Mutual interactions between crude oil and CO 2 under different pressures

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In this paper, the mutual interactions between a crude oil and CO 2 under different pressures and their effects on the crude oil–CO 2 interfacial tension (IFT) and the CO 2 enhanced oil recovery (EOR) are experimentally studied. Firstly, a series of crude oil–CO 2 saturation tests is conducted under different equilibrium pressures in a visual high-pressure saturation cell to determine the onset pressure of the asphaltene precipitation for the crude oil–CO 2 system. Secondly, the axisymmetric drop shape analysis (ADSA) technique for the pendant drop case is applied to measure the equilibrium IFT between the crude oil and CO 2 as a function of the equilibrium pressure at T = 27 °C. The major component of the ADSA system is a see-through windowed high-pressure cell, which makes it possible to visualize the interfacial interactions between the crude oil and CO 2 under the practical reservoir conditions. It is found that the measured crude oil–CO 2 equilibrium IFT is reduced almost linearly with the equilibrium pressure, as long as it is lower than a threshold pressure. It is observed that if the equilibrium pressure is high enough, the light components in the original crude oil are quickly extracted from the oil drop to CO 2 phase at the beginning. This physical phenomenon is referred to as the initial strong light-components extraction. The onset pressure of the initial strong light-components extraction is found to be higher than that of the asphaltene precipitation for the crude oil–CO 2 system determined in the saturation tests. Thirdly, a series of CO 2 coreflood tests is performed to study the effect of the mutual interactions between the crude oil and CO 2 under different CO 2 injection pressures on the CO 2 EOR. The detailed CO 2 coreflood test results show that the CO 2 EOR is increased sharply with the CO 2 injection pressure only if it is in an intermediate range.