Favorable Attributes of Alkaline-Surfactant-Polymer Flooding

SPE Journal ◽  
2008 ◽  
Vol 13 (01) ◽  
pp. 5-16 ◽  
Author(s):  
Shunhua Liu ◽  
Danhua Zhang ◽  
Wei Yan ◽  
Maura Puerto ◽  
George J. Hirasaki ◽  
...  
Keyword(s):  
Crude Oil ◽  
Phase Behavior ◽  
Anionic Surfactants ◽  
Naphthenic Acids ◽  
Mobility Control ◽  
Alkaline Solutions ◽  
Synthetic Surfactant ◽  
Optimal Salinity ◽  
Interfacial Tensions ◽  
Alkaline Surfactant Polymer

Summary A laboratory study of the alkaline-surfactant-polymer (ASP) process was conducted. It was found from phase-behavior studies that for a given synthetic surfactant and crude oil containing naphthenic acids, optimal salinity depends only on the ratio of the moles of soap formed from the acids to the moles of synthetic surfactant present. Adsorption of anionic surfactants on carbonate surfaces is reduced substantially by sodium carbonate, but not by sodium hydroxide. The magnitude of the reduction with sodium carbonate decreases with increasing salinity. Particular attention was given to a surfactant blend of a propoxylated sulfate having a slightly branched C16-17 hydrocarbon chain and an internal olefin sulfonate. In contrast to alkyl/aryl sulfonates previously considered for EOR, alkaline solutions of this blend containing neither alcohol nor oil were single-phase micellar solutions at all salinities up to approximately optimal salinity with representative oils. Phase behavior with a west Texas crude oil at ambient temperature in the absence of alcohol was unusual in that colloidal material, perhaps another microemulsion having a higher soap content, was dispersed in the lower-phase microemulsion. Low interfacial tensions existed with the excess oil phase only when this material was present in sufficient amount in the spinning-drop device. Some birefringence was observed near and above optimal conditions. While this phase behavior is somewhat different from the conventional Winsor phase sequence, overall solubilization of oil and brine for this system was high, leading to low interfacial tensions over a wide salinity range and to excellent oil recovery in both dolomite and silica sandpacks. The sandpack experiments were performed with surfactant concentrations as low as 0.2 wt% and at a salinity well below optimal for the injected surfactant. It was necessary that sufficient polymer be present to provide adequate mobility control, and that salinity be below the value at which phase separation occurred in the polymer/surfactant solution. A 1D simulator was developed to model the process. By calculating transport of soap formed from the crude oil and injected surfactant separately, it showed that injection below optimal salinity was successful because a gradient in local soap-to-surfactant ratio developed during the process. This gradient increases robustness of the process in a manner similar to that of a salinity gradient in a conventional surfactant process. Predictions of the simulator were in excellent agreement with the sandpack results. Background Although both injection of surfactants and injection of alkaline solutions to convert naturally occurring naphthenic acids in crude oils to soaps have long been suggested as methods to increase oil recovery, key concepts such as the need to achieve ultralow interfacial tensions and the means for doing so using microemulsions were not clarified until a period of intensive research between approximately 1960 and 1985 (Reed and Healy 1977; Miller and Qutubuddin 1987; Lake 1989). Most of the work during that period was directed toward developing micellar-polymer processes to recover residual oil from sandstone formations using anionic surfactants. However, Nelson et al. (1984) recognized that in most cases the soaps formed by injecting alkali would not be at the "optimal" conditions needed to achieve low tensions. They proposed that a relatively small amount of a suitable surfactant be injected with the alkali so that the surfactant/soap mixture would be optimal at reservoir conditions. With polymer added for mobility control, the process would be an alkaline-surfactant-polymer (ASP) flood. The use of alkali also reduces adsorption of anionic surfactants on sandstones because the high pH reverses the charge of the positively charged clay sites where adsorption occurs. The initial portion of a Shell field test, which did not use polymer, demonstated that residual oil could be displaced by an alkaline-surfactant process (Falls et al. 1994). Several ASP field projects have been conducted with some success in recent years in the US (Vargo et al. 2000; Wyatt et al. 2002). Pilot ASP tests in China have recovered more than 20% OOIP in some cases, but the process has not yet been applied there on a large scale (Chang et al. 2006).

