Correlation of Emulsion Stability With Phase Behavior in Surfactant Systems for Tertiary Oil Recovery

1980 ◽  
Vol 20 (05) ◽  
pp. 402-406 ◽  
Author(s):  
James E. Vinatieri
Keyword(s):  
Phase Behavior ◽  
Oil Recovery ◽  
Emulsion Stability ◽  
Equilibrium Phase ◽  
Phillips Petroleum ◽  
The North ◽  
Three Phase ◽  
Tertiary Oil Recovery ◽  
Surfactant Systems ◽  
Oilfield Operations

Abstract This paper describes a study of the emulsions which could occur during a pilot surfactant flood, such as that conducted by Phillips Petroleum Co. in the North Burbank Unit, Osage County, OK. The phase behavior of this surfactant system can be characterized by three types of microemulsions, with the transition from one type to another being a function of the salinity. The rate at which emulsions coalesce was seen to correlate directly with the type of microemulsion. Coalescence was slow for macroemulsions at low salinities, rapid at intermediate salinities (where the final state was a three-phase system), and varied from slow to rapid at salinities above the three-phase region. Knowledge of the correlation between phase behavior and emulsion stability can be useful in treating macroemulsions produced during a surfactant flood. Introduction With the increased emphasis currently being placed on the use of surfactants for tertiary oil recovery, a potential problem exists with emulsions which can be produced as a consequence of a surfactant flood. For example, if a channeling problem between an injection well and a production well should occur, it may be possible to produce relatively large amounts of surfactant at moderately high concentrations (0.2 to 2.0070). Under these conditions, emulsions of oil and brine could be stabilized by the presence of the surfactant and could pose a serious problem. Although these emulsions are thermodynamically unstable and ultimately should separate into bulk oil and water phases, the presence of surfactants can increase greatly the time required for such separations. Typical oilfield operations allow, at most, several hours for this separation of phases to occur, but some emulsions containing surfactants may require weeks or even months to separate. Thus, a definite need exists for being able to accelerate this coalescence process. Phillips Petroleum Co. is conducting a pilot surfactant flood in the North Burbank Unit (NBU) in Osage County.1,2 The work reported here was directed at developing a contingency plan for breaking emulsions which may be produced by this surfactant flood. The problem of studying emulsions produced by a surfactant flood has two aspects:the nature of the phases which result when thermodynamic equilibrium finally is attained andthe rate at which this equilibrium state is reached. This is not to imply that any emulsion can be described completely by characterization of these two properties but rather that these are the two properties most important to oilfield operations and, hence, form the basis for the work reported here. The next section discusses the equilibrium properties of surfactant systems and the one following discusses the coalescence of emulsions. The fourth section describes the use of chemical demulsifiers to accelerate coalescence. Equilibrium Phase Behavior The equilibrium phase behavior of systems of oil and water containing appreciable amounts of surfactant (i.e., 0.5%) is characterized by the presence of microemulsions.1,3-5 These microemulsion phases have a high degree of structure and may contain large amounts of both oil and water.

Multivariate Optimization of Surfactant Systems for Tertiary Oil Recovery

1981 ◽  
Vol 21 (01) ◽  
pp. 77-88 ◽  
Author(s):  
James E. Vinatieri ◽  
Paul D. Fleming
Keyword(s):  
Oil Recovery ◽  
Degrees Of Freedom ◽  
Multivariate Optimization ◽  
Phase Rule ◽  
Two Degrees Of Freedom ◽  
Number Of Components ◽  
Petroleum Sulfonate ◽  
Three Phase ◽  
Tertiary Oil Recovery ◽  
Surfactant Systems

Abstract A new method of optimization has been developed for tertiary oil recovery systems employing surfactants. This method simultaneously adjusts all composition variables in a manner which greatly reduces the total number of compositions which need to be investigated experimentally. This multivariate optimization technique has been applied to two petroleum sulfonate systems, one containing a pure hydrocarbon and the other containing a crude oil. In both cases, significant reductions of interfacial tensions were achieved relative to those obtained by conventional optimization with respect to salinity alone. Surfactant systems for tertiary oil recovery commonly involve at least five components: oil, water, surfactant, cosurfactant, and electrolyte. The optimization of such systems is hindered by this large number of components and because interpolation of behavior is often difficult. Previously, such systems have been optimized by adjusting concentrations of individual components empirically. These empirical optimizations have indicated that surfactant systems which form three phases are preferred for oil recovery although they are not necessarily fully optimized. As stated by the Gibbs phase rule, a five-component, three-phase system has only two degrees of freedom at constant temperature and pressure. These two degrees of freedom can be identified mathematically by making use of chemical analysis of a three-phase sample. Thus, optimization of three-phase surfactant systems can be accomplished by adjusting only two variables, resulting in a dramatic reduction of time and effort required to optimize such systems. For the systems studied, both the volume per unit mass of surfactant and the viscosity of the microemulsion phase are increased significantly even though the optimization was based on interfacial tension only. These bonuses should lead to improved sweep efficiency in the displacement process. Introduction Surfactant systems have received much attention recently as a means for increasing the recovery of oil from a subterranean reservoir.1–5 Typically, these systems employ a petroleum sulfonate as the surfactant and an alcohol as a cosurfactant or co solvent. Thus, when the oil and brine (water plus electrolyte) also are considered, these oil recovery systems are seen to contain at least five components. Because of the high cost of surfactant systems, it is important that any such system be optimized to provide the greatest oil recovery at the lowest cost. Unfortunately, this optimization is hindered by, at least, these three factors:the large number of components and the correspondingly large number of possible compositions which must be evaluated,interactions between components which make interpolation of behavior difficult, andthe relative difficulty of performing displacement tests in porous media.

