Mobility-control surfactants

Mobility control, issues in, 18 626 Mobility control agents polyacrylamides as, 18 625 in polymer flooding, 18 622 Mobility control surfactants, in enhanced oil recovery, 18 625-628 Mobilizable vectors, for genetic manipulation, 12 471 Mobilization, of ascorbic acid, 25 771 Modacryhc fibers, 9 192 11 188, 189, 190 dyesite content of, 11 195 flame resistance of, 11 214 flammability of, 11 194 pigmented, 11 213 U.S. production of, 11 220t Mode conversion phenomenon, 17 422 Model agreements, 24 373-374 Model-based methods, for reliability, 26 1044... 

By improving "sweep" and "mobility control," surfactant-based methods offer the most promising ways to alleviate these problems. This use of surfactants appears to be just on the verge of commercialization for steam flooding. Because miscible CO2 flooding has been commercialized more recently, the use of surfactants to improve gas-flood EOR has not yet been commercialized. Conceivably, however, the long-term viability of gas flooding could prove to be dependent on the success of current research efforts in the use of surfactants to alleviate "bypass" problems. 

In surfactant-based mobility control, surfactant adsorption is important in at least four ways ... 

The development of a rational strategy of surfactant design requires some way of estimating the dependence of phase parameters on surfactant structure and reservoir characteristics (e.g., salinity). Chapter 9, by Borchardt, describes a method for correlating phase and physical properties of mobility control surfactants with their molecular structures. 

Structure—Property Relationships for Mobility-Control Surfactants... 

The surfactant systems used for mobility control in miscible flooding do not form a surfactant rich third phase, and lack its buffering action against surfactant adsorption. Furthermore, for obvious economic reasons, it is desirable to keep the surfactant concentration as low as possible, which increases the sensitivity of the dispersion stability to surfactant loss. Hence, surfactant adsorption is necessarily an even greater concern in the use of foams, emulsions, and dispersions for mobility control in miscible-flood EOR. The importance of surfactant adsorption in surfactant-based mobility control is widely recognized by researchers. A decision tree has even been published for selection of a mobility-control surfactant based on adsorption characteristics (12). 

The CT images identified several mechanisms that help to explain how mobility-control surfactant causes CO2 to be stable against both gravity and viscous forces during tertiary miscible core flow experiments. 

The mobility-control surfactant increased the apparent viscosity of CO2 sufficiently to prevent gravity override and viscous fingering. The bulk CO2 phase passed through the core in a piston-like manner. Oil and most of the brine were displaced from the core ahead of the bulk-phase CO2. Differential pressure measurement across the length of the core indicated an average gradient, 1.3 psi/ft, similar to that observed during the brine flood. 

The salinity of poljmier solution can influence four major parameters of surfactant-pol)mi r flooding process, namely, interfacial tension, mobility control, surfactant loss and phase behavior. When polymer solution of various salinities are equilibrated with surfactant solution in oil, the formation of lower, middle and upper phase microemulsion has been observed (1) similar to the effect of increasing connate water salinity (2,3). In general, there is an optimal salinity (2) which produces minimum interfacial tension and maximal oil recovery (1,4). On the basis of interfacial tension alone, the salinity of polymer solution should then be designed at or near the optimal salinity of the preceding surfactant formulation. 

Surfactants for Mobility Control. Water, which can have a mobihty up to 10 times that of oil, has been used to decrease the mobihty of gases and supercritical CO2 (mobihty on the order of 50 times that of oil) used in miscible flooding. Gas oil mobihty ratios, Af, can be calculated by the following (22) ... 

Polymers can be used for mobility control. The interaction between polymers and surfactants is shown to be affected by pH, ionic strength, crude oil type, and the properties of the polymers and surfactants [642]. 

Water-in-oil macroemulsions have been proposed as a method for producing viscous drive fluids that can maintain effective mobility control while displacing moderately viscous oils. For example, the use of water-in-oil and oil-in-water macroemulsions have been evaluated as drive fluids to improve oil recovery of viscous oils. Such emulsions have been created by addition of sodium hydroxide to acidic crude oils from Canada and Venezuela. In this study, the emulsions were stabilized by soap films created by saponification of acidic hydrocarbon components in the crude oil by sodium hydroxide. These soap films reduced the oil/water interfacial tension, acting as surfactants to stabilize the water-in-oil emulsion. It is well known, therefore, that the stability of such emulsions substantially depends on the use of sodium hydroxide (i.e., caustic) for producing a soap film to reduce the oil/water interfacial tension. 

