Molecular dynamics simulation of bubble nucleation and growth during CO2 Huff-n-Puff process in a CO2-heavy oil system

Y Zhang and L Yuan and SZ Liu and JR Zhang and MJ Yang and YC Song, GEOENERGY SCIENCE AND ENGINEERING, 227, 211852 (2023).

DOI: 10.1016/j.geoen.2023.211852

Foamy oil is the main production mechanism in the CO2 Huff-n-Puff process in heavy oil reservoir. However, the micro-formation mechanism of foamy oil in heavy oil recovery is not yet clarified. It is crucial to gain in-depth knowledge about the evolution process of bubbles and its influencing factors to improve the stability of foamy oil. In this work, molecular dynamics simulation (MD) was used to study the microscopic mechanisms of bubble nucleation and growth, and the effect of the depressurization rate on gas evolution in the CO2-heavy oil system. The microscopic process of bubble evolution during depressurization is as follows: CO2 molecules assemble in-side the cavities formed in the oil phase and develop into bubbles, then the bubbles further grow, merge, or disappear. The bubbles evolution is influenced by the binding degree of the surrounding asphaltenes. The macromolecular asphaltene structure contributes to the emergence of cavities in the oil phase for CO2 aggre-gation. The transfer rate of dissolved gas to gas phase increases with time before forming a continuous phase. The potential energy barrier of bubbles is further analyzed to illuminate the morphological mechanism of bubbles in the oil phase. In addition, the bulk phase properties indicate that higher depressurization rates increase the effective pressure range for bubble oil performance. This work reveals the bubble evolution process and the influence of asphaltene, providing molecular-level insights into gas transport and foamy oil stability.

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