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ORIGINAL RESEARCH article
Front. Earth Sci.
Sec. Geochemistry
Volume 13 - 2025 | doi: 10.3389/feart.2025.1577658
This article is part of the Research Topic Shale Oil Micro-Migration and Its Effect on Shale Oil Differential Enrichment View all 7 articles
Light hydrocarbons composition and carbon isotopes unravel the origin of natural gas in Triassic marine strata of Moxi gas field, central Sichuan Basin
Provisionally accepted
Chuyuan Guo 1*
Hu Guoyi 2*
Jin Li 2 Xingwang Tian 3
Lianjie Tian 2
Jinhao Guo 2 Huiying Cui 2 Zhen Liu 1 Xianqing Li 1*- 1 China University of Mining and Technology, Beijing, Beijing, China
- 2 Research Institute of Petroleum Exploration and Development (RIPED), Beijing, Beijing Municipality, China
- 3 PetroChina Southwest Oil and Gasfield Company, Chengdu, Sichuan Province, China
To study the genetic types and origin of natural gas, the light hydrocarbons (LHs) composition, carbon isotopes, chemical compositions, and stable carbon and hydrogen isotopic compositions were analyzed in the Triassic strata of Moxi gas field in the Sichuan Basin. The natural gases from the second member of the Jialingjiang Formation (T2j2) and the first member of the Leikoupo Formation (T2l1) have dryness coefficients higher than 0.997 and contain low content non−alkane gases such as CO2 and N2. The δ13C1 values of natural gas in the Moxi (MX) gas field range from −35.3‰ to −32.9‰, the δ13C2 values range from −34.0‰ to −30.3‰, and the δD1 values range from −144‰ to −120‰. As for light hydrocarbons composition, the C7 LHs are dominated by the methylcyclohexane (MCH), and the C6−C7 LHs have low normal alkane contents. The individual carbon isotopes of light hydrocarbons have the characteristics of δ13C>−28‰. The origin identification indicates that the natural gas in this area is oil−type gas that results from the secondary cracking of crude oil. Our results show that the natural gas in T2j2 of the MX gas field is sourced from the shale gas of the Є₁q, the T2l1 gas is a mixed−source gas from different thermal evolution stages of the Є₁q source rocks, shale gas and oil−cracking gas. The mixing effect is the main reason for the reversed phenomenon (δ13C1 > δ13C2).
Keywords: Moxi gas field, Light hydrocarbons, shale gas, Genetic types, Gas source rock
Received: 16 Feb 2025; Accepted: 14 Mar 2025.
Copyright: © 2025 Guo, Guoyi, Li, Tian, Tian, Guo, Cui, Liu and Li. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence:
Chuyuan Guo, China University of Mining and Technology, Beijing, Beijing, China
Hu Guoyi, Research Institute of Petroleum Exploration and Development (RIPED), Beijing, 100083, Beijing Municipality, China
Xianqing Li, China University of Mining and Technology, Beijing, Beijing, China
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