泥岩与页岩地化特征对比——以鄂尔多斯盆地安塞地区延长组7段为例

Geochemical comparison of mudstone and shale—A case study of the 7 member of Yanchang Formation in Ansai area, Ordos Basin

范柏江 梅启亮 王小军 孟越 黄启江

Bojiang Fan Qiliang Mei Xiaojun Wang Yue Meng Qijiang Huang

鄂尔多斯盆地安塞地区，延长组7段（长7段）发育优质的页岩与泥岩烃源岩。开展泥岩与页岩的区别研究，有助于评价页岩与泥岩的品质，识别它们对油气资源的贡献。基于25口重点探井开展了岩心描述工作，同时选取泥岩及页岩样品共计81块开展地球化学测试与分析，以获得泥岩与页岩的地化特征并开展差异性对比。结果表明，长7段泥岩与页岩均处于热成熟生油的热演化范围、有机质丰度均达到好烃源岩标准、页岩有机质类型以Ⅰ型与Ⅱ型为主，而泥岩有机质类型以Ⅱ与Ⅱ型为主。在页岩与泥岩的地化特征对比上发现，页岩有机质丰度显著高于泥岩，其中最主要的影响因素是有机碳含量大于4%的页岩样品数量较多；页岩有机质类型更偏于生油，其中最主要的影响因素是高氢指数的腐泥质组分相对丰富；页岩的游离烃、热解烃以及生烃潜量均优于泥岩，但页岩中孔隙及微裂缝对游离烃的统计影响更大；由于页岩孔隙及微裂缝更容易发育，泥岩对烃类的滞留能力可能更强，而页岩中烃类的排运相对容易；泥岩与页岩的生标参数并无显著差异。

High-quality shale and mudstone source rocks are developed in the 7 member of Yanchang Formation (Chang 7 member) in Ansai area within the Ordos Basin.A study of geochemical differences of the two rocks was considered necessary for evaluating their quality and identifying their contributions to oil and gas reservoirs.A core description of the Chang 7 member was then carried out based on 25 key exploration wells and a geochemical comparison of the rocks was also performed based on 81 mudstone and shale samples gathered from the member in the wells.The results show that both shale and mudstone samples are good source rocks with their thermal maturation and organic matter abundance values within favorable ranges, except that the shale samples are dominated by Types Ⅰ and Ⅱ organic matters whereas the mudstone samples are dominated by Types Ⅱ and Ⅱ organic matters.Compared with mudstone in terms of geochemical features, shale has significantly higher abundance of organic matter with more shale samples having values greater than 4% and is more oil-prone as it contains higher content of sapropel.Shale also has higher contents of free and pyrolysis hydrocarbons and greater hydrocarbon-generating potential than mudstone.However, it should be noted that the occurrence of more pores and micro-fractures in shale may have a greater impact on the content measurements of free hydrocarbon.Compared with shale, in which pores and micro-fractures are easily developed and serve as pathways for hydrocarbon expulsion and migration, mudstone demonstrates stronger retention capacity for hydrocarbons.In addition, there is no significant difference between shale and mudstone in terms of biomarker parameters.

10.11743/ogg20200601