鄂尔多斯盆地中东部奥陶系风化壳储层稀土元素配分特征及其油气地质意义

REE Pattern Features and Its Petroleum Geology Significance of Ordovician Majiagou Weathering Crust Reservoir in Central and Eastern Parts of Ordos Basin

对鄂尔多斯盆地中东部奧陶系马家沟组风化壳岩溶储层的碳酸盐岩、硫酸盐岩和碎屑岩类岩石样品以及上覆层本溪组碎屑岩样品所作的稀土元素含量与配分特征分析表明,稀土元素分馏特征与富集特征明显,非可溶岩的稀土元素总含量与富集程度高于可溶岩。轻、重稀土元素关系分析表明,可溶岩的轻稀土元素迁移大于重稀土元素的分馏效应,揭示了可溶岩经历了不同的岩溶环境,马家沟组碎屑岩中的稀土元素与上覆层本溪组底部砂泥岩中的稀土元素是同源的。δEu与δCe分析表明,δEu的活化迁移,反映了表生期岩溶环境的存在,而δCe的相对富集,揭示了埋藏期岩溶的发育及其与天然气生成运聚的密切关系。

The total content,chemical attributes and pattern features of REE are analyzed for the soluble carbonate rock and sulfate rock and the insoluble clastic rock samples from the Ordovician Majiagou weathering crust reservoirs as well as the correlating clastic rock samples from the overlying Carboniferous Benxi Fm.in the middle and east parts of Ordos basin.It is shown that the REE is characteristic of obvious fractionation and enrichment and the total REE content and REE enrichment are higher in insoluble rock than in soluble rock.The correlationship between LREE and HREE and the rich or rareδEu andδCe in these rock reveal that they formed either in epidiagenetic or buried karst environments.It is proved that the REE in the Majiagou filling clastic rock was the same source as that in Benxi clastic rock.Development of the paleokarst during buried diagenesis was accompanies with the generation and migration of natural gas.