Mechanistic Modeling of Alkaline/Surfactant/Polymer Floods

2009 ◽  
Vol 12 (04) ◽  
pp. 518-527 ◽  
Author(s):  
Hourshad Mohammadi ◽  
Mojdeh Delshad ◽  
Gary A. Pope
Keyword(s):  
Phase Behavior ◽  
Chemical Reactions ◽  
Oil Recovery ◽  
Numerical Models ◽  
Naphthenic Acids ◽  
Mechanistic Modeling ◽  
Synthetic Surfactant ◽  
Recovery Method ◽  
Optimum Salinity ◽  
Alkaline Surfactant Polymer

Summary Alkaline/surfactant/polymer (ASP) flooding is of increasing interest and importance because of high oil prices and the need to increase oil production. The benefits of combining alkali with surfactant are well established. The alkali has very important benefits such as lowering interfacial tension (IFT) and reducing adsorption of anionic surfactants that decrease costs and make ASP a very attractive enhanced-oil-recovery method, provided that the consumption is not too large and the alkali can be propagated at the same rate as the synthetic surfactant and polymer. However, the process is complex, so it is important that new candidates for ASP be selected taking into account the numerous chemical reactions that occur in the reservoir. The reaction of acid and alkali to generate soap and its subsequent effect on phase behavior is the most crucial for crude oils containing naphthenic acids. Mechanistic simulation of the ASP flood considering the chemical reactions, alkali consumption, and soap generation and the effect on the phase behavior is the key to success of future field operations. Using numerical models, the process can be designed and optimized to ensure the proper propagation of alkali and effective soap and surfactant concentrations to promote low IFT and a favorable salinity gradient. In this paper, we describe the ASP module of the UTCHEM simulator, which is the University of Texas chemical compositional simulator, with particular attention to phase behavior and the effect of soap on optimum salinity and solubilization ratio. Phase behavior data are presented for sodium carbonate and a blend of surfactants with an acidic crude oil that followed the conventional Winsor phase transition with significant three-phase regions even at low surfactant concentrations. The solubilization data at different oil concentrations were successfully modeled using Hand's rule. Optimum salinity and solubilization ratio were correlated with soap mole fractions using mixing rules. ASP coreflood results were successfully modeled taking into account the aqueous reactions, alkali/rock interactions, and phase behavior of soap and surfactant. Mechanistic simulations give insights into the propagation of alkali, soap, and surfactant in the core and aid in future coreflood and field-scale ASP designs.

A Modified HLD-NAC Equation of State To Predict Alkali/Surfactant/Oil/Brine Phase Behavior

SPE Journal ◽  
2018 ◽  
Vol 23 (02) ◽  
pp. 550-566 ◽  
Author(s):  
Soumyadeep Ghosh ◽  
Russell T. Johns
Keyword(s):  
Equation Of State ◽  
Phase Behavior ◽  
Oil Recovery ◽  
Naphthenic Acids ◽  
Phase Region ◽  
Measured Data ◽  
Synthetic Surfactant ◽  
Chemical Flooding ◽  
Mineral Surfaces ◽  
Dimensionless Equation

Summary Reservoir crudes often contain acidic components (primarily naphthenic acids), which undergo neutralization to form soaps in the presence of alkali. The generated soaps perform synergistically with injected synthetic surfactants to mobilize waterflood residual oil in what is termed alkali/surfactant/polymer (ASP) flooding. The two main advantages of using alkali in enhanced oil recovery (EOR) are to lower cost by injecting a lesser amount of expensive synthetic surfactant and to reduce adsorption of the surfactant on the mineral surfaces. The addition of alkali, however, complicates the measurement and prediction of the microemulsion phase behavior that forms with acidic crudes. For a robust chemical-flood design, a comprehensive understanding of the microemulsion phase behavior in such processes is critical. Chemical-flooding simulators currently use Hand's method to fit a limited amount of measured data, but that approach likely does not adequately predict the phase behavior outside the range of the measured data. In this paper, we present a novel and practical alternative. In this paper, we extend a dimensionless equation of state (EOS) (Ghosh and Johns 2016b) to model ASP phase behavior for potential use in reservoir simulators. We use an empirical equation to calculate the acid-distribution coefficient from the molecular structure of the soap. Key phase-behavior parameters such as optimum salinities and optimum solubilization ratios are calculated from soap-mole-fraction-weighted equations. The model is tuned to data from phase-behavior experiments with real crudes to demonstrate the procedure. We also examine the ability of the new model to predict fish plots and activity charts that show the evolution of the three-phase region. The predictions of the model are in good agreement with measured data.

