Pore-scale events in drainage process through porous media under high- and low-interfacial tension flow conditions

Abstract

In spite of the available literature on the evaluation of the drainage under the high- and low-interfacial tension (IFT) flow through porous media, distribution and the detailed topology and structure of the displacing non-wetting and the trapped wetting phases at the pore level, and some of the pore-scale phenomena have not been understood in a comprehensive manner. The aim of this study is to provide insight into the above-mentioned issues in a preferentially oil-wet porous medium partially filled with the heavy oil and connate water, which is flooded with the brine (simulating secondary drainage or high-IFT waterflooding) and with the surfactant solution (simulating tertiary drainage or low-IFT surfactant-enhanced waterflooding). This paper consists of two parts. The first part provides a detailed, comprehensive literature survey of the recent advances in the experimental study and modeling of the drainage process in porous media. In the second part, the authors present their experimental observations of the pore-level events and the displacement front configurations of drainage under the high- and low-IFT flow conditions in a one-quarter five-spot, etched glass micromodel. First, distribution, configuration, and topology of the trapped air in primary drainage (i.e., air displacement by brine or connate water) are depicted. Second, the detailed pore-scale topology, structure, distribution, and configuration of the displaced and displacing phases in primary imbibition (i.e., desaturation of the continuous non-wetting phase, or wetting process, which occurs during the displacement of brine in a preferentially oil-wet porous medium by heavy oil), secondary drainage (i.e., desaturation of the continuous wetting phase under the high-IFT flow condition, which occurs during the high-IFT waterflooding in a preferentially oil-wet porous medium), and tertiary drainage (i.e., mobilization of the discontinuous trapped wetting phase under the low-IFT flow condition, which occurs during the low-IFT surfactant-enhanced waterflooding in a preferentially oil-wet porous medium), are elucidated in detail. Third, the major pore-scale displacement phenomena in tertiary drainage under the low-IFT flow conditions are explained. Furthermore, the advance of the displacement front and the flow pattern configuration in the secondary and tertiary drainage are analyzed. Finally, the displacing non-wetting phase blob size distribution in the tertiary drainage is presented together with the values of the desaturated fraction of different phases at different stages of the displacement.