Modified Peng-Robinson equation of state for confined fluids: Critical pore size and phase behavior in shale nanopores

作者：Hong-Xian Kuang, Zhouhua Wang, Zhouhua Wang, Na Jia, Hanmin Tu, Yun Li, Huang Liu, Ping Guo, Ziyan Wang, Ziyan Wang · 发表于：Petroleum Science · 年份：2025 · DOI：10.1016/j.petsci.2025.11.010 · 被引用次数：4 · 研究领域：Hydrocarbon exploration and reservoir analysis、Enhanced Oil Recovery Techniques、Phase Equilibria and Thermodynamics

Shale reservoirs are dominated by nanopores, where wall-fluid adsorption and anomalous fluid intermolecular interactions lead to substantial deviations from conventional equation of state (EOS) predictions. This study proposes a modified Peng-Robinson equation of state (m-PR EOS) that incorporates two innovative key corrections: (1) a refined molar volume term accounting for wall-fluid adsorption effects; and (2) introduction of the contact angle in the attractive term to rectify anomalous fluid intermolecular interactions. The m-PR EOS quantitatively captures the shifts in critical properties of confined hydrocarbons and pioneeringly integrates critical pore size determination, identifying confinement thresholds for pure hydrocarbons. The critical pore radii of methane were determined as 18.62 nm (based on temperature shift) and 51.33 nm (based on pressure shift). The analysis reveals that hydrocarbons with larger Lennard-Jones molecular sizes exhibit larger critical pore sizes and greater deviations in critical properties at the same confinement scale. The model validated with binary hydrocarbons was applied to simulate pore-size-dependent phase behavior in shale condensate systems and Constant Composition Expansion experiments. Results demonstrate that reducing pore size causes phase envelope to contract towards the lower-left quadrant in the P-T phase diagram, with accelerated contraction rates. Constant Composition Expansion simulations show that the retrograde condensat...