Lithological Differences of Chang 7 Mud-Shale System and Their Controls on Shale Oil Content in Ansai Area, Ordos Basin

doi:10.7657/XJPG20250307

Abstract

Abstract:

Affected by source input and sedimentary cycles, continental mud-shale systems are lithologically complex and diverse. To elucidate the lithological differences of these systems and their controls on shale oil content, the mud-shale system in the 7th member of the Yanchang formation (Chang 7 member) in the Ansai area of Ordos Basin was selected for detailed analysis. By comparing petrological and geochemical characteristics, the development features of mudstone, shale, sandstone, and sand-laminated shale in the study area were identified. Through quantitative evaluation of shale oil content and analysis of geological parameters, the differences in shale oil content between different lithologies and the controlling factors were revealed. The results indicate that shale has the highest content of shale oil, with a poor mobility; sandstone and sand-laminated shale contain moderate content of shale oil, with a good mobility; and mudstone has the lowest content of shale oil, with the poorest mobility. For shale, mudstone, and sand-laminated shale, the higher the total organic carbon content and pyrolysis peak temperature, the higher the shale oil content; the better the organic matter types, the higher the shale oil content. For sandstone, the higher the porosity and permeability, the higher the shale oil content.

Key words: Ansai area, Yanchang formation, lithological difference, shale oil, quantitative evaluation, geological parameter

CLC Number:

P618.12

SHI Liang, ZHANG Yaxiong. Lithological Differences of Chang 7 Mud-Shale System and Their Controls on Shale Oil Content in Ansai Area, Ordos Basin[J]. Xinjiang Petroleum Geology, 2025, 46(3): 308-317.

Figures/Tables 14

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赋存岩性	大量页岩油散失时间/min	散失速度	评价方法	页岩油含量	页岩油可动性
页岩	>45	慢	地球化学法	最高	最差
泥岩	>45	慢	地球化学法	适中	差
砂纹层页岩	30~40	较慢	地球化学法	适中	好
砂岩	<20	快	基于压汞实验的J函数法	最低	最好

有机质类型	岩性	页岩油含量/（mg·g^-1）
有机质类型	岩性	最大值	最小值	平均值
Ⅰ型	页岩	36.8	12.8	21.7
	泥岩	44.7	8.2	26.4
	砂纹层页岩	24.9	7.5	16.1
Ⅱ₁型	页岩	17.7	2.7	11.0
	泥岩	8.4	1.4	4.9
	砂纹层页岩	34.1	10.5	18.1
Ⅱ₂型	页岩	18.5	18.5	18.5
	泥岩	19.6	1.1	9.9
	砂纹层页岩	13.0	7.0	10.0
Ⅲ型	砂纹层页岩	6.2	6.2	6.2