Immiscible Water Alternating Gas (WAG) projects can be enhanced by using foaming surfactant in the water slugs with the objective to create viscous foam thereby improving the mobility ratio between gas and the liquid phases. The effective dynamic behavior of foam is complex and dependent on many parameters, such as water saturation, oil saturation, surfactant concentration, and capillary number. Besides the WAG design parameters, such as WAG slug size, and WAG ratio, one should also consider how to time and scale the amount of surfactant to be injected, in terms of concentration and slug size. Part of the dynamics of foam behavior has been calibrated in laboratory experiments showing the effective foam strength in foam scans and its dependency on foam quality (With foam quality defined as the gas volumetric flow rate compared to total gas and liquid volumetric flow rate). Nevertheless, small scale experiments have their limitations and uncertainties remain on field scale performance. Deep down in the formation, factors such as foam strength and stability, and adsorption of surfactant are considered uncertain. These factors call for pilots to de-risk the application further. Simulation studies show that foam strength has a major impact on both ultimate recovery as well as surfactant concentration in the produced streams – stronger foam resulting in lower surfactant concentrations.

The injection strategy also has an important impact on recovery. In some cases, recovery efficiency can be impaired if strong foam is created in the immediate wellbore environment, thereby hampering injection and pore-volume throughput. Sustained injectivity during FAWAG is hence an important component to derisk either in pilots, or lab and simulation studies. This paper demonstrates the impact of different injection strategies and offers some suggestions to mitigate the risk of reduced injectivity during FAWAG.

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