Surfactant flooding discussion

Emulsion characterization and technology development have been driven by the medical, agricultural, food, and cosmetics industries the petroleum and oil industries have borrowed these technologies and adapted them to their particular applications. A number of books and review articles discuss aspects of emulsion technologies specifically related to oil-field and petroleum applications 14, IS), These petroleum applications have become especially important since the advent of surfactant flooding and other tertiary oil recovery methods in which emulsions are used and/or formed. 

It was observed that the formulations consisting of ethoxylated sulfonates and petroleum sulfonates are relatively insensitive to divalent cations. The results show that a minimum in coalescence rate, interfacial tension, surfactant loss, apparent viscosity and a maximum in oil recovery are observed at the optimal salinity of the system. The flattening rate of an oil drop in a surfactant formulation increases strikingly in the presence of alcohol. It appears that the addition of alcohol promotes the mass transfer of surfactant from the aqueous phase to the interface. The addition of alcohol also promotes the coalescence of oil drops, presumably due to a decrease in the interfacial viscosity. Some novel concepts such as surfactant-polymer incompatibility, injection of an oil bank and demulsification to promote oil recovery have been discussed for surfactant flooding processes. 

The main objective of surfactant flooding is to reduce residual oil saturation, which is closely related to capillary number. Therefore, the concept of capillary number is discussed first. Analysis of the pore-doublet model yields the following dimensionless grouping of parameters (Moore and Slobod 1955), which is a ratio of the viscous-to-capillary force ... 

Relative permeability is probably one of the least-defined parameters in chemical flooding processes. The classical relative permeability curves represent a situation in which the fluid distribution in the system is controlled by capillary forces. When capillary forces become small compared to viscous forces, the whole concept of relative permeability becomes weak. This area has not been adequately researched, and theoretical understanding is rather inadequate (Brij Maini, University of Calgary in Canada, personal communication, 2007). This section discusses relative permeability models related to surfactant flooding and the IFT effect on relative permeabilities. 

Theories of surfactant flooding and polymer flooding are discussed in Chapters 5 to 7. This chapter focuses on surfactant-polymer (SP) interactions and compatibility. Optimization of surfactant-polymer injection schemes is also discussed. The methodology and even some conclusions in the presented optimization may be applied to other processes as well. Finally, this chapter presents a field example. 

For oil displacement purposes, alkali can be co-injected with any displacing agents except an acid or carbon dioxide. For example, aUcaline-polymer (AP), alkaline-surfactant (AS), aUcaline-gas, alkaline-steam, aUcaline-hot water, and more can be used. This chapter discusses alkaline-surfactant flooding. 

Chapter 7 discusses the fundamentals, concepts, and issues related to surfactant flooding. 

Ultra-low tension In the alkaline flooding of acidic acids, some reduction in interfacial tension (from 30 to approximately 10 1 dynes/cm) is necessary for the emulsification and subsequent mobilization of waterflooded residual oil by the previously discussed phase alteration mechanisms. The residual oil may also be mobilized and produced by a low-tension displacement process which is similar to surfactant flooding if the interfacial tension can be further reduced to ultra-low values (10 to 10 dynes/cm). 

Anionic Blends onto Sand and Clay. Following a successful enhanced oil recovery demonstration using a surfactant blend in a foam flood, research was conducted to examine the fate of the blends in core studies [6J], The surfactant blend was composed of alpha olefin sulfonates (AOS s) and the DOWFAX surfactant 3B2. This surfactant is a disulfonated alkyldiphenyloxide (DPOS). This line of surfactants is discussed in more detail in the third part of this section. 

Conventional pump-and-treat techniques are not very effective in restoring aquifers impacted by DNAPLs. This ineffectiveness is a result of the relatively low solubility of the DNAPL and the large capillary forces that immobilize the nonaqueous phase. Over the past decade, several innovative and experimental strategies have been tested for more effective recovery of DNAPLs. These strategies include the more conventional use of surfactants, and thermally enhanced extraction or steam injection. Other more experimental approaches include cosolvent flooding and density manipulations. Each of these approaches is discussed below. 

Since a sequence of dispersion structures in bulk dispersions has been correlated with flooding results, the dependence of dispersion structure on phase behavior is also briefly reviewed. This leads to a discussion of phase behavior and its dependence on surfactant structure and other thermodynamic parameters. 

