Mechanisms for CH<sub>4</sub>/CO<sub>2</sub> Swapping in Natural Sediments
Production of natural gas from hydrates involves multiple complex competing phase transitions, which are rarely analyzed thermodynamically. Hydrates in sediments are typically examined in terms of the local conditions of indirect thermodynamic variables, such as temperature and pressure. This can be...
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MDPI AG
2022-07-01
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| Series: | Fluids |
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| Online Access: | https://www.mdpi.com/2311-5521/7/8/260 |
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| author | Bjørn Kvamme |
| author_facet | Bjørn Kvamme |
| author_sort | Bjørn Kvamme |
| collection | DOAJ |
| description | Production of natural gas from hydrates involves multiple complex competing phase transitions, which are rarely analyzed thermodynamically. Hydrates in sediments are typically examined in terms of the local conditions of indirect thermodynamic variables, such as temperature and pressure. This can be very misleading in the evaluation of hydrate production methods. Any hydrate production method is governed by the thermodynamic laws. The combined first and second laws determine phase distributions in terms of Gibbs free energy minimum. This minimum is constrained by the first law of thermodynamics through enthalpy. The entropy changes during a specific action for hydrate production need to be sufficient to overcome the bottlenecks of breaking hydrogen bonds. In this work, I point out some important drawbacks of the pressure reduction method. The main focus is, however, on combined safe long-term storage of CO<sub>2</sub> and release of CH<sub>4</sub>. It is demonstrated that CO<sub>2</sub> hydrate is more stable than CH<sub>4</sub> hydrate, in contrast to interpretations of pressure temperature diagrams, which are frequently used in discussions. Pressure and temperature are independent thermodynamic variables and merely determine at which conditions of these independent variables specific hydrates can exist. Gibbs free energy is the dependent thermodynamic variable that determines the level of phase stability. The first law determines the need for supply of thermodynamic driving forces for hydrate dissociation. Unlike in conventional analysis, it is pointed out that chemical work is also a driving force in the pressure reduction method. The release of heat from the formation of a new CO<sub>2</sub> hydrate from injection gas is the primary source for CH<sub>4</sub> hydrate dissociation in the CO<sub>2</sub> method. Increased salinity due to consumption of pure water for new hydrate could potentially also assist in dissociation of in situ CH<sub>4</sub> hydrate. Based on thermodynamic calculations, it is argued that this effect may not be significant. |
| first_indexed | 2024-03-09T09:57:42Z |
| format | Article |
| id | doaj.art-bbf0683626b64eae8ab8b86d0673244a |
| institution | Directory Open Access Journal |
| issn | 2311-5521 |
| language | English |
| last_indexed | 2024-03-09T09:57:42Z |
| publishDate | 2022-07-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Fluids |
| spelling | doaj.art-bbf0683626b64eae8ab8b86d0673244a2023-12-01T23:42:06ZengMDPI AGFluids2311-55212022-07-017826010.3390/fluids7080260Mechanisms for CH<sub>4</sub>/CO<sub>2</sub> Swapping in Natural SedimentsBjørn Kvamme0State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Xindu Road No. 8, Chengdu 610500, ChinaProduction of natural gas from hydrates involves multiple complex competing phase transitions, which are rarely analyzed thermodynamically. Hydrates in sediments are typically examined in terms of the local conditions of indirect thermodynamic variables, such as temperature and pressure. This can be very misleading in the evaluation of hydrate production methods. Any hydrate production method is governed by the thermodynamic laws. The combined first and second laws determine phase distributions in terms of Gibbs free energy minimum. This minimum is constrained by the first law of thermodynamics through enthalpy. The entropy changes during a specific action for hydrate production need to be sufficient to overcome the bottlenecks of breaking hydrogen bonds. In this work, I point out some important drawbacks of the pressure reduction method. The main focus is, however, on combined safe long-term storage of CO<sub>2</sub> and release of CH<sub>4</sub>. It is demonstrated that CO<sub>2</sub> hydrate is more stable than CH<sub>4</sub> hydrate, in contrast to interpretations of pressure temperature diagrams, which are frequently used in discussions. Pressure and temperature are independent thermodynamic variables and merely determine at which conditions of these independent variables specific hydrates can exist. Gibbs free energy is the dependent thermodynamic variable that determines the level of phase stability. The first law determines the need for supply of thermodynamic driving forces for hydrate dissociation. Unlike in conventional analysis, it is pointed out that chemical work is also a driving force in the pressure reduction method. The release of heat from the formation of a new CO<sub>2</sub> hydrate from injection gas is the primary source for CH<sub>4</sub> hydrate dissociation in the CO<sub>2</sub> method. Increased salinity due to consumption of pure water for new hydrate could potentially also assist in dissociation of in situ CH<sub>4</sub> hydrate. Based on thermodynamic calculations, it is argued that this effect may not be significant.https://www.mdpi.com/2311-5521/7/8/260hydrate swappingnon-equilibriumthermodynamicssaltsmechanisms |
| spellingShingle | Bjørn Kvamme Mechanisms for CH<sub>4</sub>/CO<sub>2</sub> Swapping in Natural Sediments Fluids hydrate swapping non-equilibrium thermodynamics salts mechanisms |
| title | Mechanisms for CH<sub>4</sub>/CO<sub>2</sub> Swapping in Natural Sediments |
| title_full | Mechanisms for CH<sub>4</sub>/CO<sub>2</sub> Swapping in Natural Sediments |
| title_fullStr | Mechanisms for CH<sub>4</sub>/CO<sub>2</sub> Swapping in Natural Sediments |
| title_full_unstemmed | Mechanisms for CH<sub>4</sub>/CO<sub>2</sub> Swapping in Natural Sediments |
| title_short | Mechanisms for CH<sub>4</sub>/CO<sub>2</sub> Swapping in Natural Sediments |
| title_sort | mechanisms for ch sub 4 sub co sub 2 sub swapping in natural sediments |
| topic | hydrate swapping non-equilibrium thermodynamics salts mechanisms |
| url | https://www.mdpi.com/2311-5521/7/8/260 |
| work_keys_str_mv | AT bjørnkvamme mechanismsforchsub4subcosub2subswappinginnaturalsediments |