The Use of Pseudocomponents in the Representation of Phase Behavior of Surfactant Systems

1979 ◽  
Vol 19 (05) ◽  
pp. 289-300 ◽  
Author(s):  
J.E. Vinatieri ◽  
P.D. Fleming
Keyword(s):  
Phase Diagram ◽  
Phase Behavior ◽  
Oil Recovery ◽  
Dimensional Space ◽  
Multicomponent Systems ◽  
Tertiary Oil Recovery ◽  
Oil Water ◽  
Surfactant Systems ◽  
Lower Dimensional ◽  
Water Alcohol

Abstract A new method is developed to represent the phase behavior of multicomponent systems. This method uses fewer pseudocomponents than true components, but unlike conventional methods in which pseudocomponents are often chosen arbitrarily, the pseudocomponents are often chosen arbitrarily, the method uses regression analysis to find a "best" set of pseudocomponents.The method is applied to two surfactant systems of the type used for tertiary oil recovery. One system contains a crude oil (from the North Burbank Unit, Osage County, OK) and the other contains a pure hydrocarbon, 1-phenyltetradecane. For both systems the representation in terms of the pseudocomponents chosen by the regression analysis is significantly more faithful than that obtained by conventional methods.Since the considerations discussed here are general, they should be applicable to a wide range of phase studies in multicomponent systems. For example, they should be illuminating when applied to oil recovery by gas injection (carbon dioxide, natural gas, etc.), and to extraction processes, as well as to surfactant systems. Introduction Systems containing surface active agents have attracted a great deal of attention in connection with tertiary oil recovery. In many of these systems optimum oil recovery has been found to be strongly correlated with the phase behavior of these systems. To understand completely the basis for these correlations, one must be able to represent the phase behavior of systems containing surfactants adequately.Surfactant systems for tertiary oil recovery usually contain at least five components: oil, water, surfactant. cosurfactant, and electrolyte. The isothermal, isobaric phase diagram of these systems can be represented in a phase diagram of these systems can be represented in a four-dimensional space. Because physical representation (in three dimensions) of such a diagram is impossible. various techniques have been developed to attempt to represent the phase behavior in lower dimensional spaces. All these techniques correspond to projections of the original diagram onto lower dimensional spaces. Although almost unlimited methods of projection exist, only a small fraction convey useful information.Two projection schemes having some similarities but different intents and consequences are straight mathematical projection and "pseudocomponent" projection. Straight mathematical projection refers to the process of directly projecting the four-dimensional data for the entire phase diagram along some specified direction onto a three-dimensional space. All information parallel to the direction of the projection is lost. For example, if the rays of projections are parallel to the oil/water edge of the phase diagram, the resulting representation contains no information about the relative amounts of oil and water in the phases. In principle, this problem can be circumvented by generating two representations corresponding to projections of the same data along two different directions. For example. a second representation could be produced corresponding to a projection parallel to the water/alcohol edge of the phase diagram. parallel to the water/alcohol edge of the phase diagram. Although neither representation contains complete information, the pair of representations does contain all information about the system. The problem with this method is that the information is not perceived easily and, since the intent of using phase diagrams is usually to make visible a summary of the phase trends, such mathematical representations are not very useful.The second and generally more useful projection scheme uses pseudocomponents. A pseudocomponent is some mixture of pure components treated as a single component. SPEJ P. 289

scholarly journals Prediction of asphaltene precipitation upon injection of various gases at near-wellbore conditions: A simulation study using PC-SAFT EoS

2019 ◽  
Vol 74 ◽  
pp. 63 ◽  
Author(s):  
Saba Mahmoudvand ◽  
Behnam Shahsavani ◽  
Rafat Parsaei ◽  
Mohammad Reza Malayeri
Keyword(s):  
Phase Behavior ◽  
Oil Recovery ◽  
Gas Injection ◽  
Drop Out ◽  
Maximum Point ◽  
Asphaltene Precipitation ◽  
Wide Range ◽  
Tertiary Oil Recovery ◽  
The Impact ◽  
Oil Type