Micellar-polymer flooding and alkali-surfactant-polymer (ASP) flooding are discussed in terms of emulsion behavior and interfacial properties. Oil entrapment mechanisms are reviewed, followed by the role of capillary number in oil mobilization. Principles of micellar-polymer flooding such as phase behavior, solubilization parameter, salinity requirement diagrams, and process design are used to introduce the ASP process. The improvements in ""classicaV alkaline flooding that have resulted in the ASP process are discussed. The ASP process is then further examined by discussion of surfactant mixing rules, phase behavior, and dynamic interfacial tension. 

The physicochemical aspects of micro- and macroemulsions have been discussed in relation to enhanced oil recovery processes. The interfacial parameters (e.g. interfacial tension, interfacial viscosity, interfacial charge, contact angle, etc.) responsible for enhanced oil recovery by chemical flooding are described. In oil/brine/surfactant/alcohol systems, a middle phase microemulsion in equilibrium with excess oil and brine forms in a narrow salinity range. The salinity at which equal volumes of brine and oil are solubilized in the middel phase microemulsion is termed as the optimal salinity. The optimal salinity of the system can be shifted to a desired value hy varying the concentration and structure of alcohol. 

In this section, several important aspects of microemulsions in relation to enhanced oil recovery will be discussed. It is well recognized that the success of the microemulsion flooding process for improving oil recovery depends on the proper selection of chemicals in formulating the surfactant slug. 

Surfactants in Remediation. Although surfactant use in enhanced oil recovery has been explored in some detail, its use as a remedial flooding technique is still in the preliminary experimental stages, and few studies are available in the literature to date. Examples of some studies are discussed here. 

When surfactant solution is injected in a reservoir, it contacts with oil to form three types of microemulsion, depending on the local salinity. Here, we discuss only the fractional curve analysis of Winsor 1 microemulsion. For a discussion of fractional flow of Winsor 11 without retention, see Lake (1989). Fractional flow treatment for three-phase microemulsion flood (Winsor III) has not been extensively investigated (Giordano and Salter, 1984). 

This section discusses how to select the parameters to calculate capillary number. Initially, capillary number was proposed to correlate the residual saturation of the fluid (oil) displaced by another fluid (water) in the two-phase system. In surfactant-related flooding, there is multiphase flow (water, oil, and microemulsion), especially at the displacing front. If we use up/a to define the relationship between capillary number and residual oil saturation, which phase u and p and which o should be used then To the best of the author s knowledge, this issue has not been discussed in the literature. The following is what we propose. 

During a polymer flood, because of polymer adsorption, a polymer denuded zone forms at the front of polymer slug. If a surfactant slug is injected ahead of a polymer slug, however, adsorption sites are occupied by surfactant. In some cases, polymer loss is reduced to an insignificant level owing to the so-called competitive adsorption, discussed earlier. Thus, a polymer denuded zone may... 

The purpose of an activity map is to show at what range of concentrations in a system and how a chemical flood will work. For a given reservoir where the temperature, composition of crude oil, and residual oil saturation are fixed, five kinds of variables are under our control types of alkalis, concentrations of alkalis, types of surfactants, concentrations of surfactants, and salinity. Another important variable that is not under our direct control is the type and amount of petroleum acid that will convert to soap when contacted by the alkalis. As discussed earlier, the amount of soap will determine the concentrations of alkali and surfactant injected. In other words, to generate an activity map, we have to know the amount of soap that can be generated. Because the alkali concen-ttation typically is much greater than that required to convert all the petroleum acids in the oil to soap, the petroleum soap concentration (meq/L) is calculated... 

Synergy is discussed in previous chapters. Here, we provide extra evidence to demonstrate the synergy in ASP. Core samples were waterflooded to residual oil saturation and then injected with polymer, alkaline-polymer (AP), or ASP. The results, in Table 13.1 (Ball and Surkalo, 1988), show that adding alkali further reduced residual oil saturation by 0.137, compared with polymer flooding. Through the further addition of only 0.1 wt.% surfactant, an additional 0.136 residual oil saturation was reduced. In these samples, ASP was the most efficient approach, demonstrating the synergy of alkali, surfactant, and polymer floods. 

This book is written mainly for petroleum professionals. Because overwhelming parameters are needed to describe a chemical EOR process, it is not practical to measure every one of them therefore an effort has been made to collect, synthesize, and suimnarize available data, especially Chinese information that is inaccessible in Western literature. An effort has also been made to cover comprehensively the fundamental theories and practices related to alkaline (A), surfactant (S), and polymer (P) flooding processes, especially alkaline-surfactant-polymer (ASP) flooding that has barely been discussed in any enhanced oil recovery book in English. 

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