The low-tension polymer flood technique consists of combining low levels of polymer-compatible surfactants and a polymer with a waterflood. This affects mobility control and reduces front-end and total costs. [929]. 

Xanthan exhibits an interaction with anionic surfactants (petroleum sulfate), which is a beneficial synergistic effect for mobility control in chemical-enhanced oil-recovery processes [1115]. 

Coinjection of a low-concentration surfactant and a biopolymer, followed by a polymer buffer for mobility control, leads to reduced chemical consumption and high oil recovery. There may be synergistic effects between the surfactant and the polymer in a dynamic flood situation. The chromatographic separation of surfactant and polymer is important to obtain good oil recovery and low surfactant retention [1721],... 

Recent research and field tests have focused on the use of relatively low concentrations or volumes of chemicals as additives to other oil recovery processes. Of particular interest is the use of surfactants as CO (184) and steam mobility control agents (foam). Also combinations of older EOR processes such as surfactant enhanced alkaline flooding and alkaline-surfactant-polymer flooding have been the subjects of recent interest. Older technologies polymer flooding (185,186) and micellar flooding (187-189) have been the subject of recent reviews. In 1988 84 commercial products polymers, surfactants, and other additives, were listed as being marketed by 19 companies for various enhanced oil recovery applications (190). 

The reason for wide-spread interest in the use of surfactants as gas mobility control agents (369) is their effectiveness at concentrations of 0.1%wt (377) or less (364). This low chemical requirement can significantly improve process economics. 

In addition to the mobility control characteristics of the surfactants, critical issues in gas mobility control processes are surfactant salinity tolerance, hydrolytic stability under reservoir conditions, and surfactant propagation. Lignosulfonate has been reported to increase foam stability and function as a sacrificial adsorption agent (392). The addition of sodium carbonate or sodium bicarbonate to the surfactant solution reduces surfactant adsorption by increasing the aqueous phase pH (393). 

Surfactants have been used as steam mobility control agents in both laboratory and field tests to prevent this gravity override thereby increasing volumetric sweep efficiency. Surfactants that have been... 

Intermixing of the polymer mobility control fluid with the surfactant slug can result in surfactant - polymer interactions which have a significant effect on oil recovery (476). Of course, oil - surfactant interactions have a major effect on interfacial behavior and oil displacement efficiency. The effect of petroleum composition on oil solubilization by surfactants has been the subject of extensive study (477). 

Smith, D.H. Surfactant-Based Mobility Control - Progress in... 

Petroleum recovery typically deals with conjugate fluid phases, that is, with two or more fluids that are in thermodynamic equilibrium. Conjugate phases are also encountered when amphiphiles fe.g.. surfactants or alcohols) are used in enhanced oil recovery, whether the amphiphiles are added to lower interfacial tensions, or to create dispersions to improve mobility control in miscible flooding 11.21. 

Surfactant-Based Mobility Control Progress in Miscible-Rood Enhanced Oil Recovery Smith, Duane H., Ed. ACS Symposium Series No. 373 American Chemical Society Washington, D.C., 1988. 

When this pressure drops, it can be built-up again by water flooding. Unfortunately, after these primary and secondary processes, there still remains up to 70% of the oil adsorbed on the porous clays. Consequently, in recent years, there have been tremendous efforts made to develop tertiary oil recovery processes, namely carbon dioxide injection, steam flooding, surfactant flooding and the use of microemulsions. In this latter technique, illustrated in Fig. 1, the aim is to dissolve the oil into the microemulsion, then to displace this slug with a polymer solution, used for mobility control, and finally to recover the oil by water injection ( 1). 

Systems in which surfactant precipitate is present in substantial quantities in equilibrium with micelles and monomer are of interest. For example, in a technique for improving mobility control in oil reservoirs, surfactant is purposely precipitated in the permeable region of a reservoir to plug it (44). When substantial precipitate is present, crystals of different composition can be in simultaneous equilibrium. Experimental study and modeling of these systems where several Ksr- relationships are simultaneously satisfied will be a challenging task. 

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