Mechanism of alcohols enhancing CO2-oil miscibility for carbon storage and enhanced oil recovery: Molecular insights

SY Liu and JY Chen and MF Li and J Zhong and JR Liu and WY Sun, GEOENERGY SCIENCE AND ENGINEERING, 250, 213837 (2025).

DOI: 10.1016/j.geoen.2025.213837

Carbon capture utilization and storage (CCUS) is considered one of the most promising approaches for carbon neutrality. Thereinto, it is more realistic and feasible to inject CO2 into hydrocarbon reservoirs for geological storage and simultaneously enhanced oil recovery (CO2-EOR). CO2 miscible flooding is far superior to immiscible flooding in storing more CO2 and producing more oil, but some reservoirs face the challenge of miscible flooding due to a high minimum miscibility pressure (MMP). Facing this issue, this work analyzes the impact of straightchain (ethanol, pentanol) and branched-chain alcohols (2-pentanol) on the CO2-oil MMP by employing molecular dynamics simulation for revealing the mechanism of different types of alcohol additives enhancing the CO2-oil miscibility from the molecular aspects of interaction energies, and radial distribution function (RDF). Results indicate that the studied alcohols can significantly lower the CO2-oil MMP due to the 'amphipathicity' characteristic of oil-philicity and CO2-philicity. Ethanol has the best effect to enhance miscibility. The molecular structure of alcohols plays a key role in reducing MMP, and straight- chain alcohols are more effective in aggregating CO2 around their hydroxyl groups, compared to branched-chain alcohols. The hydroxyl groups of straight-chain alcohols are less hindered by spatial constraints, showing stronger affinities with CO2, thereby more effectively disrupting the cohesion within the oil phase and reducing MMP. The findings of this work provide some new insights into achieving miscible CO2 flooding and offer guidance on employing suitable alcohol additives to improve the effect of CO2-EOR.

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