沉积和成岩作用交互约束页岩油生储品质机理分析--以东营凹陷牛庄洼陷古近系沙河街组页岩为例

Mechanism of interaction influence between sedimentation and diagenesis on quality of shale oil generation and storage:A case study of Paleogene shale of Shahejie Formation in Niuzhuang Subsag of Dongying Sag

东营凹陷牛庄洼陷沙三段下亚段和沙四段上亚段页岩油富集高产,属于典型的陆相页岩油,目前对页岩纹层间成岩驱动的物质交换和储集特征认识尚不明确。利用岩石学、微量元素、稀土元素地球化学分析等手段,依据亮晶方解石脉切割穿行、物质转移现象以及页岩生烃和含油性参数,开展沉积和成岩作用交互约束页岩油生储品质机理分析,阐述页岩纹层间物质转移、亮晶方解石脉生成及页岩油运移方式。微区稀土元素地球化学分析结果表明,不同物质纹层内Th和U元素含量由高到低依次为:泥质纹层、亮晶方解石脉、重结晶方解石纹层、泥质纹层与亮晶方解石脉接触面。泥质纹层和亮晶方解石脉的轻、重稀土元素分异明显,表现为显著的轻稀土元素富集、重稀土元素亏损的特征,呈明显Dy元素负异常。重结晶方解石纹层的轻、重稀土元素分异不明显,呈Dy元素负异常。亮晶方解石脉中Th、U和稀土元素含量低于泥质纹层,高于重结晶方解石纹层,是区别亮晶方解石脉和重结晶方解石纹层的重要地球化学指标。压实作用和物质组分含量是影响页岩孔隙度的主要因素。核磁共振实验法测定埋深为3300~3600 m的页岩中孔径大于等于30 nm的孔隙明显减少,孔隙度降幅约为1%/hm。受控于生烃增压导致的超压流体保孔作用的影响,陆源矿物总含量与孔隙度呈正相关关系。水成碳酸盐矿物承受上覆压力能力强,有利于人工压裂,其晶间孔和溶蚀孔孔径大且储油能力好。

The shale oil in the Lower Es3 and Upper Es4 Submembers of Niuzhuang Subsag of Dongying Sag is rich,with high yield,belonging to the typical terrestrial shale oil.Currently,the understanding of material exchanges and reservoir characteristics driven by diagenesis between shale laminae is not clear.The mechanism of the interaction influence of sedimentation and diagenesis on the quality of shale oil generation and storage was analyzed by the petrology,geochemical analysis of trace elements and rare earth elements,and other methods based on the sparry calcite veins and material transfer phenomena,as well as shale hydrocarbon generation and oil-bearing parameters.In addition,material transfer between shale laminae,generation of sparry calcite veins,and shale oil migration were scientifically explained.The geochemical microanalysis of rare earth elements reveals that the Th and U element contents within different material laminae in descending order are as follows:argillaceous layer,sparry calcite vein,recrystallized calcite layer,and contact surface between argillaceous layer and sparry calcite vein.The differentiation of light and heavy rare earth elements in the argillaceous layer and sparry calcite vein is obvious,showing significant enrichment of light rare earth elements and loss of heavy rare earth elements,exhibiting obvious negative anomalies of Dy.The differentiation of light and heavy rare earth elements in the recrystallized calcite layer is not obvious,showing a negative anomaly of Dy.The contents of Th,U,and rare earth elements in the sparry calcite veins are lower than those in the argillaceous layer and higher than those in the recrystallized calcite layer,and it is an essential geochemical indicator to distinguish between the sparry calcite veins and the recrystallized calcite layer.The compaction effect and material component content are the main factors affecting shale porosity.According to the nuclear magnetic resonance experiment,the reduction in pore size greater than 30 nm is the most significant in shale with a burial depth of 3300-3600 m,and the reduction amplitude is about 1%/hm.The total content of terrestrial minerals is positively correlated with porosity due to the effect of overpressure fluid pore retention caused by hydrocarbon pressurization.Hydrogenated carbonate minerals have strong resistance to overlying rock pressure,which is beneficial for artificial fracturing.Their intergranular and dissolution pores have large sizes with superior oil storage capacity.