Investigation into the effects of CO2 and CH4 dissolution on crude oil viscosity and the relevant viscosity reduction mechanism
Abstract
To improve gas-assisted oil recovery, it is crucial to understand how dissolved gases influence crude-oil viscosity. However, the molecular mechanisms linking gas uptake to changes in rheological behavior remain unclear. This study aims to investigate the effects of temperature, pressure and gas composition on this process by combining grand canonical Monte Carlo simulations, molecular dynamics simulations, and quantum chemical calculations. Gas uptake, rheological behavior, intermolecular interactions, accessible free volume, volumetric expansion, molecular conformation, and mobility are examined. It is found that gas uptake increases with pressure but decreases with temperature. Carbon dioxide exhibits greater uptake than methane under comparable conditions. All gas-containing systems show shear thinning behavior. Increasing the carbon dioxide fraction generally reduces apparent viscosity at low shear rates, while differences among the systems become smaller at higher shear rates. Molecular analysis suggests that dissolved gases weaken associations between resins and asphaltenes, leading to a less connected heavy-fraction network. Probe-based analysis reveals that carbon dioxide can access more of the existing microscopic void space than methane. Systems enriched with carbon dioxide also exhibit greater volumetric expansion and enhanced molecular mobility, whereas conformational changes in resins and asphaltenes remain limited. These findings suggest that viscosity reduction involves preferential carbon dioxide uptake, weakened heavy-fraction associations, volumetric expansion, as well as increased molecular mobility. The results provide a molecular basis for understanding gas-induced viscosity reduction and may guide gas composition selection during crude-oil recovery.
Document Type: Original article
Cited as: Li, B., Wu, S., Chen, L., Han, J., Zhu, H. Investigation into the effects of CO2 and CH4 dissolution on crude oil viscosity and the relevant viscosity reduction mechanism. Advances in Geo-Energy Research, 2026, 22(1): 72-86. https://doi.org/10.46690/ager.2026.10.06
DOI:
https://doi.org/10.46690/ager.2026.10.06Keywords:
CO2/CH4, rheological mechanisms, molecular dynamics simulations, viscosity reductionReferences
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Copyright (c) 2026 Bingfan Li, Shijun Wu, Lei Chen, Jiang Han, Hongjian Zhu
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