Aqueous foams play an important role in many industrial processes, from ore separation by froth flotation to enhanced oil recovery (EOR). In the latter case, the foam is used as a means of increasing the sweep efficiency through the oil bearing rock -the complex, structure dependent, flow behaviour of the foam [Jones et al., 2013] means that it has improved penetration of lower permeability regions than would be obtained with a Newtonian fluid. An understanding of how foam behaves when flowing through a rock is therefore of great importance when selecting suitable surfactants for EOR processes.Previous tests have suggested that there is no reliable correlation between bulk foam behavior and foam behavior in a rock core, especially in the presence of oil [Dalland et al., 1994;Mannhardt et al., 2000]. We present a comparative study of bulk stability tests and core floods with foam, both with and without oil. Core-flood tests were conducted in rock cores with a diameter of 1 cm and length of 17cm, significantly smaller than typical cores [Jones et al, 2015]. Apparent viscosity / injected gas fraction response curves were obtained, both with and without oil in the system. This current work found that there is a positive correlation between bulk foam stability and core flood performance in the absence of oil. Bulk foam experiments can therefore be a useful screening tool to get a good indication of the surfactant performance in the core flood. However, there was no correlation found between bulk foam stability and the performance in the core for the experiments performed in the presence of oil.It is crucial to select the right surfactant, as it stabilizes the foam. The surfactant selection is specific to the application; it depends of the rock chemistry, water salinity, reservoir temperature and the oil type. The general consensus is that the most representative test of the foam behavior, especially in presence of oil, is the coreflood experiment at the reservoir conditions. However coreflood tests are timedemanding and expensive so that only a limited number of surfactants can be tested. Bulk foam tests

We present an insightful discussion on the implications of foam transport inside porous media based on an improved algorithm for the estimation of model parameters. A widely used texture-implicit local-equilibrium foam model, STARS TM , is used to describe the reduction of gas mobility in the state of foam with respect to free gas. Both the dry-out effect and sheardependent rheology are considered in foam simulations. We estimate the limiting capillary pressure ! * from values in the STARS TM model to characterize foam film stability in a dynamic flowing system. We find that ! * is a good indicator of foam strength in porous media and varies with different gas types. We also calculate ! * for different foaming surfactants and find that foam stability is correlated with the Gibbs surface excess concentration. We compare our improved parameter estimation algorithm with others reported in literature. The robustness of the algorithm is validated for various foam systems.

Foam can be used for gas mobility control in different subsurface applications. The success of foam-injection process depends on foam-generation and propagation rate inside the porous medium. In some cases, foam properties depend on the history of the flow or concentration of the surfactant, i.e., the hysteresis effect. Foam may show hysteresis behavior by exhibiting multiple states at the same injection conditions, where coarse-textured foam is converted into strong foam with fine texture at a critical injection velocity or pressure gradient. This study aims to investigate the effects of injection velocity and surfactant concentration on foam generation and hysteresis behavior as a function of foam quality. We find that the transition from coarse-foam to strong-foam (i.e., the minimum pressure gradient for foam generation) is almost independent of flowrate, surfactant concentration, and foam quality. Moreover, the hysteresis behavior in foam generation occurs only at high-quality regimes and when the pressure gradient is below a certain value regardless of the total flow rate and surfactant concentration. We also observe that the rheological behavior of foam is strongly dependent on liquid velocity.

We present the results of an experimental investigation of the effect of gas type and composition on foam transport in porous media. Steady-state foam strengths with respect to three cases of distinct gases and two cases containing binary mixtures of these gases were compared. The effects of gas solubility, the stability of lamellae, and the gas diffusion rate across the lamellae were examined. Our experimental results showed that the steady-state foam strength is inversely correlated with the gas permeability across a liquid lamella, a parameter that characterizes the rate of mass transport. The results are also in good agreement with existing observations that the foam strength for a mixture of gases is correlated with the less soluble component. Three hypotheses with different predictions of the underlying mechanism that explain the role of gas type and composition in foam strength are discussed in detail.