Diffusion of N 2 /CH 4 /CO 2 in Heptane-Containing Nanoblind Ends

Yiran Wang, Xinglong Chen (), Nannan Liu and Hengchen Qi
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Yiran Wang: School of Engineering Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
Xinglong Chen: School of Engineering Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
Nannan Liu: School of Petroleum and Natural Gas Engineering, Changzhou University, Changzhou 213164, China
Hengchen Qi: School of Petroleum and Natural Gas Engineering, Changzhou University, Changzhou 213164, China

Energies, 2024, vol. 17, issue 21, 1-19

Abstract: The prevalence of micropores and nanopores in low-permeability reservoirs is a cause for concern, as it results in a sizeable quantity of oil reserves being trapped within them. The water-gas dispersion system has the capacity to expand the reservoirs’ wave volume and enhance oil recovery. While the microscopic oil repulsion mechanism has been the center of attention, the oil repulsion effect of three distinct types of gases (N 2 , CH 4 , and CO 2 ) is of particular importance in understanding the displacement mechanism of N 2 /CH 4 /CO 2 on heptane at the blind end of the nanometer. A molecular dynamics simulation using the LAMMPS software was employed to construct a model of a blind end of heptane on a SiO 2 wall and an interface model with different types of gas molecules. This was done to investigate the microscopic mechanism of heptane replacement by gas molecules. The temperature (50 °C) and pressure (30 MPa) of the reservoir in the Changqing oil field are selected as the parameters for analysis. The findings indicate that all three types of gas molecules can enter the blind end and displace heptane. However, supercritical CO 2 forms a mixed phase with heptane, which is more prone to extruding oil molecules situated near the inner wall surface of the blind end and desorbing the oil film. The results demonstrate that, in the context of the blind end, gaseous CO 2 exhibits a lower solvation ability but superior extrusion diffusion ability for heptane compared to N 2 and CH 4 . Furthermore, the interaction energy indicates that the interactions between two states of CO 2 and heptane, as well as the thickness of the interface, increase with increasing pressure and temperature. The findings of this study elucidate the microscopic mechanism underlying the replacement of oil droplets or oil films at the blind end by different gases under reservoir conditions at the molecular level and offer further guidance for the selection of the gas phase and the replacement state in the water-gas dispersive drive system.

Keywords: gas molecules; heptane; blind-end model; oil drive mechanism; molecular dynamics simulation (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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