Surfactant slug

Process effectiveness depends on maintaining an ultralow (ca 10 ° N/m (10 dynes/cm)) interfacial tension between the injected surfactant slug and the cmde oil (213). The effect of petroleum composition on oil solubilization by surfactants has been the subject of extensive study (214). 

Begin drilling. After 5 or 10 ft have been drilled, the hole should dust (although it is sometimes necessary to drill 60 to 90 ft before dust appears at the surface). If the hole does not dust after these steps have been carried out, pump another surfactant slug around. If dusting cannot be achieved, mist drilling may be required to complete the operation. 

The present study investigates the adsorption and trapping of polymer molecules in flow experiments through unconsolidated oil field sands. Static tests on both oil sand and Ottawa sand indicates that mineralogy plays a major role in the observed behavior. Effect of a surfactant slug on polymer-rock interaction is also reported. Corroborative studies have also been conducted to study the anomalous pressure behavior and high tertiary oil recovery in surfactant dilute-polymer systems(ll,12). 

As a test, surfactant slug flow experiments were performed in clayey sandpacks with and without the injection of a desorbent behind the micellar slug. Results show that a substantial decrease in surfactant retention is obtained in calcic environment by such an additive. Likewise, the ethoxylated cosurfactant in the micellar slug can be remobilized simultaneously with sulfonatewithout any change in its ethylene oxide distribution. The application of the RST to sulfonate/ ethoxylated alkylphenol mixtures explains semi-quantitatively the relationship between their properties and composition. 

Elution of a Surfactant Slug in the Presence of a Desorbent A mass balance for each of the three additives was used to and results obtained during each test are given in Table HI. 

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. 

Injection of surfactant slugs alone did not spontaneously produce macroemulsions which would significantly lower the permeability of the cores. Sometimes subsequent injection of an inert gas produced an oil-in-water emulsion that was part of the liquid phase of the foam. 

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. 

As the surfactant slug is injected into the reservoir, the mixing of injected slug with reservoir components takes place. The mixing of surfactant with reservoir oil and brine often produces emulsions. Moreover, the reservoir parameters such as porosity, pressure, temperature, composition of connate water and crude oil as well as gas-oil ratio affect the formation of oil field emulsions. 

Surfactant-polymer flooding involves successive injections into the reservoir of an aqueous surfactant-cosurfactant solution and a dilute aqueous solution of a high molecular weight polymer. The primary purpose of the surfactant slug is to reduce the interfacial... 

The efficiency and economics of oil recovery can be adversely affected by interactions between surfactant aggregates and polymer. Such interactions occur because of mixing at the boundary between surfactant and buffer solutions, and because residual surfactant adsorbed on the rock surface may later desorb into polymer solution. Mixing of polymer and surfactant may also occur throughout the surfactant bank because of the "polymer inaccessible pore volume" effect (1 ). Large polymer molecules are excluded from the smaller pores in the reservoir rock, and travel faster than the surfactant. Thus, polymer molecules enter into the surfactant slug. 

Gupta and Trushenski (1979) found that the most significant factor controlling oil recovery was the salinities of polymer and surfactant slugs (high oil recovery... 

Effect of Relative Permeabilities (K Curves) in a Finite Surfactant Slug... 

Based on Cases krl to kr4, we change the surfactant slug size from 0.1 PV to 0.2 PV, and the concentration from 3% to 1.5%. We also move 0.2 PV polymer into the surfactant slug. The resulting cases are II to 14. In these cases, we start... 

In these cases, the oil viscosity is reduced by 25 times to such a low value as 0.2 mPa s. We suspect that the velocity effect could be the dominant effect. Even if the velocity effect is important, it certainly can be reduced or eliminated when polymer is added in the surfactant slug in surfactant-polymer flooding. 

Immediately after the surfactant sing, a polymer or water drive slug with the same optimum salinity mnst be nsed as a salinity guard to make sure that salinity dispersion and diffnsion cannot change the optimum salinity in the surfactant slug. 

In Case OSPl, the salinity in the chase water after the guard slug (polymer slog) is 0.335 meq/mL. Because the slug before the surfactant slug is not... 

For the optimum salinity, in the cases krl to kr5, the optimum phase type is type II(+) in Case kr2, not type III in Case krl, and the optimum salinity is 0.415 meq/mL, not the conventional optimum salinity of 0.365 meq/mL at the middle of Csd and Cse . In Case OSP7, we keep the optimum salinity of 0.415 meq/mL in the 0.4 PV polymer slug after the surfactant slug and in the preflush water, but change the salinity in the chase water from 0.415 to 0.335 meq/mL. Thus, the salinity profile follows the proposed optimum salinity prohle. The RF from this case is higher than the RF from Case kr2, and actually higher than any RF from Cases krl to kr5. In other words, the RF from the OSP case is the highest. 

One important point in the proposed OSP is that the salinity in the chase slug after the guard slug in OSP must be lower than Csei. One of the main mechanisms to justify such salinity is surfactant desorption. Liu et al. (2004) found that, in an extended waterflood following an alkaline-surfactant slug... 

Because the multiplier Esp is always less than or equal to 1, the maximum surfactant adsorption is reduced or unchanged. Note that if a surfactant slug is injected ahead of a polymer slug, some adsorption sites are covered by... 

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... 

There is another phenomenon that is called polymer inaccessible pore volume (IPV). Laboratory data indicate that inaccessible pore volume is usually greater than the adsorption loss for polymers following a micellar solution (Trushenski et al., 1974). The competitive adsorption and IPV may make polymer penetrate the surfactant slug ahead of it. Therefore, surfactant-polymer interaction or incompatibility occurs not only in the surfactant-polymer process where the surfactant and the polymer are injected in the same slug, but also in the surfactant-polymer process where surfactant is injected before the polymer slug. 

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... 

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