A mechanistic foam modeling technique based on bubble population balance, which honors three different foam states (weak-foam, strong-foam, and intermediate states) and two steady-state strong-foam flow regimes (high-quality regime and low-quality regime of the strong-foam state), is developed to investigate how CO2 foam behaves rheologically and propagates in a petroleum reservoir. The model parameters are first obtained from a fit to existing laboratory coreflood experimental data, and then the mechanistic model is applied to different types of CO2 foams, ranging from gaseous to supercritical CO2 foams, represented by various mobilization pressure gradients.
The results from the fit to existing coreflood data show that a reasonable match can be made satisfying multiple constraints such as hysteresis exerted by three foam states, non-Newtonian flow behavior caused by gas trapping and shear thinning rheology, and bubble stability at different capillary pressure environments. Among different sets of input parameters resulting in equally nice fits, an additional experimental data (for example, the onset of foam generation by increasing the total flow rate step by step at fixed foam quality) can help narrow down the range of input parameters further. When applied to field-scale scenarios, supercritical CO2 foams requiring low mobilization pressure gradient propagate much further than gaseous CO2 foams, far enough to make use of supercritical CO2 foams promising in the fields. This in turn proves theoretically why supercritical CO2 foams should be preferred in the field compared to gaseous CO2 foams. The model shows foams in the low-quality regime can propagate longer distance than foams in the high-quality regime because of better foam stability at lower capillary pressure environment.