Representing slow foam dynamics in laboratory corefloods for enhanced oil recovery

On thelaboratory scale, foam can be slow to come to steady state (local equilibrium). In fitting dynamic foam corefloods, if local equilibrium does not apply, it is essential to understand and fit the dynamics so that an accurate local-equilibrium model can be applied on the field scale. We report an attempt to represent slow foam dynamics using a simple first-order kinetic expression for the approach of foam to steady state in a population-balance model. In particular, we attempt to fit a case of gas injection into a surfactant-saturated core ("SAG" injection) (Ma et al., 2013), where the peak in pressure difference across the core takes place well after gas breakthrough, in violation of most local-equilibrium foam models. As the kinetics of foam generation are slowed in our model, the peak pressure gradient is reduced, but the timing of the peak remains at the time of gas breakthrough, i.e. after less than one pore volume injection. For sufficiently slow kinetics, the peak can be broadened significantly by spreading of the traveling wave at the shock at the foam front. We survey published population-balance models for mechanisms that could give a late peak in pressure gradient in a SAG coreflood. Most previous studies with population-balance models use parameter values that would give rapid foam generation and a peak in pressure drop at gas breakthrough in a SAG coreflood. The data of Ma et al. suggest an abrupt onset of foam generation later in the coreflood. to represent it, we believe some sort of triggering mechanism for foam generation (for instance, pressure gradient) is needed in the population-balance model. Another possible mechanism leading to a late peak is a nonlinear response of gas relative permeability to gas trapping and refining foam texture. Copyright 2014, Society of Petroleum Engineers