The flow of nitrogen foam in Bentheimer sandstone cores previously saturated with a surfactant solution has been investigated experimentally. The displacement process was visualized with the aid of a CT scanner. The CT data were analyzed to obtain water saturation profiles at different times. The pressure drops measured over core segments were recorded to determine the foam mobility. It was found that foam undergoes a transition from a weak to a strong state at critical gas saturation of Sgc = 0.75±0.02. This effect could be interpreted successfully in terms of the surge of the yield stress of the foam at this value. It is suggested that a confined jamming is most likely responsible for the mobility transition.

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