鄂尔多斯盆地富县地区延长组长8油藏油源对比研究

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

关键词:  原油地球化学  油源对比  延长组  富县地区  鄂尔多斯盆地

Key words:  geochemistry of crude oil  oil-source rock correlation  Yanchang Formation  Fuxian region  Ordos Basin

摘要:

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/C₂₉Ts<2,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/C₂₉Ts>2,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。

Abstract:

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.