鄂尔多斯盆地富县地区延长组长8油藏油源对比研究

通过对富县地区延长组长6~长9原油及烃源岩的地球化学特征综合对比分析,认为研究区存在长7、长9两套有效烃源岩。长7烃源岩有机质类型为Ⅰ~Ⅱ1型,长9烃源岩的有机类型为Ⅱ1~Ⅱ2型。长7、长9烃源岩中Ts相对含量高于Tm,均达到成熟阶段。长7烃源岩五环三萜烷中C30藿烷丰度相对高于C29藿烷丰度,C30RH/C29Ts2,长7形成于还原环境;长9烃源岩中C30藿烷丰度与C29藿烷丰度基本相似,C30RH/C29Ts2,表明长9为弱氧化-弱还原环境。长6原油饱/芳比值较低,长8原油饱/芳比值较高,说明长6原油和长8原油不同源。长7烃源岩与长9烃源岩在生物标志化合物特征上有明显区别。规则甾烷C27-C28-C29αααR指纹分布样式上,长7呈现"L"型,长9呈现偏"V"型与反"L"型,长8原油呈现偏"V"型分布。研究区长8原油主要来源于长9烃源岩。

Oil-source rock correlation for the Chang-8 oil reservoirs in the Yanchang Formation, Fuxian region, Ordos Basin

Geochemical correlation of the crude oil and source rocks from the Chang-8 to the Chang-9 oil reservoirs in the Yanchang Formation,Fuxian region,Ordos Basin indicates that there occur the Chang-7 and Chang-9 effective source rocks with higher organic matter abundances. The organic matter in the Chang-7 source rocks belongs to the I-II1 types,and that in the Chang-9 source rocks belongs to the II1-II2 types,both of which have higher Ts contents than Tm contents,suggesting a mature stage of the source rocks. In the Chang-7 source rocks,C30 hopane abundances in pentacycloterpane are larger than C29 hopane abundances and the C30RH/C29Ts ratios <2,indicating a reduction environment of the Chang-7 source rocks. In the Chang-9 source rocks,a general similarity in C30 hopane abundances and C29 hopane abundances and C30RH/C29 Ts ratios >2 indicates the weak oxidation-weak reduction environments of the Chang-9 source rocks. The saturated hydrocarbons/aromatic hydrocarbons ratios are lower in the Chang-6 source rocks than those in the Chang-8 source rocks,indicating different sources of the crude oil from the Chang-6 and Chang-8 source rocks. As for the biomarkers,the C27-C28-C29 αααR distribution patterns of regular steranes in the Chang-7 source rocks display the "L" type,those in the Chang-9 source rocks display the "V" or inverse "L" types,and those in the Chang-8 source rocks display the "V" type. The crude oil in the Chang-8 oil reservoirs mainly stemmed from the Chang-9 source rocks in the study area.