鄂尔多斯盆地南缘延长组烃源岩地球化学特征及油源对比

Geochemical characteristics of source rocks and oil-source correlation of Yanchang Formation in southern Ordos Basin,China

对鄂尔多斯盆地南缘延长组长6—长9段烃源岩、油砂岩心样品进行了系统的采集,利用热解分析、TOC含量测定、有机碳同位素分析、GC/MS/MS测试等分析手段,对烃源岩生烃特征、沉积环境及油砂的油源特征进行了研究。结果表明:长6—长9段烃源岩均已达到成熟阶段,其中长7_3层为最好烃源岩层,其TOC含量平均为13.99%,干酪根类型主要为Ⅰ型;长6_2层次之,TOC含量平均为4.12%,干酪根类型主要为Ⅰ+Ⅱ_1型;长9段烃源岩TOC含量平均为2.85%,有机质类型主要为Ⅱ_1+Ⅱ_2型。长6—长9段烃源岩样品形成于典型的淡水湖泊环境,长8—长9段沉积时期Pr/Ph>1,沉积水体较浅,为亚氧化强氧化沉积环境,以陆源有机质输入为主;长6—长7段沉积时期Pr/Ph<1为还原环境,沉积水体较深,有机质来源为低等水生生物和陆源高等植物混源。研究区长6—长9段烃源岩生烃特征与其沉积环境息息相关,沉积环境还原性越强,陆源有机质输入越少,烃源岩生烃特征越好。聚类分析油源对比结果显示:研究区长7—长8段油砂样品的油源主要为长7_3层烃源岩。

Core samples of source rocks and oil sands from Yanchang Formation in southern Ordos Basin were collected systematically and the hydrocarbon generation characteristics,sedimentary environment and oil-source correlation of which were studied utilizing various analytical methods.The results show that source rocks in Chang 6 to Chang 9 members are at mature stage of evolution.Among the studied samples,source rocks in Chang 73 member have the best quality with average TOC of 13.99% and mainly kerogen type of typeⅠ.Source rocks in Chang 62 member have the second-best quality with average TOC of 4.12% and kerogen type of typeⅠ＋Ⅱ1.Source rocks in Chang 9 member have average TOC of 2.85% and kerogen type of type Ⅱ1＋Ⅱ2.The source rocks of Chang 6 to Chang 9 members are all formed in the typical fresh lacustrine environment.The source rocks in Chang 8 to Chang 9 members deposited in weak oxidizing to oxidizing environment with swallow water and the organic matter of which was mainly derived from higher plants.The source rock in Chang 6 to Chang 7 members deposited in reducing environment with relatively deep water and the organic matter of which was derived from a source mixed by hydrobios and higher plants.The quality of source rocks in the studied area is closely related to its sedimentary environment.The source rock deposited in reducing sedimentary environment with more hydrobios input in its organic matter source has the best quality.Oil sands in Chang 7 to Chang 8 members are sourced from source rocks in Chang 73 member according to the hierarchical cluster analysis.