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

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

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

Surfactant Phase Behavior and Retention in Porous Media

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

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

A Mechanistic Integrated Geochemical and Chemical-Flooding Tool for Alkaline/Surfactant/Polymer Floods

SPE Journal ◽  
2016 ◽  
Vol 21 (01) ◽  
pp. 32-54 ◽  
Author(s):  
Aboulghasem Kazemi Korrani ◽  
Kamy Sepehrnoori ◽  
Mojdeh Delshad
Keyword(s):  
Crude Oil ◽  
Phase Behavior ◽  
The United States ◽  
Mineral Dissolution ◽  
Mechanistic Modeling ◽  
United States Geological Survey ◽  
Chemical Flooding ◽  
Exchange Reactions ◽  
Asp Flooding ◽  
Alkaline Surfactant Polymer

Summary Mechanistic simulation of alkaline/surfactant/polymer (ASP) flooding considers chemical reactions between the alkali and the oil to form in-situ soap and reactions between the alkali and the minerals and brine. A comprehensive mechanistic modeling of such process remains a challenge, mainly caused by the complicated ASP phase behavior and the complexity of geochemical reactions that occur in the reservoir. Because of the lack of the microemulsion phase and/or lack of reactions that may lead to the consumption of alkali and resulting lag in the pH, a simplified ASP phase behavior is often used. A state-of-the-art geochemical package, IPhreeqc, of the United States Geological Survey was coupled with UTCHEM, an in-house research chemical-flooding reservoir simulator developed at The University of Texas at Austin (UT), for a robust, flexible, and accurate integrated tool to mechanistically model ASP floods. UTCHEM has a comprehensive three-phase (water, oil, microemulsion) flash package for the mixture of surfactant and soap as a function of salinity, temperature, and cosolvent concentration. Through this integrated tool, we are able to simulate homogeneous and heterogeneous (mineral dissolution/precipitation), irreversible, surface complexation, and ion exchange reactions under nonisothermal, nonisobaric, and both local-equilibrium and kinetic conditions. Italic words are defined in Appendix A. IPhreeqc has rich databases of chemical species and also the flexibility to include the alkaline reactions required for modeling ASP floods. Hence, to the best of our knowledge, for the first time, the important aspects of ASP flooding are considered. An algorithm is presented for modeling the geochemistry in an implicit-in-pressure-and-explicit-in-concentration solution algorithm. Finally, we show how to apply the integrated tool, UTCHEM-IPhreeqc, to match three different reaction-related chemical-flooding processes: ASP flooding in an acidic active crude oil, ASP flooding in a nonacidic crude oil, and alkaline/cosolvent/polymer flooding.

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^

Application of the Theory of Multicomponent, Multiphase Displacement to Three-Component, Two-Phase Surfactant Flooding

1981 ◽  
Vol 21 (02) ◽  
pp. 191-204 ◽  
Author(s):  
George J. Hirasaki
Keyword(s):  
Partition Coefficient ◽  
Phase Behavior ◽  
Oil Recovery ◽  
Chromatographic Separation ◽  
Partition Coefficients ◽  
Phase System ◽  
Surfactant Flooding ◽  
Two Phase ◽  
Optimal Salinity ◽  
Interfacial Tensions

