Insights into Effects of Surfactant Concentration on Foam Behavior in Porous Media

A potential solution to mitigate the adverse effects of viscous fingering, gravity override, and reservoir heterogeneity on the efficiency of gas injection in porous media is to inject the gas with a solution containing surface-active agents such as surfactants or nanoparticles. The efficiency of these processes largely depends on the generation and stability of the lamellae residing in the pores, both of which are influenced by the physicochemical properties of the rock and surfactant solution. In this study, the effect of surfactant concentration on the transient and steady-state foam behavior in porous media was investigated. Several core flood experiments were conducted, in which the nitrogen gas and surfactant solutions with different concentrations were simultaneously injected into a Bentheimer sandstone core. Moreover, the ability of the current foam models in simulating the effect of surfactant concentration was examined and modifications were suggested accordingly. For the cases investigated and under our experimental conditions, the following conclusions are made: • Strong foams can be generated with a very low surfactant concentration in the low-quality regime, albeit with a very slow generation rate. • Surfactant concentration has a significant influence on the transient foam behavior or foam generation. The rate of foam generation increases with the increase of the surfactant concentration. • The transition from coarse to strong foam occurs earlier as the surfactant concentration increases. • Surfactant concentration does not impact the steady-state behavior of foam in the low-quality regime. • In the high-quality regime, the foam strength increases with increasing surfactant concentration. This is attributed to the influence of the limiting capillary on foam stability in this regime, whose value increases with the increase in surfactant concentration. • The current formulation of the steady-state implicit-textured foam models is unable to model the effect of the surfactant concentration, because the current model scales both high- and low-quality regimes with the surfactant concentration. The only surfactant dependent parameter in IT foam models is the limiting water saturation or the fmdry parameter. Therefore, the effect of the surfactant concentration can be reflected solely by the fmdry parameter and there is no need for a separate surfactant-concentration function. © 2019 European Association of Geoscientists and Engineers, EAGE. All Rights Reserved.