The depletion of oil reservoirs and increased global oil demand have given impetus to employ various secondary and tertiary oil recovery methods. Gas injection is widely used in both secondary and tertiary modes, though the major problem associated with this process is the precipitation and deposition of asphaltene, particularly at near-wellbore conditions. In-depth knowledge of asphaltene phase behavior is therefore essential for the prediction of asphaltene precipitation. Previous studies reported the impact of gas injection on asphaltene phase behavior, but the knowledge of precipitation of asphaltene as a function of different mole fractions of injected gas is also imperative. In this study, the thermodynamic model of PC-SAFT EoS is used to discern the phase equilibrium of asphaltene by analyzing the asphaltene drop-out curve during gas injection. Asphaltene drop-out curves of two different live oil samples are analyzed by injecting CO2, CH4, and N2 gases at different mole percentages and temperatures. The results revealed that PC-SAFT EoS can serve as a reliable tool for estimating bubble pressure and asphaltene onset pressure for a wide range of temperatures, pressures, and compositions. The simulation results for the injection of CO2, CH4, and N2 also showed that CO2 gas gives minimum asphaltene precipitation. It reduces the size of the drop-out curve or moves it toward higher pressures. CH4 and N2 expand the drop-out curve by raising the upper onset point. CH4 increases the maximum point of the drop-out curve for two types of oil studied (A and B) at two different temperatures. N2 raises the maximum point of oil type “A” by approximately 57% at 395 K, while it has no effect on the maximum point of oil type “B”. In addition, reducing the temperature resulted in either decrease or increase of asphaltene solubility, demonstrating that the impact of temperature on asphaltene precipitation is closely related to the composition of the crude.

The relation of emulsion stability to phase behavior and interfacial tension of surfactant systems

1979 ◽  
Vol 72 (1) ◽  
pp. 161-163 ◽  
Author(s):  
Maurice Bourrel ◽  
Alain Graciaa ◽  
Robert S Schechter ◽  
William H Wade
Keyword(s):  
Interfacial Tension ◽  
Phase Behavior ◽  
Emulsion Stability ◽  
Surfactant Systems

Optimal Injection Policies for Enhanced Oil Recovery: Part 2-Surfactant Flooding

1984 ◽  
Vol 24 (03) ◽  
pp. 333-341 ◽  
Author(s):  
Zohreh Fathi ◽  
Fred W. Ramirez
Keyword(s):  
Oil Recovery ◽  
Return On Investment ◽  
Volumetric Flow Rate ◽  
Commercial Application ◽  
Type B ◽  
Surfactant Flooding ◽  
Tertiary Oil Recovery ◽  
Optimal Injection ◽  
Surfactant Systems ◽  
The Cost

Abstract The optimal control theory of distributed-paranieter systems has been applied to the problem of determining the best injection policy of a surfactant slug for a tertiary oil recovery chemical flood. The optimization criterion is to maximize the amount of oil recovered while minimizing the chemical cost. A steepest-descent gradient method was used as the computational approach to the solution of this dynamic optimization problem. The performance of the algorithm was examined for the surfactant injection in a one-dimensional flooding problem. Two types of interfacial tension (IFT) behavior problem. Two types of interfacial tension (IFT) behavior were considered. These are a Type A system where the IFT is a monotonically decreasing function with solute concentration and a Type B system where a minimum IFT occurs at a nominal surfactant concentration. For a Type A system, the shape of the optimal in 'faction strategy was not unique, however, there is a unique optimum for the amount of surfactant needed. For a Type B system, the shape of the optimal injection as well as the amount injected was unique. Introduction Surfactant recovery systems are being investigated by the petroleum industry as a means of increasing the petroleum supply. Commercial application of any petroleum supply. Commercial application of any surfactant flooding process relies upon economic projections that indicate a decent return on investment. projections that indicate a decent return on investment. Previously. surfactant systems for tertiary oil recovery have been optimized by adjusting concentrations of individual components empirically. Salinity has been shown to be an important variable in surfactant system optimization. The particular choice of surfactant and cosurfactant has been studied by Salager et al. Multivariable optimization of surfactant systems based on minimizing the IFT has been studied by Vinatiere et al. As reported, such an optimization may or may not coincide with optimal oil recovery since low IFT is a necessary. but not a sufficient condition for achieving, high displacement efficiency. Chemical supply and cost are important parts of economic projections. Because of the high cost of chemicals, it is essential to optimize surfactant systems to provide the greatest oil recovery at the lowest cost. In this paper, an optimization surfactant is taken as the minimization of the chemical cost and maximization of the recovered oil. The goal is to determine the best way of injecting a surfactant slug into the reservoir formation. Mathematical Formulation of the Performance Index Performance Index We desire to obtain maximum oil recovery with a minimum amount of chemical surfactant injected. These objectives can he expressed in a quantitative form through the formulation of a cost functional. J', which is to be minimized, where J' equals the cost of surfactant injected minus the value of oil recovered. This descriptive statement of the cost functional must be translated into a mathematical form to use quantitative optimization techniques. The oil value can be formulated as (1) where C1 = cost of oil per unit volume ($251.6/m 3[$40/bbl]),= volumetric flow, rate of oil at the coreoutlet L = core length, and a = time. The chemical cost is expressed mathematically as (2) where C2 = chemical cost per unit weight ofsurfactant ($5.45 × 10–3/g [$2.47/lbm]), Cs( ) = surfactant concentration of the injectedfluid in weight fraction, P slug = slug density ( 1 g/cm 3 ). and Qw, ( ) = volumetric flow rate of water at thecore inlet. The objective functional is, therefore, (3) JPT P. 333

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

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

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