Chen Feiyu, Sun Linghui, Li Bowen, Pan Xiuxiu, Jiang Boyu, Huo Xu, Zhang Zhirong, Feng Chun
University of Chinese Academy of Sciences, Beijing 100049, China.
Institute of Porous Flow and Fluid Mechanics, Chinese Academy of Sciences, Langfang 065007, China.
Molecules. 2025 Jan 12;30(2):277. doi: 10.3390/molecules30020277.
CO flooding plays a crucial role in enhancing oil recovery and achieving carbon reduction targets, particularly in unconventional reservoirs with complex pore structures. The phase behavior of CO and hydrocarbons at different scales significantly affects oil recovery efficiency, yet its underlying mechanisms remain insufficiently understood. This study improves existing thermodynamic models by introducing Helmholtz free energy as a convergence criterion and incorporating adsorption effects in micro- and nano-scale pores. This study refines existing thermodynamic models by incorporating Helmholtz free energy as a convergence criterion, offering a more accurate representation of confined phase behavior. Unlike conventional Gibbs free energy-based models, this approach effectively accounts for confinement-induced deviations in phase equilibrium, ensuring improved predictive accuracy for nanoscale reservoirs. Additionally, adsorption effects in micro- and nano-scale pores are explicitly integrated to enhance model reliability. A multi-scale thermodynamic model for CO-hydrocarbon systems is developed and validated through physical simulations. Key findings indicate that as the scale decreases from bulk to 10 nm, the bubble point pressure shows a deviation of 5% to 23%, while the density of confined fluids increases by approximately 2%. The results also reveal that smaller pores restrict gas expansion, leading to an enhanced CO solubility effect and stronger phase mixing behavior. Through phase diagram analysis, density expansion, multi-stage contact, and differential separation simulations, we further clarify how confinement influences CO injection efficiency. These findings provide new insights into phase behavior changes in confined porous media, improving the accuracy of CO flooding predictions. The proposed model offers a more precise framework for evaluating phase transitions in unconventional reservoirs, aiding in the optimization of CO-based enhanced oil recovery strategies.
CO驱替在提高原油采收率和实现碳减排目标方面发挥着关键作用，特别是在具有复杂孔隙结构的非常规油藏中。CO与烃类在不同尺度下的相行为显著影响原油采收效率，但其潜在机制仍未得到充分理解。本研究通过引入亥姆霍兹自由能作为收敛准则，并将吸附效应纳入微米和纳米尺度孔隙中，改进了现有的热力学模型。本研究通过将亥姆霍兹自由能作为收敛准则来完善现有的热力学模型，从而更准确地描述受限相行为。与传统的基于吉布斯自由能的模型不同，这种方法有效地考虑了受限引起的相平衡偏差，确保了对纳米尺度油藏预测精度的提高。此外，明确整合了微米和纳米尺度孔隙中的吸附效应，以提高模型的可靠性。开发了一种用于CO-烃系统的多尺度热力学模型，并通过物理模拟进行了验证。关键研究结果表明，随着尺度从宏观降至10nm，泡点压力显示出5%至23%的偏差，而受限流体的密度增加了约2%。结果还表明，较小的孔隙会限制气体膨胀，导致CO溶解效应增强和相混合行为更强。通过相图分析、密度膨胀、多级接触和微分分离模拟，我们进一步阐明了受限如何影响CO注入效率。这些发现为受限多孔介质中的相行为变化提供了新的见解，提高了CO驱替预测的准确性。所提出的模型为评估非常规油藏中的相变提供了一个更精确的框架，有助于优化基于CO的强化采油策略。
