Effect of Methane Cracking on Carbon Isotope Reversal and the Production of Over-Mature Shale Gas
The geochemical statistics indicate that the wetness (C<sub>2</sub>~C<sub>5</sub>/C<sub>1</sub>~C<sub>5</sub>) of over-mature shale gas with carbon isotope reversal is less than 1.8%. The magnitude of carbon isotope reversal (δ<sup>13</sup>...
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MDPI AG
2022-08-01
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| Series: | Energies |
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| Online Access: | https://www.mdpi.com/1996-1073/15/17/6285 |
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| author | Jingkui Mi Wei Wu Di Zhu Ziqi Feng |
| author_facet | Jingkui Mi Wei Wu Di Zhu Ziqi Feng |
| author_sort | Jingkui Mi |
| collection | DOAJ |
| description | The geochemical statistics indicate that the wetness (C<sub>2</sub>~C<sub>5</sub>/C<sub>1</sub>~C<sub>5</sub>) of over-mature shale gas with carbon isotope reversal is less than 1.8%. The magnitude of carbon isotope reversal (δ<sup>13</sup>C<sub>1</sub>–δ<sup>13</sup>C<sub>2</sub>) increases with decreasing wetness within a wetness range of 0.9~1.8% and then decreases at wetness <0.9%. The experimental result demonstrates that CH<sub>4</sub> polymerization proceeding to CH<sub>4</sub> substantial cracking is an important factor involved in isotope reversal of over-mature shale gas. Moreover, δ<sup>13</sup>C<sub>1</sub>–δ<sup>13</sup>C<sub>2</sub> decreases with an increase in experimental temperature prior to CH<sub>4</sub> substantial cracking. The values of δ<sup>13</sup>C<sub>1</sub> and δ<sup>13</sup>C<sub>2</sub> tend to equalize during CH<sub>4</sub> substantial cracking. The δ<sup>13</sup>C<sub>1</sub>–δ<sup>13</sup>C<sub>2</sub> of mud gas investigated at different depths during shale gas drilling in the Sichuan Basin increases initially, then decreases with further increase in the depth, and finally tends to zero, with only a trace hydrocarbon gas being detectable. Thus, the approximately equal value between δ<sup>13</sup>C<sub>1</sub> and δ<sup>13</sup>C<sub>2</sub> for over-mature shale gas and very low wetness could potentially serve as useful criteria to screen CH<sub>4</sub> substantial cracking. Two geochemical indices to indicate CH<sub>4</sub> substantial cracking in a geological setting are proposed according to the variation production data with the geochemistry of over-mature shale gas in the Sichuan Basin, China. |
| first_indexed | 2024-03-10T01:51:56Z |
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| id | doaj.art-6145fea7f9424f4eb92e02c3c060ab86 |
| institution | Directory Open Access Journal |
| issn | 1996-1073 |
| language | English |
| last_indexed | 2024-03-10T01:51:56Z |
| publishDate | 2022-08-01 |
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| series | Energies |
| spelling | doaj.art-6145fea7f9424f4eb92e02c3c060ab862023-11-23T13:03:33ZengMDPI AGEnergies1996-10732022-08-011517628510.3390/en15176285Effect of Methane Cracking on Carbon Isotope Reversal and the Production of Over-Mature Shale GasJingkui Mi0Wei Wu1Di Zhu2Ziqi Feng3State Key Laboratory for Enhanced Oil Recovery, Beijing 100083, ChinaExploration and Development Research Institute, PetroChina Southwest Oil and Gas Field Company, Chengdu 610041, ChinaKey Laboratory for Biomass Gasification Technology of Shandong Province, Energy Research Institute, Jinan 250014, ChinaSchool of Geosciences and Key Laboratory of Deep Oil and Gas, China University of Petroleum (Shandong), Qingdao 266580, ChinaThe geochemical statistics indicate that the wetness (C<sub>2</sub>~C<sub>5</sub>/C<sub>1</sub>~C<sub>5</sub>) of over-mature shale gas with carbon isotope reversal is less than 1.8%. The magnitude of carbon isotope reversal (δ<sup>13</sup>C<sub>1</sub>–δ<sup>13</sup>C<sub>2</sub>) increases with decreasing wetness within a wetness range of 0.9~1.8% and then decreases at wetness <0.9%. The experimental result demonstrates that CH<sub>4</sub> polymerization proceeding to CH<sub>4</sub> substantial cracking is an important factor involved in isotope reversal of over-mature shale gas. Moreover, δ<sup>13</sup>C<sub>1</sub>–δ<sup>13</sup>C<sub>2</sub> decreases with an increase in experimental temperature prior to CH<sub>4</sub> substantial cracking. The values of δ<sup>13</sup>C<sub>1</sub> and δ<sup>13</sup>C<sub>2</sub> tend to equalize during CH<sub>4</sub> substantial cracking. The δ<sup>13</sup>C<sub>1</sub>–δ<sup>13</sup>C<sub>2</sub> of mud gas investigated at different depths during shale gas drilling in the Sichuan Basin increases initially, then decreases with further increase in the depth, and finally tends to zero, with only a trace hydrocarbon gas being detectable. Thus, the approximately equal value between δ<sup>13</sup>C<sub>1</sub> and δ<sup>13</sup>C<sub>2</sub> for over-mature shale gas and very low wetness could potentially serve as useful criteria to screen CH<sub>4</sub> substantial cracking. Two geochemical indices to indicate CH<sub>4</sub> substantial cracking in a geological setting are proposed according to the variation production data with the geochemistry of over-mature shale gas in the Sichuan Basin, China.https://www.mdpi.com/1996-1073/15/17/6285over-mature shale gasmagnitude of isotope reversalCH<sub>4</sub> polymerizationCH<sub>4</sub> crackingmud gas |
| spellingShingle | Jingkui Mi Wei Wu Di Zhu Ziqi Feng Effect of Methane Cracking on Carbon Isotope Reversal and the Production of Over-Mature Shale Gas Energies over-mature shale gas magnitude of isotope reversal CH<sub>4</sub> polymerization CH<sub>4</sub> cracking mud gas |
| title | Effect of Methane Cracking on Carbon Isotope Reversal and the Production of Over-Mature Shale Gas |
| title_full | Effect of Methane Cracking on Carbon Isotope Reversal and the Production of Over-Mature Shale Gas |
| title_fullStr | Effect of Methane Cracking on Carbon Isotope Reversal and the Production of Over-Mature Shale Gas |
| title_full_unstemmed | Effect of Methane Cracking on Carbon Isotope Reversal and the Production of Over-Mature Shale Gas |
| title_short | Effect of Methane Cracking on Carbon Isotope Reversal and the Production of Over-Mature Shale Gas |
| title_sort | effect of methane cracking on carbon isotope reversal and the production of over mature shale gas |
| topic | over-mature shale gas magnitude of isotope reversal CH<sub>4</sub> polymerization CH<sub>4</sub> cracking mud gas |
| url | https://www.mdpi.com/1996-1073/15/17/6285 |
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