鄂尔多斯盆地富县地区延长组长6、长7段原油地球化学特征及油源对比

Geochemical characteristics and oil-source correlation of crude oils in 6th and 7th members of Yanchang Formation,Fuxian area,Ordos Basin

运用原油物性、族组成、生物标志化合物、油—源对比等分析指标,对鄂尔多斯盆地富县地区长6、长7段原油地球化学特征和油源成因进行了分析。富县地区长6、长7段原油物理性质相似,均为低密度、低黏度的轻质原油;原油饱和烃平均质量分数为71.46%,芳烃平均质量分数为13.27%,非烃及沥青质含量相对较低;原油"饱芳比"值较高,平均值为5.43;正构烷烃呈单峰分布,低碳数占优,主峰碳为nC15;生物标志化合物中C30藿烷优势明显;规则甾烷构型均呈反"L"字形分布特征,以C29为主;原油成熟度相近,均为成熟原油;生油母质以低等水生生物为主,含部分陆生高等植物,沉积于弱还原的淡水—微咸水陆相沉积环境;油源对比分析表明,长6、长7段原油与本区长73亚段烃源岩亲缘关系较好,而与长7段上部暗色泥岩及湖盆中心志丹长73亚段烃源岩对比性较差,亲缘关系不明显,因此,认为原油主要来自于本区长73亚段烃源岩。

The geochemical characteristics and oil-source correlation of crude oils in the sixth(Chang 6)and seventh(Chang 7)members of Yanchang Formation in the Fuxian area of the Ordos Basin were studied based on physical properties,group composition,biomarker compounds and oil-source correlation.The Chang 6 and Chang 7 crude oils in the study area are similar in physical properties,both of which are light with a good fluidity.The average mass fraction of saturated hydrocarbons is 71.46%,the average mass fraction of aromatics is 13.27%,and the contents of non-hydrocarbons and asphaltenes are relatively low.The saturated to aromatics ratios of the crude oils are high,averaging 5.43.The n-alkane distribution is dominated by a single peak at C15 and low carbon numbers.The C30 hopane is prominent in biomarker compounds.The regular sterane distribution is anti-"L"type,that is,dominated by C29.Both of the Chang 6 and Chang 7 crude oils are mature.The sedimentary parent material type is lower hydrobiont and contains some terrestrial higher plants,which are deposited in a weakly reduced freshwater-brine water terrestrial sedimentary environment.The oil-source correlation shows that the Chang 6 and Chang 7 crude oils are closely related to the Chang 73 source rocks in this area;however,the relationship with the dark mudstones in the upper part of Chang 7 and the Chang 73 source rocks in the Zhidan area in the basin center is poor.Therefore,it is believed that the crude oil is mainly from the Chang 73 source rocks in this area.