Surfactant flooding calculation

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) ... 

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. 

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... 

Instead of relying completely on theory for the determination of mobility, most researchers also performed experimental measurements of the quantities of interest. Many of the first experiments on foam were performed with water and gas with the outlet at ambient pressure, and many were simply gas floods of packs or cores saturated with surfactant solution. Although for many such transient experiments, the published data were insufficient for the estimation of the steady-state mobilities required for the estimation of mobility-control effectiveness, this was not true for some of them. Calculated values of mobility and relative mobility were derived by Heller et al. (22), from the data published in six different papers (23—28). The values they found, given in terms of relative mobilities, ranged from 0.001 to 0.6 cP-1, or in terms of effective viscosities from 1000 down to 1.6 cP (1 to 0.0016 Pa-s). Not enough information was available to trace all of the relevant parameters that may have caused these differences. 

A core-flood for adsorption determination consists of injecting a measured volume of surfactant solution containing a nonadsorbing tracer into a brine-saturated core and collecting effluent fractions at the core outlet. Chemical analysis of the effluent samples allows the calculation of an adsorption level based on material balance considerations and also results in a set of effluent profiles for the surfactant and the tracer. In addition to the material balance, adsorption is evaluated by matching experimental effluent concentrations from the core-floods with a convection—dispersion—adsorption numerical model. The model parameters then allow calculation of a complete adsorption isotherm. 

Figure 10. Example of experimental and simulated effluent concentrations from a core-flood and the surfactant adsorption isotherm calculated from the best-fit adsorption model parameters.

Figure 26 also shows the effluent profile of a nonionic surfactant (alkylphenylethoxy alcohol) that was injected into the core containing the preadsorbed anionic surfactant. Material balance calculations indicated that the nonionic surfactant adsorbs as much as it would in a clean core despite the presence of the anionic surfactant on the solid surfaces. The anionic surfactant that was adsorbed during the first two floods is recovered completely. 

The second method used to determine the design mobility is to measure the mobility of the oU/water bank produced by the chemical flood in native-state cores. 131.132 xhe displacement process must produce a stable oil/water bank in a region where the interfacial tension (IFT) is not altered. Fig. 5.90132 presents the results of an oil displacement test in a 4-ft core in which an aqueous surfactant system was injected. A stabilized oil bank formed in the interval where the IFT was not affected by the surfactant. This region is shaded in Fig. 5.90. Total relative mobility was calculated from pressure data for the stabilized oil/water bank with... 

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