Surfactant loss

Alkaline agents can reduce surfactant losses and permit the use of low concentrations of surfactants. Laboratory tests show that alkali and synthetic surfactants produce interfacial properties that are more favorable for increased oil mobilization than either alkali or surfactant alone [639,640]. 

Micellar flooding is a promising tertiary oil-recovery method, perhaps the only method that has been shown to be successful in the field for depleted light oil reservoirs. As a tertiary recovery method, the micellar flooding process has desirable features of several chemical methods (e.g., miscible-type displacement) and is less susceptible to some of the drawbacks of chemical methods, such as adsorption. It has been shown that a suitable preflush can considerably curtail the surfactant loss to the rock matrix. In addition, the use of multiple micellar solutions, selected on the basis of phase behavior, can increase oil recovery with respect to the amount of surfactant, in comparison with a single solution. Laboratory tests showed that oil recovery-to-slug volume ratios as high as 15 can be achieved [439]. 

B. Gall. Use of sacrificial agents to reduce carboxymethylated ethoxy-lated surfactant loss during chemical flooding Topical report. US DOE Fossil Energy Rep, 1989. 

P. Somasundaran. Surfactant loss control in chemical flooding spectroscopic and calorimetric study of adsorption and precipitation on reservoir minerals—annual report for the reporting period September 30, 1992 to September 30, 1993. US DOE Fossil Energy Rep DOE/BC/14884-5, Columbia Univ, 1994. 

The present study suggests the potential application of a method for reducing surfactant losses in reservoirs, thus, ipso facto increasing their effectiveness. This method consists in incorporating a suitable desorbent in the water used to drive the surfactant slug injected into the formation to be treated. 

Oil recovery increases with an increase in micellar slug size. But the process efficiency drops and the surfactant loss increases. 

Dekker et al. [170] have also shown that the steady state experimental data of the extraction and the observed dynamic behavior of the extraction are in good agreement with the model predictions. This model offers the opportunity to predict the effect of changes, both in the process conditions (effect of residence time and mass transfer coefficient) and in the composition of the aqueous and reverse micellar phase (effect of inactivation rate constant and distribution coefficient) on the extraction efficiency. A shorter residence time in the extractors, in combination with an increase in mass transfer rate, will give improvement in the yield of active enzyme in the second aqueous phase and will further reduce the surfactant loss. They have suggested that the use of centrifugal separators or extractors might be valuable in this respect. 

Operation andEunction. Overheating electrocleaner solutions can result in surfactant loss, as for soak cleaners. Tank construction and electrodes can be steel. Current distribution is easier to optimize and control when the inside of the electrocleaner tank is lined with an inert, nonconductive lining. An overflow weir, sump, and recirculating pump are recommended. When plating barrels are used electrocleaning can take 10 minutes or more compared to 1 minute on... 

Adsorption of surfactants "Loss from solution" method, direct measurement using radioactive tracers, ellipsometry, nephelometry... 

Rouse, J. D., Sabatini, D. A., and Harwell, J. H. (1993). Minimizing Surfactant Losses Using Twin Head Anionic Surfactants in Subsurface Remediation. Environmental Science and Technology, 27, 2072-2078. 

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). 

To be a promising candidate for CO2 foam, the surfactant loss by adsorption, partitioning and emulsion formation must be low. In general, anionic surfactants have low adsorption on sandstones and high adsorption on carbonates, whereas the reverse is true for nonionics ( ). Cationic surfactants are not considered because of their high adsorption on many surfaces. 

Figure 5 shows the results of a typical surfactant transport study in a 2 ft long Berea sandstone core. The AEGS 25-12 surfactant, injected at 0.05 wt%, had a low loss on Berea sandstone of 0.008 meq/100 gm rock compared to -0.05 meq/100 gm for typical petroleum sulfonates used in chemical flooding. Surfactant breakthrough occurred at 0.62 PV (Sorw =0.38 PV). The surfactant concentration is consistent with about 10% transport with the brine front. Surfactant loss and transport were monitored using the hyamine titration technique. 

Ideally, the injected micellar solutions will be miscible with the fluids that they are in contact with in the reservoir and can thus miscibly displace those fluids. In turn, the micellar solutions may be miscibly displaced by water. Highest oil recovery will result if the injected micellar solution is miscible with the reservoir oil. If there are no interfaces, interfacial forces that trap oil will be absent. Injection of compositions lying above the multiphase boundary initially solubilizes both water and oil and displaces them in a misciblelike manner. However as injection of the micellar solution progresses, mixing occurs with the oil and brine at the flood front, and surfactant losses occur because of adsorption on the reservoir rock. These compositional changes move the system into the multiphase region. The ability of... 

