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AAPG Bulletin, Preliminary version published online Ahead of Print 9 October 2023.

Copyright © 2023. The American Association of Petroleum Geologists. All rights reserved.


Geochemical characteristics, genetic types and sources of gas accumulations in the northern Jizhong subbasin, Bohai Bay Basin, eastern China

Nian Liu12 , Nansheng Qiu2 , Mingkuan Qin1 , Zhenming Li2 , Chuan Cai2 , Yuanjie Wang3 , Qiang Guo1 , and Man Lu4

1 Beijing Research Institute of Uranium Geology, 100029, Beijing, China
2 State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing 102249, China
3 PetroChina Huabei Oilfield Company, Renqiu, Hebei 062552, China
4 Molecular Eco-Geochemistry (MEG) Laboratory, Department of Geological Sciences, University of Alabama, Tuscaloosa, Alabama 35485, USA

Ahead of Print Abstract

Gas source and genetic type identification are important for gas system analysis and successful exploration. However, such crucial information is generally lacking or highly controversial in the northern Jizhong subbasin, Bohai Bay Basin, hindering further gas exploration. In this study, multiple genetic types of gases are identified in the northern Jizhong subbasin, including biogenic gas, coal-derived gas and oil-associated gas. In particular, gases in the shallow Paleogene reservoirs are composed mainly of oil-associated gases derived from sapropelic organic matter in the Paleogene third member of the Shahejie Formation (Es3) and dark shales in the fourth member of the Shahejie and Kongdian Formations (Es4+Ek). Gases in the deeply buried Ordovician and Carboniferous–Permian reservoirs are mainly derived from coal with some contribution from oil-associated gases. The deep gases are mainly derived from the Carboniferous–Permian coal-bearing humic source rocks with contribution from mixed organic matter in the Es4+Ek source rocks. Biogenic gases, mainly present in the Paleogene Es3 reservoirs, are dominated by secondary microbially generated gas via carbon dioxide reduction. Microbially generated gases are probably derived from sapropelic organic matter in the Es3 source rock. Based on the findings, it is concluded that shallow Paleogene rocks might be favorable reservoir zone for primary (kerogen) cracking gases generated from type II1 kerogen. Dry gases derived from type III kerogen and secondary cracking gases from type II1 kerogen in the deep and ultradeep Ordovician and Precambrian–Cambrian reservoirs can be other potential exploration targets in the northern Jizhong subbasin.

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Please cite this AAPG Bulletin Ahead of Print article as:

Nian Liu , Nansheng Qiu , Mingkuan Qin , Zhenming Li , Chuan Cai , Yuanjie Wang , Qiang Guo , Man Lu: Geochemical characteristics, genetic types and sources of gas accumulations in the northern Jizhong subbasin, Bohai Bay Basin, eastern China, (in press; preliminary version published online Ahead of Print 09 October 2023: AAPG Bulletin, DOI:10.1306/10052322134.