Mechanism study of organic matter enrichment in fine-grained sediments in continental depression lacustrine basin: an example from the Qingshankou Formation in Changling sag, Songliao Basin
MENG Qingtao1,2, ZHANG Xun1, YANG liang3, GAO Jiajun1, LIU Zhaojun1,2, HU Fei1,2, XING Jilin3, ZHANG Chengming1, KANG Jianan1, CUI Bo1, DONG Qinwei1, ZHANG Enwei1
1 College of Earth Sciences,Jilin University,Changchun 130061,China; 2 Key Laboratory of Oil Shale and Coexistent Energy Minerals of Jilin Province,Changchun 130061,China; 3 Exploration and Development Research Institute,Jilin Oilfield Company,Jilin Songyuan 138000,China; 4 Exploration and Development Research Institute of Northeast Oil & Gas Branch of Sinopec,Changchun 130062,China
Abstract As a large continental depression oil-and gas-bearing basin formed during the Cretaceous period,Songliao Basin contains a huge thickness of lacustrine fine-grained sediments,characterized by great exploration potential for unconventional oil and gas in recent years. The Qingshankou Formation is the key breakthrough layer of shale oil in Songliao Basin,and the mechanism of organic matter enrichment in fine-grained sediments is crucial for unconventional oil and gas exploration. Three wells located in different sedimentary areas in Changling sag of southern Songliao Basin were selected for detailed studies in this study. Based on core observation,organic geochemistry and biomarkers analysis of the fine-grained sedimentary rocks of the Member 1 of Qingshankou Formation(K2qn1),the transgressive systems tract,and the source and preservation conditions of organic matter in different sedimentary environments and processes were analyzed. Then the key control factors of organic matter enrichment were discussed,and the relevant enrichment models were established. Our results show that the organic matter abundance of fine-grained sedimentary rocks of K2qn1 was relatively high,and the kerogen is dominated by type Ⅱ. The overall organic matter abundance was low values in the south but high values in the north,low values in the lower part and high values in the upper part. Normal alkanes in saturated hydrocarbons predominantly exhibit single-peak and pre-peak patterns,with a slight odd-carbon preference. The terpenoids are primarily composed of tricyclic terpenoids and pentacyclic triterpenes. C27-29 regular steroids are dominated by C27 regular steroids. The major compound of the trifluorene series in aromatic hydrocarbons is dibenzothiophene. The organic matter in fine-grained sedimentary rocks of K2qn1 is mostly derived from the endogenous bacteria and algae in lakes,containing a certain amount of terrestrial higher plants. The water body is a weakly reduced,brackish environment. The source of organic matter and salinity are key factors controlling the enrichment of organic matter. Horizontally,the semi-deep lake to deep lake is less affected by riverine influences compared to the delta’s outer front,exhibiting weaker terrestrial input,higher water salinity,superior organic matter types,and greater organic matter richness. Vertically,as the water depth increases,riverine influence diminishes,the water salinity trends upward,the quality of organic matter improves,and organic matter becomes more enriched.
Fund:Co-funded by the Natural Science Foundation of Jilin Province(No. 20230101081JC),the CNPC Funded Project(No.JS2021-W-13-JZ-8-16)and the Program for Jilin University Science and Technology Innovative Research Team(No.2021TD-05)
About author: MENG Qingtao,born in 1984,is a professor at Jilin University.Her studies focus on the evaluation of petroleum geology,geochemistry and evaluation and mineralization of unconventional oil and gas resources.E-mail: mengqt@jlu.edu.cn.
Cite this article:
MENG Qingtao,ZHANG Xun,YANG liang et al. Mechanism study of organic matter enrichment in fine-grained sediments in continental depression lacustrine basin: an example from the Qingshankou Formation in Changling sag, Songliao Basin[J]. JOPC, 2024, 26(2): 401-415.
MENG Qingtao,ZHANG Xun,YANG liang et al. Mechanism study of organic matter enrichment in fine-grained sediments in continental depression lacustrine basin: an example from the Qingshankou Formation in Changling sag, Songliao Basin[J]. JOPC, 2024, 26(2): 401-415.
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