Indicators of emulsion aging that may be monitored include droplet size growth, viscosity decline, surfactant loss, and reduction of shear stability. 

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. 

In summary, several phenomena occurring at the optimal salinity in relation to enhanced oil recovery by macro- and microemulsion flooding are schematically shown in Figure 18. It is evident that the maximum in oil recovery efficiency correlates well with various transient and equilibrium properties of macro- and microemulsion systems. We have observed that the surfactant loss in porous media is minimum at the optimal salinity presumably due to the reduction in the entrapment process for the surfactant phase. Therefore, the maximum in oil recovery may be due to a combined effect of all these processes occurring at the optimal salinity. 

Control of surfactant retention in the reservoir is one of the most important factors in determining the success or failure of a surfactant flooding project. In a typical surfactant flood, chemical cost is usually half or more of the total project cost. Based on the mechanisms, surfactant retention can be broken down into precipitation, adsorption, and phase trapping. However, it is difficult to separate the surfactant losses from different mechanisms. Therefore, we usually report the total surfactant loss as surfactant retention without clearly specifying the losses from different mechanisms. 

In a surfactant-polymer process, Trushenski (1977) reported that the presence of polymer in the surfactant slug caused an unexpected increase in surfactant loss. This increase was due to the bypass of surfactant by polymer (phase trapping). The trapping and remobilization of the micellar phase are shown in Figure 9.3. In this long core test, the water content of the micellar fluid was... 

In this connection, considering the potential problem of surfactant loss to the apparatus, we remark that the procedure of an initial flow of sample water through the tensiometer vessel is mandatory in all circumstances when the concentration of soluble or almost-insoluble surfactants is very low. Actually, at first significant amounts of the surfactants become lost via adsorption onto the glass-vessel walls or loss of material due to adsorption at the bubble surface (Miller 2004). Consequently, the water flow through the vessel should continue until the adsorption equilibrium is reached. The instrument proved to be relatively insensitive to vibrations, as reported by Loglio et al. (1998b). Thus, the observed functionality, inside the onshore laboratory, may likely be fulfilled on a platform-based location, too. 

It is commonly known that the constituents of a micellar slug may interact in several ways with both the rock and the formation fluids when injected into a reservoir, and a considerable body of literature exists (1-8). In spite of this knowledge, however, it is not yet possible to design a micellar slug for tertiary oil recovery from basic principles because of the complexity of the phenomena and inadequate understanding of the processes involved. The primary objectives of this paper are to present the results of some experiments on the structure and mineralogy of selected rock and reservoir core samples, on the interactions within surfactant solutions and between surfactant solutions and rock, and to attempt to draw from these observations some conclusions as to the phenomena and mechanisms involved-especially surfactant loss processes-as these can affect the maintenance of low interfacial tension between oil and water. 

More recently Smith (8), and Hill and Lake (14) studied cation exchange as it affected the behavior of micellar slugs in typical reservoir cores. These authors found that cation exchange in cores was quite complex, but that calcium and magnesium could, for all practical purposes, be treated as a single species. Moreover, they found that pre-flushing of a core reduced surfactant losses in most cases. Hill and Lake found that surfactant adsorption in cores was reduced by dissolution of carbonate minerals and by converting the clays to their sodium form. 

The point of zero charge of the reservoir minerals, their physical structure, the surfactant equivalent weight and structure, and the structure of the electrical double layer at the solid/solution interface appear to be major factors determining the mechanism of adsorption and potential surfactant losses in surfactant flooding. 

Both the effectiveness and the economics of steam-foam processes depend critically on surfactant losses, and it is therefore essential to minimize losses due to the chemical and physical phenomena occurring in the reservoir at elevated temperatures. 

Both the precipitation and partitioning of anionic surfactants increase with increasing temperature. For a C16—Clg alkylaryl surfactant, such as Suntech IV, surfactant losses due to partitioning were in the range... 

Shell (48) used a simple foam model (49) for their Bishop Fee pilot. The foam generation rate was matched by using an effective surfactant partition coefficient that took into account surfactant losses and foam generation inefficiencies. The value of this coefficient was selected so that the numerical surfactant propagation rate was equal to the actual growth rate. Foam was considered to exist in grid blocks where steam was present and the surfactant concentration was at least 0.1 wt%. The foam mobility was assumed to be the gas-phase relative permeability divided by the steam viscosity and the MRF. The MRF increased with increasing surfactant concentration. The predicted incremental oil production [5.5% of the... 

The following mechanisms are usually major contributors to surfactant loss in an oil-free porous medium ... 

Surfactant solubility and chemical stability are more easily assessed and controlled by proper surfactant selection than adsorption at the solid—liquid interface. In principle, proper foam-flood design should completely eliminate surfactant loss caused by the first two mechanisms. The... 

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