Characteristics of Geochemistry and Depositional Environment of Terrestrial Shales in the First Member of Qingshankou Formation of Changling Fault Depression in the Southern Songliao Basin

doi:10.3969/j.issn.1006-6535.2023.06.008

Abstract

Abstract: In response to the problem of unclear understanding of geochemistry and depositional environment characteristics of terrestrial shale in the first member of Qingshankou Formation of Changling fault depression in the southern Songliao Basin, the experiments on organic geochemistry, molecular geochemistry and elemental geochemistry were systematically carried out to clarify the hydrocarbon generation potential of terrestrial shale in the study area, and to explore the controlling effect of depositional environment characteristics on the enrichment of organic matters. The study results show that the terrestrial shale in the first member of Qingshankou Formation is rich in organic matters, with an average TOC of 1.71% and an average chloroform asphalt "A" of 0.52%, which has good hydrocarbon generation potential. The types of kerogen are mainly Ⅰ and Ⅱ₁, and the thermal evolution of organic matter is at a mature stage, with the average pyrolysis parameter T_max of 447 ℃ and average R_o of 1.06%; the C₂₇-C₂₉ regular sterane indicates that the organic matter of the shale is mainly originated from lower-order aquatic organisms, such as algae, and partly imported from higher-order plants, the ratio of trace elements and biomarker compound parameters indicate that the paleoproductivity level is high, and the shale is originated from saline-water and brackish-water reducing environment, which is favorable for organic matter preservation; the chloroform asphalt "A" has a positive correlation with P/Ti and Sr/Ba, which suggests that the paleoproductivity and the preservation conditions jointly control the organic matter enrichment of shale. According to the evaluation criteria of shale oil "sweet spot" of TOC>2.00% and S₁>1 mg/g, the favorable area is determined to be 5 000 km², and the geological reserves calculated by volumetric method is 54.7×10⁸t. The study is of strategic significance for the evaluation of shale oil resource potential in the southern Songliao Basin.

Key words: geochemistry, depositional environment, terrestrial shale oil, first member of Qingshankou Formation, Changling Fault Depression, Songliao Basin

CLC Number:

TE121.1

Zhao Chenxu, Li Zhongcheng, Guo Shichao, Bao Zhidong, Wei Zhaosheng, Li Lei, Wang Hailong. Characteristics of Geochemistry and Depositional Environment of Terrestrial Shales in the First Member of Qingshankou Formation of Changling Fault Depression in the Southern Songliao Basin[J]. Special Oil & Gas Reservoirs, 2023, 30(6): 55-61.

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