Surfactant propagation

In addition to the mobihty control characteristics of surfactants, critical issues in gas mobihty control processes are surfactant salinity tolerance, hydrolytic stabihty under reservoir conditions, surfactant propagation through the reservoir, and foam stabihty in the presence of cmde oil saturations. 

The effect of temperature, pressure, and oil composition on oil recovery efficiency have all been the subjects of intensive study (241). Surfactant propagation is a critical factor in determining the EOR process economics (242). Surfactant retention owing to partitioning into residual cmde oil can be significant compared to adsorption and reduce surfactant propagation rate appreciably (243). 

Surfactant propagation experiments. These determine the surfactant propagation rate in a sandpack in the absence of a vapor phase at temperatures from 212-350°F. 

The critical micellar concentrations of anionic/nonionic surfactant mixtures examined are low in a saline medium, so that, at the concentrations injected in practice, the chromatographic effects resulting from the respective adsorption of monomers are masked. Such surfactants propagate simultaneously in the medium in the form of mixed micelles. 

Surfactant-polymer flooding, 13 628 Surfactant precipitation, in volumetric sweep efficiency, 13 621 Surfactant propagation, in enhanced oil recovery, 13 629... 

Surfactant propagation in the reservoirs has been modeled (44, 45) by allowing for surfactant adsorption, oil partitioning, and first-order surfactant decomposition all of these variables are functions of temperature. The foam mobility reduction is taken into account by reducing the gas relative permeability as follows ... 

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... 

Table I shows some statistics on the types of reservoir subjected to enhanced recovery operations. Most EOR projects in Canada, particularly hydrocarbon-miscible projects, are being conducted in carbonate reservoirs, and hydrocarbon injection in the United States is mostly in sandstones. As will be evident from this chapter, the type of reservoir rock is of significance to surfactant propagation during foam-flooding.

Surfactant Adsorption. Surfactant propagation is crucial to foam propagation. The data compiled in later sections of this chapter show that surfactants that are similarly effective as gas mobility reducing agents may have significant differences in adsorption levels. The level of surfactant adsorption and its dependence on parameters such as brine salinity and hardness may then be the deciding factors in surfactant selection for a specific application. 

Figure 7 shows how the measured adsorption levels translate into distance of surfactant propagation in a homogeneous reservoir with radial flow from the injector. A 40-acre five-spot pattern was assumed in calculating the pore volume (PV), and other assumptions are listed in the figure. The calculation of radial distance is based on a simple material balance using the following equation ... 

Figure 7. Example of radial surfactant propagation in a homogeneous reservoir.

The experimental data in Figure 6 indicate that many surfactant systems allow for sufficient surfactant propagation even at high-salinity conditions, but clearly, the proper choice of surfactant is essential for a successful foam-flood. The following sections outline some surfactant systems suitable for foam-flooding at high salinity, and give a detailed review of the adsorption properties of these surfactants. 

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