Surfactant slug, aqueous

Fig. 2. The effect of salinity of connate water and polymer solution on tertiary oil recovery by aqueous surfactant slug in sand packs.

Fig. 8. Surfactant concentration in oil and brine, partition coefficient and interfacial tension of effluent fluids of aqueous surfactant slug flooding in Berea cores containing high concentration of CaCl2. The salinity shock design of polymer solution (i.e. two pol3rmer slugs) was used.

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... 

Salinity Salinity plays at least two important roles, namely it maintains the integrity of the reservoir and it balances the physicochemical environment so that surfactant formulation stays close to optimal. Thus, ultra-low interfacial tension and oil solubilisation are very sensitive to salinity. Mixing of the surfactant slug with connate water may alter the surfactant formulation mainly due to dilution and to the incorporation of new electrolytes to the formula. Adsorption and desorption of electrolytes, particularly divalent cations, onto or from solid materials such as clay, will also change the salinity of the aqueous phases to some extent and may cause surfactant precipitation, which is however not always an adverse effect [151]. In order to attenuate the undesirable salinity effects on formulation, surfactants able to tolerate salinity changes [109], high salinity [150] and the presence of divalent ions [112] maybe used. 

When the salinity of pol)nner solution was at the optimal salinity of the preceding surfactant formulation, oil recovery in sand packs was favorable over a wide range of connate water salinities for both aqueous and oleic surfactant formulations. Oil recovery drastically decreased when the salinity of polymer solution was shifted from the optimal salinity even when the connate water was at the optimal salinity. These results indicate that the processes occurring at the surfactant slug-polymer solution mixing zone dominate the oil recovery efficiency. 

The results of the core flooding experiments are summarized in Table 1. In the 30 cm core and in experiment 1, all aqueous solutions (connate water, waterflood, surfactant slug, polymer... 

Generally, the reservoir pressure is not high enough to produce a significant change in the surfactant or polymer slug. However, the oil phase is normally much more compressible than the aqueous phase [132, 149]. Additionally, it may contain some dissolved gases [141]. Therefore, oil density and oil chemical composition maybe quite different from what is observed in the laboratory. Furthermore, the apparent oil equivalent alkane carbon... 

The surfactant has been injected as high-concentration slugs [10 wt% active (35)] or continuously at a lower concentration (0.1—1.0 wt% active). Noncondensible gas (at a concentration of 0.5—1.0 mol% in the gas phase) or NaCl (1—4 wt% in the aqueous phase) may be coinjected with the surfactant and steam in order to stabilize the foam. Figure 4 can be used to estimate the minimum concentration of noncondensible gas required. Extra water may be added to the steam to maintain the liquid volume fraction at the desired value (typically above 0.01). 

The slug of surfactant solution can either be aqueous or oleic with a surfactant plus alcohol concentration of 5-15%. 

Polymer solution was 2000 ppm PUSHER-700 in 2.1% NaCl, 0.4 PV slug followed by 500 ppm in 0.05% NaCl, 0.6 PV slug Soluble oil formulation = 10% TRS 10-410 + 4% IBA in hexa-decane 5% PV slug. Aqueous formulation = 7.65% TRS 10-410 + 3.06% IBA in 2.1% NaCl 5% PV slug. Different concentrations (w/w) of oleic and aqueous formulations were employed to take into account their density difference so that the amount of surfactant and alcohol injected was the same Permeability of the 13" x 1" Berea cores = 200 to 400 milli-Darcy porosity = 22%... 

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