Mechanism of heavy alkane influence on CO2 and CH4 competitive adsorption in shale
In shale gas reservoirs, CH4 often coexists with heavy alkanes such as C2H6 and C3H8. To investigate the mechanism by which heavy alkanes affect the competitive adsorption of CH4 and CO2 in organic nanopores of shale, this study combines density functional theory and Grand Canonical Monte Carlo simu...
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| Format: | Article |
| Language: | zho |
| Published: |
Editorial Department of Petroleum Reservoir Evaluation and Development
2025-08-01
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| Series: | Youqicang pingjia yu kaifa |
| Subjects: | |
| Online Access: | https://red.magtech.org.cn/fileup/2095-1426/PDF/1752895828409-2076606753.pdf |
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| Summary: | In shale gas reservoirs, CH4 often coexists with heavy alkanes such as C2H6 and C3H8. To investigate the mechanism by which heavy alkanes affect the competitive adsorption of CH4 and CO2 in organic nanopores of shale, this study combines density functional theory and Grand Canonical Monte Carlo simulations. The interaction types and strengths between gas molecules and kerogen were systematically analyzed in terms of adsorption energy, structural characteristics, weak interaction analysis, and isothermal adsorption. The adsorption performance of pure-component gases was examined, followed by an evaluation of the influence of varying C2H6 and C3H8 concentrations on CH4 adsorption performance. Furthermore, the influence of C2H6 and C3H8 on CO2 and CH4 competitive adsorption was analyzed. The results showed that: (1) With the elongation of alkane carbon chains, the interaction strength between gas molecules and kerogen progressively intensified. The adsorption energies of the four gas molecules on the kerogen surface followed the order: C3H8>C2H6>CO2>CH4. (2) For single-component gas adsorption, the total adsorption capacity decreased from CH4 to C3H8 due to the increased adsorption sites occupied by individual alkanes. Meanwhile, CO2 exhibited a higher adsorption capacity, which was attributed to its unique geometric structure. (3) With rising system temperature, the adsorption capacity of various gas molecules declined. As system pressure increased, the incremental rise in gas adsorption capacity gradually diminished. (4) In binary mixture adsorption, the existence of C2H6 and C3H8 significantly reduced the CH4 adsorption capacity, with C3H8 exhibiting a more significant effect. Meanwhile, the addition of CO2 greatly decreased CH4 adsorption capacity. (5) In ternary mixture adsorption, the coexistence of C2H6, C3H8, and CO2 demonstrated a synergistic effect on promoting CH4 desorption. Specifically, the most effective promotion of CH4 production was achieved when C2H6 and C3H8 accounted for 4% and 8% of the total gas mixture by mass. In addition, compared with C3H8, C2H6 was more favorable to the storage of CO2. These findings provide theoretical support for multicomponent competitive adsorption in shale gas and for CO2-enhanced shale gas extraction. |
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| ISSN: | 2095-1426 |