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AAPG Bulletin, Preliminary version published online Ahead of Print 1 November 2025.

Copyright © 2025. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/10212523056

Origin and source of natural gas in the Upper Paleozoic in the Southwest of the Ordos Basin, China

Kaixuan Liu123 , Jianfa Chen12 , Rao Fu12 , Cong Chen12 , Zeya Chen4 , Shizhen Tao4 , Xinshe Liu3 , and Tuan Gu5

1 State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China
2 College of Geosciences, China University of Petroleum, Beijing 102249, China
3 PetroChina Changqing Oilfield Company, Xi’an, Shaanxi 710018, China
4 Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China
5 PetroChina Liaohe Oilfield Company, Panjin, Liaoning 124010, China

Ahead of Print Abstract

The discovery of the Qingyang gas field in the southwestern Ordos Basin, following over 50 years of petroleum exploration, has generated significant scientific interest in its origins, gas-generation mechanisms, and sources. This paper delves into gas genetic type, thermal maturity, source and the influence of secondary alteration by analyzing the geochemical characteristics of the gas and comparing it with tight sandstone gas found in other parts of the Ordos Basin. The study reveals that the natural gas in the Qingyang gas field is dry. When compared to the Sulige and Dongsheng gas fields, the δ13C and δD of methane are relatively heavier, while the δ13CC2+ (ethane, propane, etc.) are lighter. This suggests that the thermal maturity of the gas in this region is relatively high. The high thermal maturity is attributed to the over-mature thermal cracking of a Permian coal measure source rock. Additionally, the gas contains components from the primary cracking of an Ordovician source rock and the secondary cracking of oil from a Cambrian source rock. This mixing of different gas sources contributes to the unique geochemical characteristics of the gas in the southwestern Ordos Basin. Specifically, the lighter carbon isotope value of heavy hydrocarbons in the gas can be explained by the mixing of sapropelic kerogen-cracking gas and oil-cracking gas, which are rich in 12C. This study further substantiates the validity of multiple marine hydrocarbon source rocks in the Lower Paleozoic of the Ordos Basin, offering significant insights and guidance for future natural gas exploration endeavors.

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Please cite this AAPG Bulletin Ahead of Print article as:

Kaixuan Liu , Jianfa Chen , Rao Fu , Cong Chen , Zeya Chen , Shizhen Tao , Xinshe Liu , Tuan Gu: Origin and source of natural gas in the Upper Paleozoic in the Southwest of the Ordos Basin, China, (in press; preliminary version published online Ahead of Print 01 November 2025: AAPG Bulletin, DOI:10.1306/10212523056.

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