Abstract The theory presented in a companion paper is illustrated for the case of three-component, two-phase (i.e., constant-salinity) surfactant flooding. The utility of this method is that, in addition to computation of specific cases, it provides a general qualitative understanding of the displacement behavior for different phase diagrams and different injection compositions. The phase behavior can be classified as to whether the partition coefficient is less than or greater than unity. The injection composition of the slug can be classified as to whether it is aqueous or oleic and whether it is inside or outside the region of tieline extensions.The theory provides an understanding of the displacement mechanisms for the three-component, two-phase system as a function of phase behavior and injection composition. This understanding aids the interpretation of phenomena such as the effects of dispersion, salinity gradient, chromatographic separation, and polymer/surfactant interaction. Introduction The phase behavior of surfactant with oil and brine is the underlying phenomenon of most surfactant-flood design philosophies. The surfactant slugs have been formulated either as (1) surfactant in water, (2) surfactant in oil, or (3) microemulsions containing both water and oil. Recovery of oil is thought to occur by solubilization, oil swelling, miscible displacement, and/or low interfacial tensions. The low interfacial tensions occur in a salinity environment such that three phases can coexist. At higher salinities the surfactant is in the oleic phase, and at lower salinities it is in the aqueous phase.Some recent investigators have preferred designing their process at a constant salinity even though their experiments indicated better oil recovery with a salinity contrast. Glover et al. point out that the optimal salinity is not constant in brines containing divalent ions and that phase trapping can result in large retention of surfactant in a system that was at optimal salinity at injected conditions. Nelson and Pope have demonstrated that good oil recovery is possible in systems containing formation brine with 120,000 ppm TDS and 3,000 ppm divalent cations if the drive salinity is sufficiently low such that the surfactant partitions into the aqueous phase. Moreover, the peak surfactant concentration in the effluent occurred in the three-phase environment where the lowest interfacial tension usually occurs.The purpose of this work is to understand better the mechanism of multiphase, multicomponent displacement so that the phase behavior can be used to advantage. The approach used is to examine in detail the displacement mechanism and behavior of a two-phase, three-component system. This understanding will build a foundation for examining more complex systems.Earlier, Larson and Hirasaki showed effects of oil swelling and the retardation of the surfactant front due to the surfactant partitioning into the oleic phase. Recently, Larson extended the work to finite slugs including oleic slugs. He showed the conditions necessary to have miscible or piston-like displacement. His work showed that systems with large partition coefficients are more tolerant to dispersive mixing. We show in this paper that his observation was probably the consequence of having a phase diagram with a constant partition coefficient. Todd et al. show the effect of the partition coefficients on the chromatographic separation and retention for a two-component surfactant system. Pope et al. evaluated the sensitivity of the performance of a surfactant flood to a number of factors. SPEJ P. 191^

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

Recent Advances in Surfactant EOR

SPE Journal ◽  
2011 ◽  
Vol 16 (04) ◽  
pp. 889-907 ◽  
Author(s):  
George J. Hirasaki ◽  
Clarence A. Miller ◽  
Maura Puerto
Keyword(s):  
Phase Separation ◽  
Crude Oil ◽  
Oil Recovery ◽  
Surfactant Solution ◽  
Naphthenic Acids ◽  
Mobility Control ◽  
Wettability Alteration ◽  
Recent Advances ◽  
Carbonate Formations

Summary In this paper, recent advances in surfactant enhanced oil recovery (EOR) are reviewed. The addition of alkali to surfactant flooding in the 1980s reduced the amount of surfactant required, and the process became known as alkaline/surfactant/polymer flooding (ASP). It was recently found that the adsorption of anionic surfactants on calcite and dolomite can also be significantly reduced with sodium carbonate as the alkali, thus making the process applicable for carbonate formations. The same chemicals are also capable of altering the wettability of carbonate formations from strongly oil-wet to preferentially water-wet. This wettability alteration in combination with ultralow interfacial tension (IFT) makes it possible to displace oil from preferentially oil-wet carbonate matrix to fractures by oil/water gravity drainage. The alkaline/surfactant process consists of injecting alkali and synthetic surfactant. The alkali generates soap in situ by reaction between the alkali and naphthenic acids in the crude oil. It was recently recognized that the local ratio of soap/surfactant determines the local optimal salinity for minimum IFT. Recognition of this dependence makes it possible to design a strategy to maximize oil recovery with the least amount of surfactant and to inject polymer with the surfactant without phase separation. An additional benefit of the presence of the soap component is that it generates an oil-rich colloidal dispersion that produces ultralow IFT over a much wider range of salinity than in its absence. It was once thought that a cosolvent such as alcohol was necessary to make a microemulsion without gel-like phases or a polymer-rich phase separating from the surfactant solution. An example of an alternative to the use of alcohol is to blend two dissimilar surfactants: a branched alkoxylated sulfate and a double-tailed, internal olefin sulfonate. The single-phase region with NaCl or CaCl2 is greater for the blend than for either surfactant alone. It is also possible to incorporate polymer into such aqueous surfactant solutions without phase separation under some conditions. The injected surfactant solution has underoptimum phase behavior with the crude oil. It becomes optimum only as it mixes with the in-situ-generated soap, which is generally more hydrophobic than the injected surfactant. However, some crude oils do not have a sufficiently high acid number for this approach to work. Foam can be used for mobility control by alternating slugs of gas with slugs of surfactant solution. Besides effective oil displacement in a homogeneous sandpack, it demonstrated greatly improved sweep in a layered sandpack.

