Bubble-Point Pressure Deviations and Metastable Nucleation in Nanoconfined CO2–Shale Oil Systems: Effects of Temperature, Composition, Gas–Oil Ratio, and Pore-Scale Coupling
- 1Daqing Oilfield of China National Petroleum Cooperation, Daqing 163700, China
- 2State Key Laboratory of Continental Shale Oil, Daqing 163712, China
- 3State Key Laboratory of Deep Oil and Gas, School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China
Abstract
Bubble-point behavior of shale oil under nanoconfinement is critical for understanding phase evolution during CO2-enhanced shale-oil recovery. In this study, visual micro/nanofluidic PVT experiments were conducted to systematically investigate bubble-point pressure deviations of pentane–CO2, hexadecane–CO2, pentane/decane/hexadecane–CO2, and shale oil–CO2 systems. Measurements were performed at gas–oil ratios of 130 and 260 and temperatures of 65–125 °C using a 10 nm single-scale pore model and a coupled 10 μm–10 nm pore-network model. Experimental results were compared with theoretical predictions from a confinement-modified Peng–Robinson equation of state incorporating capillary pressure, surface adsorption, and critical-property shifts. Furthermore, a metastable nucleation limit was introduced to describe the experimentally observed phase-transition pressure below the equilibrium bubble-point boundary. Pronounced downward deviations toward the metastable region were observed in isolated 10 nm pores. For the pentane–CO2 system at 65 °C and GOR = 130, the experimentally observed phase-transition pressure was approximately 3.5 MPa, compared with an equilibrium prediction of 4.3 MPa, corresponding to a relative deviation of 18.35%. The deviation decreased as temperature approached the critical region and was reduced at higher GOR. For example, at GOR = 260, the deviation of the hexadecane–CO2 system decreased from 40.63% at 65 °C to 10.01% at 125 °C. Fluid composition also strongly affected confinement sensitivity, with heavier hydrocarbon systems exhibiting stronger shifts toward metastable behavior. In contrast, bubble-point pressures in the coupled 10 μm–10 nm network remained close to the equilibrium predictions of the micrometer-scale pores and deviated significantly from the metastable limit. For the shale oil–CO2 system at 65 °C and GOR = 130, the relative deviation decreased from 29.77% in the isolated 10 nm pore model to only 2.43% in the coupled 10 μm–10 nm network. These results demonstrate that nanoconfined bubble-point behavior is governed by the coupled effects of thermodynamic conditions, fluid composition, metastability, and pore-scale connectivity.
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BibTeX
@article{qi2026bubblepoint,
title = {{Bubble-Point Pressure Deviations and Metastable Nucleation in Nanoconfined CO2–Shale Oil Systems: Effects of Temperature, Composition, Gas–Oil Ratio, and Pore-Scale Coupling}},
author = {Dongyan Qi and Jiawei Li and Qiang Liu and Shuang Wang and Siyuan Cui and Yue Lang and Jiayi Zhao and Xiaozhe Liang and Junjie Zhong},
journal = {Nanomaterials (Basel, Switzerland)},
year = {2026},
month = oct,
doi = {10.3390/nano16191260},
url = {https://europepmc.org/article/PMC/PMC13667126},
note = {CC BY},
}
RIS
TY - JOUR
TI - Bubble-Point Pressure Deviations and Metastable Nucleation in Nanoconfined CO2–Shale Oil Systems: Effects of Temperature, Composition, Gas–Oil Ratio, and Pore-Scale Coupling
AU - Dongyan Qi
AU - Jiawei Li
AU - Qiang Liu
AU - Shuang Wang
AU - Siyuan Cui
AU - Yue Lang
AU - Jiayi Zhao
AU - Xiaozhe Liang
AU - Junjie Zhong
PY - 2026
DA - 2026/10/01
JO - Nanomaterials (Basel, Switzerland)
DO - 10.3390/nano16191260
UR - https://europepmc.org/article/PMC/PMC13667126
AB - Bubble-point behavior of shale oil under nanoconfinement is critical for understanding phase evolution during CO2-enhanced shale-oil recovery. In this study, visual micro/nanofluidic PVT experiments were conducted to systematically investigate bubble-point pressure deviations of pentane–CO2, hexadecane–CO2, pentane/decane/hexadecane–CO2, and shale oil–CO2 systems. Measurements were performed at gas–oil ratios of 130 and 260 and temperatures of 65–125 °C using a 10 nm single-scale pore model and a coupled 10 μm–10 nm pore-network model. Experimental results were compared with theoretical predictions from a confinement-modified Peng–Robinson equation of state incorporating capillary pressure, surface adsorption, and critical-property shifts. Furthermore, a metastable nucleation limit was introduced to describe the experimentally observed phase-transition pressure below the equilibrium bubble-point boundary. Pronounced downward deviations toward the metastable region were observed in isolated 10 nm pores. For the pentane–CO2 system at 65 °C and GOR = 130, the experimentally observed phase-transition pressure was approximately 3.5 MPa, compared with an equilibrium prediction of 4.3 MPa, corresponding to a relative deviation of 18.35%. The deviation decreased as temperature approached the critical region and was reduced at higher GOR. For example, at GOR = 260, the deviation of the hexadecane–CO2 system decreased from 40.63% at 65 °C to 10.01% at 125 °C. Fluid composition also strongly affected confinement sensitivity, with heavier hydrocarbon systems exhibiting stronger shifts toward metastable behavior. In contrast, bubble-point pressures in the coupled 10 μm–10 nm network remained close to the equilibrium predictions of the micrometer-scale pores and deviated significantly from the metastable limit. For the shale oil–CO2 system at 65 °C and GOR = 130, the relative deviation decreased from 29.77% in the isolated 10 nm pore model to only 2.43% in the coupled 10 μm–10 nm network. These results demonstrate that nanoconfined bubble-point behavior is governed by the coupled effects of thermodynamic conditions, fluid composition, metastability, and pore-scale connectivity.
SN - 2079-4991
ER -