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

Optimal Injection Strategies for the Propagation of Surfactant Mixtures Through Porous Media

1984 ◽  
Vol 24 (05) ◽  
pp. 545-554 ◽  
Author(s):  
Jeffrey H. Harwell ◽  
Robert S. Schechter ◽  
William H. Wade
Keyword(s):  
Molecular Weight ◽  
Porous Media ◽  
Oil Recovery ◽  
Chromatographic Separation ◽  
Surfactant Solution ◽  
Commercial Application ◽  
Recovery Efficiency ◽  
Surfactant Mixtures ◽  
Optimal Injection ◽  
Injection Strategies

Abstract The chromatographic movement of surfactant mixtures through porous media is examined to determine possible injection strategies for minimizing the amount of surfactant required in a tertiary oil recovery chemical flood. The model used does not consider the presence of oil but does account for mixed micelle formation. Expressions are derived that represent the surfactant required to expose an entire reservoir to an "effective oil recovery mixture." This effective mixture may be either one whose overall composition is within prescribed limits of the composition of the injected surfactant solution or it may be a mixture whose overall composition varies but which contains micelles of fixed composition. Mixtures considered contain cosolvents and one, two, or three surfactant components. Initial calculations neglect dispersion, but numerical calculations including dispersion leave the conclusion unchanged; within the limitations of the model, there are optimal strategies for the propagation of surfactant mixtures through porous media. The optimal injection strategy varies, depending on the nature of the surfactant solution injected into the porous medium. Conditions for and the location of the optimum are discussed. Conclusions based on observations about these systems then are extended to cover the injection of surfactant mixtures currently available commercially. Introduction Commercial application of surfactants for EOR now appears feasible. The principle at work in such processes is the lowering of interfacial tension (IFT) between the continuous flowing water and trapped residual oil droplets to allow the oil to be mobilized. Mixtures that effectively lower oil/water IFT are often blends of various surfactant types, isomers of the same surfactant, and/or cosurfactants in an electrolyte solution. The oil recovery efficiency of the injected mixture generally is quite sensitive to changes in mixture composition. Change of composition after injection into the reservoir may occur by one or a combination of mechanisms. For example, the mixture components may partition selectively into the various phases present in the reservoir. The mechanism considered here is the chromatographic separation of the mixture into its components due to preferential adsorption of various components onto reservoir minerals-"the chromatographic problem." The recent reports of the Bell Creek Unit A micellar/polymer pilot showed 20% of the injected surfactant produced before any oil bank with negligible concomitant incremental tertiary oil production. Significantly, the surfactants produced were the lower-molecular-weight species. Though alternative mechanisms for this separation yet may be established, the hypothesis of chromatographic separation of the components in the mobile aqueous phase seems adequate. Not only did this produced surfactant not result in enhanced recovery, but since the injected solution was designed to give ultralow IFT's with the low-molecular-weight components in place, it seems likely that the oil recovery efficiency of the remaining surfactant also may have been impaired. These results emphasize the importance of understanding the mechanisms of surfactant chromatographic movement. One means of combatting the chromatographic problem is to reduce the local adsorption of the mixture components-that is, modify the adsorption isotherms of the constituents. This may be done either by changing the reservoir minerals (e.g., by a caustic flood) or by modifying the structure of the surfactant molecules. A complementary approach is to examine the dynamics of the chromatographic movement of surfactant mixtures to identify injection strategies, if they exist, that minimize the total surfactant requirement. It is this question that is considered here. The analysis considers an oil-free linear system and neglects many of the complex features that are encountered in an actual chemical flood. There are several reasons for ignoring these complicating factors. The coherence solutions apply to the systems considered here; whereas the only solutions that include the presence of oil employ numerical computations. An analytical solution is desirable; however, there is an additional more compelling argument that has been used to justify neglecting the presence of oil. The chromatographic movement of a surfactant/ cosurfactant mixture through an oil-free core should demonstrate the qualitative features of the actual oil recovery process. While multiple flowing phases do arise in an actual flood, the released oil forms a bank ahead of the surfactant slug. SPEJ P. 545^

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.

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

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

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

Research on the Effect of Movable Gel Flooding after Polymer Flooding

2014 ◽  
Vol 672-674 ◽  
pp. 723-726
Author(s):  
Rong Wei Liu
Keyword(s):  
Oil Recovery ◽  
Polymer Flooding ◽  
Economic Feasibility ◽  
Main Function ◽  
Sweep Efficiency ◽  
Profile Modification ◽  
Injection Process ◽  
Tertiary Oil Recovery ◽  
Gel Injection ◽  
The Cost

The experiments on microscopic displacement of flowing gel flooding after water and polymer flooding were carried out with the sand-packing model. The experimental results of the microscopic displacement indicate that oil recovery can be further enhanced using flowing gel after water and polymer flooding, and the enhanced range is about 15 percent. Flowing gel flows preferentially through the largerchannels occupied previously by injected water in flowing gel injection process, improves sweep efficiency of injected water. Because of its viscoelastic, it can be stretched through the narrow pore deformation. The strength was reduced by the shear, dilution, and it would be driven out by the water from the pores and continue to move forward. Therefore, the main function of flowing gel is flooding, while profile modification is temporary effect. Flowing gel flooding can significantly reduce the cost of chemicals. From the development of tertiary oil recovery trend, flowing gel flooding is a technology that is being developed and perfected, with high technology-economic feasibility.

Investigation into the Functions of Alkali and Surfactant in Chemical Flooding for Enhanced Heavy-Oil Recovery

2012 ◽  
Vol 524-527 ◽  
pp. 1816-1820 ◽  
Author(s):  
Ji Jiang Ge ◽  
Hai Hua Pei ◽  
Gui Cai Zhang ◽  
Xiao Dong Hu ◽  
Lu Chao Jin
Keyword(s):  
Oil Recovery ◽  
Heavy Oil ◽  
Chemical Flooding ◽  
Surfactant Flooding ◽  
Core Flooding ◽  
Sweep Efficiency ◽  
Water Emulsion ◽  
Tertiary Oil Recovery ◽  
Fingering Phenomena ◽  
Oil In Water Emulsion

In this study, a comparative study of alkaline flooding and alkali-surfactant flooding were conducted for Zhuangxi heavy oil with viscosity of 325 mPa•s at 55 °C. The results of core flooding tests show that the tertiary oil recovery of alkali-surfactant flooding are lower than those of alkaline-only flooding, in spite of the coexistence of the surfactant and alkali can reduce the IFT between the heavy oil and aqueous phase to an ultralow level. Further flood study via glass-etching micromodel tests demonstrates that injected alkaline-only solution can penetrate into the oil phase and creates some discontinuous water droplet inside the oil phase that tend to lower the mobility of the injected water and lead to the improvement of sweep efficiency. While for alkali-surfactant flooding, heavy oil is easily emulsified in brine by an alkaline plus very dilute surfactant formula to form oil-in-water emulsion, and then entrained in the water phase. Therefore, viscous fingering phenomena occur during the alkali-surfactant flooding, resulting in relatively lower sweep efficiency.

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