Flow of nitrogen foam stabilized by alpha olefin sulfonate (C _14-16 AOS) was studied in a natural sandstone porous media using X-ray Computed Tomography. Foam was generated by a simultaneous injection of gas and surfactant solution into a porous medium initially saturated with the surfactant solution. It was found that the foam undergoes a transition from a weak to a strong state at a characteristic gas saturation of S _gc = 0.75 ± 0.02. This transition coincided with a substantial reduction in foam mobility by a two-order of magnitude and also with a large reduction in overall water saturation to as low as 0.10 ± 0.02. Foam mobility transition was interpreted by the surge of yield stress as gas saturation exceeded the S _gc . We proposed a simple power-law functional relationship between yield stress and gas saturation. The proposed rheological model captured successfully the mobility transition of foams stabilized by different surfactant concentrations and for different core lengths.

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The efficiency of alkali-surfactant-polymer (ASP) flooding for enhanced oil recovery (EOR) can be muchless than expected under various reservoir conditions that include low permeability, high temperature,high formation brine salinity and the presence of divalent cations (Ca+2, Mg+2) in the formation brine. Thisis due to polymer degradation and low injectivity, alkali precipitation and scaling in the well and surfaceequipment. Moreover, polymers substantially reduce the capability of treatment of produced water tobe used for re-injection, upcycling or discharge.This paper reports on an experimental study of new chemical EOR approach that has the potential toovercome the above drawbacks. The new chemical formulation consists of the combination of a non-polymeric viscosity enhancement compound and a blend of two surfactants. The performance of thischemical formulation was evaluated by a series of coreflood tests on Bentheimer sandstone cores, understable gravity conditions, with the aid of X-ray Computed Tomography. A significant reduction in theresidual oil saturation was observed by constructing the capillary desaturation curves (CDC), suggestingthat the proposed formulation is potentially a good chemical EOR agent.@en