Comparability of in situ crude oil emulsification in phase equilibrium and under porous-media-flow conditions.

HYPOTHESIS: The emulsification of water and crude oil is typically examined and optimized in test tubes by optical means, that is, mixed under turbulent conditions and detected outside the porous medium in equilibrium. In this study, we investigate the rather complex case of crude oil emulsification by alkaline solutions to assess whether the classical phase behavior experiments are representative of the emulsification under laminar flow conditions in porous media. EXPERIMENTS: We characterized the phase equilibrium in the test tubes through X-ray attenuation in micro-X-ray computed tomography (µCT). Moreover, we showed that for these systems, the conventional qualitative optical inspection leads to considerable misinterpretation. X-ray attenuation ensures a quantitative analysis directly comparable to results from µCT-based core-flood experiments, where phase mixing occurs in porous media flow. The study was complemented with microfluidic experiments providing additional high-resolution information on emulsion phases. FINDINGS: We conclusively show that in the complex in situ saponification of crude oil by alkaline flooding, (a) the emulsifications in test tubes and in porous media flow are comparable, considering the displacement process in the latter; (b) a minimum emulsion volume with balanced compositions leads to optimal oil recovery in µCT-based and conventional core flooding and in microfluidics.