monosulfonate even though there was extensive adsorption of the sulfonate. Further, alcohol appeared in the effluent well after sulfonate production had ceased, indicating retention of the alcohol in the core. A qualitative model describing the displacement process was inferred from the appearance of the produced fluids and the analyses of the effluents. Introduction Surfactant flooding (micellar or microemulsion) is one of the enhanced oil recovery methods being developed to recover residual oil left after waterflooding. Two approaches to surfactant flooding have evolved in practice. In one, relatively large volumes (0.25 PV) of low-concentration surfactant solution are used to create low-tension waterfloods.1,2 Oil is mobilized by reduction of interfacial tension to levels on the order of about 10−3 dyne/ cm (10−3 mN/m). The second approach involves the application of small volumes (0.03 to 0.1 PV) of high-concentration solutions.3,4 These solutions are miscible to some extent with the formation water and/or crude oil. Consequently, miscibility between the surfactant solution and oil and/or low interfacial tensions contribute to the oil displacement efficiency. The relative importance of these mechanisms has been the subject of several papers5,6 and discussions.7,8

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

Observations on the Coalescence Behavior of Oil Droplets and Emulsion Stability in Enhanced Oil Recovery

1978 ◽  
Vol 18 (06) ◽  
pp. 409-417 ◽  
Author(s):  
D.T. Wasan ◽  
S.M. Shah ◽  
N. Aderangi ◽  
M.S. Chan ◽  
J.J. McNamara
Keyword(s):  
Interfacial Tension ◽  
Crude Oil ◽  
Oil Recovery ◽  
Emulsion Stability ◽  
Surfactant Solution ◽  
Chemical Additives ◽  
Oil In Water ◽  
Tertiary Oil Recovery ◽  
Oil Water ◽  
Low Tension

Original manuscript received in Society of Petroleum Engineers office Sept. 20, 1977. Paper accepted for publication June 2, 1978. Revised manuscript received Aug. 2, 1978. Paper (SPE 6846) was presented at SPE-AIME 52nd Annual Fall Technical Conference and Exhibition, held in Denver, Oct. 9-12, 1977. Abstract Results of experiments on the coalescence of crude oil drops at an oil-water interface and interdroplet coalescence in crude oil-water emulsions containing petroleum sulfonates and cosurfactant as surfactant systems with other chemical additives were analyzed in terms of interracial viscosity, interfacial tension, interfacial charge, and thickness of the films surrounding the microdroplets. A qualitative correlation was found between coalescence rates and interfacial viscosities; however, there appears to be no direct correlation with interfacial tension. New insight has been gained into the influence of emulsion stability in tertiary oil recovery by surfactant/polymer flooding in laboratory core tests. We concluded that those systems that result in relatively stable emulsions yield poor coalescence rates and, hence, poor oil recovery, Introduction The ability of the surfactant/polymer system to initiate and to propagate an oil bank is the single most important feature of a successful tertiary oil-recovery process. The mechanisms of oil-bank formation and development are yet unknown. It has been suggested that without the initiation of the oil bank, the process behaves more like the unstable injection of a surfactant solution alone, where the oil is produced by entrainment or emulsification in the flowing surfactant stream. In a laboratory study of the initial displacement of residual hydrocarbons by aqueous surfactant solutions, Childress and Schechter and Wade observed that those systems that spontaneously emulsified and coalesced rapidly yielded better oil recovery than those systems that spontaneously formed stable emulsions. Recently, Strange and Talash, Whitley and Ware, and Widmeyer et al. reported results of Salem (IL) low-tension, water-flood tests that used Witco TRS 10-80 TM petroleum sulfonate surfactant solution. They found stable oil-in-water emulsions at the observer well in addition to emulsion problems at the production well and reported that problems at the production well and reported that actual oil recovery was about one-quarter the target value. These studies clearly suggested that poor efficiency of oil recovery results from emulsion stability problems in the low-tension surfactant or micellar processes. Vinatieri presented results of experiments on the stability of crude-oil-in-water emulsions that coo be produced during a surfactant or micellar flood. More recently, we have assessed the rigidity of interfacial films and its relationship to coalescence rate through measurements of interfacial viscosities of crude oils contacted against aqueous solutions containing various concentrations of surfactants and other pertinent chemical additives. Our data clearly indicate that in the absence of a commercial surfactant, interfacial viscosity builds up rapidly, coalescence is inhibited, and the resulting emulsion is quite stable. These phenomena also have been observed by Gladden and Neustadter. Several studies were conducted on the structure of film-forming material at the crude oil/water interface, its effect on emulsion stability, and the role of such films in oil recovery by water or caustic solution displacements. Rigid films were found to reduce the amount of oil recovered. Our studies also have shown that the addition of a commercial surfactant lowered both the interfacial viscosity (ISV) and interfacial tension (IFT) of the crude oil-aqueous solution system. However, the concentration at which both the IFT and ISV are minimized cannot be identified by measuring IFT alone. We have conducted a cinephotomicrographic examination of spontaneous emulsification and a microvisual study of the displacement of residual crude oil by aqueous surfactant solutions in micromodel porous media. SPEJ P. 409

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