Polymer/Surfactant Transport in Micellar Flooding

1981 ◽  
Vol 21 (05) ◽  
pp. 603-612 ◽  
Author(s):  
C.S. Chiou ◽  
G.E. Kellerhals
Keyword(s):  
Porous Media ◽  
Phase Separation ◽  
Crude Oil ◽  
Phase Behavior ◽  
Xanthan Gum ◽  
Water Soluble ◽  
Mobility Control ◽  
Rich Phase ◽  
Surfactant Systems ◽  
Polymer Transport

Abstract For the surfactant formulations used (particular surfactant concentration, surfactant type, cosolvent type, cosolvent concentration, etc.), the results show that surfactant systems containing polymer as a mobility control agent may exhibit adverse polymer transport behavior during flow through porous media. Polymer generally lagged behind the surfactant even though the two species were injected simultaneously in the surfactant slug. This poor polymer transport definitely could have a detrimental effect on the efficiency of a micellar flooding process in the field. Phase studies show that when some surfactant systems containing xanthan gum are mixed with crude oil at various salinities, a polymer-rich, gel-like phase forms. The polymer lag phenomenon in core tests can be related to phase separation due to divalent cations generated in situ as a result of ion exchange with the clays and the surfactant. Introduction and Background Proper design for mobility control is important in micellar or surfactant flooding to maintain stable displacement and prevent or reduce viscous fingering. Generally, effective mobility control is obtained by having the mobility of the polymer drive less than the mobility of the surfactant slug and the mobility of the surfactant slug less than the mobility of the oil/water bank. Oil-external and aqueous surfactant systems are designed to attain mobility control by two distinct approaches. In the oil-external case, increases in viscosity (compared with water) are largely a result of the presence of oil and the relatively high concentration of surfactant in the slug. The viscosity of aqueous surfactant systems frequently is increased by the addition of a polymer, usually either xanthan gum or polyacrylamide. There are drawbacks to both of these approaches. Use of a hydrocarbon such as crude oil (in the surfactant slug) to increase viscosity may result in injectivity problems due to wax and/or asphaltenes in the crude oil.Trushenski investigated the effects of sulfonate, cosurfacant, water, and salt concentrations on sulfonate/polymer incompatibility (multiple phases may form when polymer solution dilutes with a sulfonate containing micellar fluid). In dynamic core tests, this phase separation may result in one phase being trapped in the porous media. For the sulfonate/cosurfactant system (Mahogany AA and isopropyl alcohol) used, the results of static phase studies correlated with the incidence of phase trapping in dynamic core tests. Trushenski concluded that increasing the concentration of cosurfactant or cosolvent in the surfactant and polymer slugs could eliminate or reduce sulfonate/polymer incompatibility. In his dynamic core tests, the absolute brine permeability of the Berea cores was characteristically about 500 md. Polymer type (polyacrylamide or polysaccharide) did not appear to affect phase behavior appreciably. He identified sulfonate/polymer incompatibility as a previously unreported source of sulfonate loss. Trushenski also concluded that invasion of a surfactant slug by a water-soluble polymer can be eliminated or minimized if the surfactant slug contains low concentrations of crude oil.Pope et al. studied the phase behavior of surfactant/brine/alcohol systems both with and without polymer. Some of their various combinations also were equilibrated with a synthetic oil consisting of n-octane or an n-octane/benzene mixture. Both anionic and nonionic polymers were used. At a sufficiently high sodium chloride concentration, the oil-free (no added oil) mixtures showed phase separation into an aqueous polymer-rich phase and an aqueous surfactant-rich phase. They termed the salinity at which phase separation occurred the critical electrolyte concentration. SPEJ P. 603^

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